Heart

Essential Anatomy and Physiology

The heart is a pumping and hollow muscular organ that is located in the center of the thorax, within the mediastinum and rests in the diaphragm. It is cone-shaped and is tilted forward and to the left. It weighs about 300 grams (g).

Specifically, the heart sits in “the chest within the mediastinum between the two lungs” (Herlihy and Maebius, 2000). Lying toward the left side of the body, about 2/3 of the heart is located to left of the midline of the sternum and 1/3 is located to the right. The upper portion or the base of the heart is located at the second rib. The pointed part of the heart or the apex points to the left and is located at the fifth rib. The heart is supported by a string-like structure called the pericardium which anchors it to the surrounding organs such as the diaphragm and between the lungs.

Contemporary literature and media portray the heart as the seat of emotion and somewhat contributes to the characteristics of a person but the main function of the heart is to pump blood to the body through the blood vessels. This is for the purpose of providing the cells in the body with nutrients and oxygen. The pumping action of the heart is accomplished by its contraction and relaxation or its systole and diastole.

During systole, the heart muscles contract and blood is ejected from the heart and during the diastole, the heart relaxes and its chambers are filled making it poised and ready for another contraction. A normal adult heart beats for about 60-80 times per minute (measured as beats per minute or heart rate). In one minute, the heart approximately pumps 5 liters of blood.

Heart LayersThe heart has three layers namely the endocardium, the myocardium and the epicardium.

The innermost layer is the endocardium. It is consisting of endothelial tissues that line the inside of the heart and the valves (which will be discussed later). These endothelial tissues are continuous with the blood vessels that leave ad enter the heart.

The middle layer or the actual pumping muscle of the heart is the myocardium. It is the thickest of the layers of the heart. It is composed of specialized cells called myocytes. These cells form an interconnected network of muscle fibers that encircle the heart forming a spiral from the base up to the apex in an eight figure pattern (Smeltzer et al., 2008). Since the muscle fibers are arranged in a rather twisted, ring-like fashion this allows the heart to effectively pump blood by pumping and squeezing blood out of its chambers to the body from the atria moving to the ventricles.

The epicardium is the thin outermost layer of the heart that is continuous to the apex of the heart and is encased by the pericardium. The pericardium has two layers, that which adheres with the epicardium otherwise called as the visceral pericardium and that which is attached to the surrounding structures of the heart, the parietal pericardium. The parietal pericardium attaches to the great vessels, diaphragm, sternum, vertebral column and supports the heart in the mediastinum (Smeltzer et al., 2008). Between the

visceral and the parietal pericardium is the pericardial space/cavity. The pericardial membrane secretes slippery serous fluid (and contains about 30 ml) that helps lubricate the space allowing easy sliding when the heart contracts and relaxes, avoiding any rubbing or friction. Any condition that impairs the capability of the membrane to secrete fluid, increase the fluid or produce any constriction,

makes the heart unable to pump enough blood to the entire body. The condition when excessive fluid in the pericardial space diminishes the filling of the heart is called cardiac tamponade.

The heart has two pumps that serve two types of circulation. The right pump or the right ventricle receives blood from the entire body (systemic circulation) and pumps blood to the lungs (pulmonary circulation) for gas exchange. The left pump or the left ventricle receives blood from the lungs (pulmonary circulation) and pumps blood to the entire body (systemic circulation).

Chambers and Large VesselsThe human heart has four chambers or rooms. These rooms are divided into the upper receiving rooms and the lower receiving rooms and between the left side and the right side. The upper chambers are called atria (sing. atrium) and the lower chambers are called ventricles. These atria and ventricles are separated by a large septum. The atria are separated by the interatrial septum and the ventricles by the interventricular septum.

The right atrium receives blood from the systemic circulation via the superior and inferior vena cava which subsequently carries blood from the upper part and lower part

of the body. Once the right atrium is filled it empties blood to the right ventricle. The right ventricle receives blood from the right atrium and pumps and delivers it to the lungs via the right and left pulmonary arteries (hence arteries do not necessarily carry oxygenated blood). The left atrium receives the oxygenated blood from the lungs via the left and right pulmonary veins and empties it to the left ventricle. Once filled, the left ventricle then pumps the blood to the entire body via the largest artery in the body, the aorta.

One may have the idea that because the right ventricle pumps blood into the pulmonary circulation which is relatively smaller than the systemic circulation, the right ventricle may then be smaller in size than the left. This is true. Because the workload of the left is

harder, it has relatively thicker muscles than the right which makes it bigger.

Another important parts of the heart is its valves. Imagine the door in your house. You cannot enter your house if you won’t open it. Exactly! Valves act as doors mainly to act as stoppers of blood so that when the heart contracts no blood

backs up into the previous circulation (regurgitate). The valves keep a unidirectional flow of blood, specifically in a forward direction. In the heart, there are four valves.

The atrioventricular valves (AV valves) are those that are located between the atria and ventricles. They have cusps or flaps. The right AV valve has three cusps and so it is named tricuspid valve while the left AV valve only has two that’s why it is called bicuspid valve (or mitral valve because they are said to resemble a bishop’s mitre). These valves are entrance valves because blood flows from the atria to the ventricles through these valves and they prevent the regurgitation of blood from the ventricles to the atria duration ventricular contraction (pumping). When the ventricles are relaxed, these valves hang loosely allowing blood from the atria to flow through the ventricles. When the ventricles contract the pressure of the blood pushes the valves outward toward the atria where they close. They are not completely pushed away into the atria because these valves are supported by a very strong fibrous band of tissue called the chordate tendinae which holds them just right so that they are closed during contraction.

The semilunar valves are the exit valves because blood is pumped outside the chambers through them hence they are termed exit valves. They are termed semilunar because they resemble a half-moon, in fact the two semilunar valves are each composed of three half-moon leaflets. The two semilunar valves are the pulmonic valve/pulmonary valve/right semilunar valve and the aortic valve/leftsemilunar valve.

The pulmonic valve is located between the right ventricle and the pulmonary artery. When the right ventricle contracts, blood is forced to the pulmonary circulation and this opens the valve. When the right ventricle relaxes, the pressure of the pulmonary circulation exceeds that of the right ventricle and it closes the valve the same way as that of the atrioventricular valves.

The aortic valve is located between the left ventricle and the aorta. When the left ventricle contracts the aortic valve is opened and blood is pumped into the aorta. When the ventricle relaxes the pressure of the systemic circulation exceeds that of the ventricle, closing the valve and preventing back flow of blood.

Blood Flow through the Human Heart

Right Atrium

Tricuspid Valve

Right Ventricle

Pulmonic Semilunar Valve

Pulmonary Artery (Main)

Left and RightPulmonary Arteries

Pulmonary Capillaries (Lungs)

Pulmonary Veins

Left Atrium

Bicuspid Valve

Left Ventricle

Aortic Valve

Aorta

Heart Sounds

The vibrations of the closing of the heart valves produce the heart sounds (lubb-dupp) that healthcare professionals listen in order to detect any heart abnormalities. Lubb, the first heart sound is due to the AV valve closure at the beginning of the ventricular contraction while the dupp, the second heart sound, is due to the semilunar valves’ closure during the ventricular relaxation. Murmurs are abnormal heart sounds (Herlihy and Maebius, 2000). The location of the heart sounds are shown in the table below (Murmurs recognition –part 1, 2009):

Aortic area Second intercostals space to the right of the sternumPulmonic area Second intercostals space to the left of the sternumErb’s point Third intercostals space to the left of the sternum (S2 is

best heard)Right ventricular/tricuspid area

Fourth and/or fifth intercostal spaces to the left of the sternum

APEX/Mitral area Fifth intercostals space to the left of the sternum and mid clavicular

S1 is produced the AV valves’closure

S2 is produced by the semilunar valves’closure

Gallops according to Back and Hawks (2005) are diastolic filling sounds that “occur during the two phases of ventricular filling. Sudden changes of inflow volume cause vibrations of the valves and ventricular supporting structures, producing low-pitched sounds that occur either early (S1) or late (S4) in diastole”. These sounds are said to mimic the sounds of a gallop, thus the name.

S3, a dull and low-pitched sound and is “caused by the oscillation of blood back and forth between the walls of the ventricles initiated by inrushing blood from the atria” ((Murmurs recognition –part 1, 2009). “An S3 gallop is considered a normal finding in children and young adults. In adults older than 30 years of age, an S3 is considered characteristic of left ventricular dysfunction” (Back and Hawks, 2005).

S4, the fourth heart sound, a rare heart sound said to occur immediately after S1, is also called atrial gallop. It is a soft, low-pitched sound that is mostly heard on conditions involving ventricular stiffness like hypertrophy, fibrosis, and ischemia (Back and Hawks, 2005). Persons with long standing hypertension may also have this extra heart sound ((Murmurs recognition –part 1, 2009)

Coronary Arteries and Blood Supply to the MyocardiumThe coronary arteries carry the blood that nourishes the heart. Its name comes from the Latin word corona which means a crown because these arteries resemble a crown (Herlihy and Maebius, 2000). These arteries originate from the aorta just above the aortic valve (Smeltzer et al., 2008). The left side of the heart is supplied by the left coronary artery.

This artery continues into left main coronary artery which branches into the left anterior descending artery that supplies the anterior portion, and the circumflex artery which circles around the lateral left into the posterior portion of the left heart. The right side of the heart is supplied by the right coronary artery while the posterior part is supplied by the posterior descending artery (which is a branch of the right coronary artery).

The large metabolic requirement of the heart is such that it extracts approximately 70-80% of the

oxygen delivered while other organs only require an average of 25%. It is also important to note that unlike other arteries that receive blood during the systole or the ventricular contraction, the coronary arteries receive blood during the diastole or the ventricular relaxation. This is because contraction tightens the arteries disabling blood from entering it.

Cardiac Conduction System

The cardiac conduction system generates and transmits electrical impulses throughout the myocardium stimulating it to contract starting from the atria to the ventricles. The coordination between the atria and ventricles’ contraction allows perfect timing for the ventricles to empty first before receiving blood from the atria. Thanks to the characteristics of these specialized cells for providing this perfect synchrony, to wit:

Automaticity- the ability to initiate electrical impulses in themselves (unlike the skeletal muscles which need the prompting of the motor neuron in order to move, the cardiac muscles simply beats in itself with the help of this specialized cells)

Excitability- the ability to respond or be stimulated by any electrical impulse

Conductivity- the ability to deliver or carry or transmit electrical impulses from cell to cell

Refractoriness- the heart is unable to respond to any stimulus while still in a state of depolarization from an earlier stimulus.

The conduction system consists of the sinoatrial (SA) node, atrial conducting fibers, atrioventricular (AV) node, and the His-Purkinje system.

In the upper posterior wall of the right atrium just in the junction between the atrium and the superior vena cava is the sinoatrial node. It is the primary pacemaker of the heart. This means that it has overall control of the rate of the firing of electrical impulses. It has an inherent firing speed of 60-100 impulses per minute in a resting state. The atrial conducting fibers allow the conduction of electrical impulses from the SA node to the AV node in the right atrial wall. Then, the AV node, through some delays, relays the impulse to the ventricles. By the way, the delays in the AV node helps the ventricles to have some time to contract and completely empty before receiving yet another electrical signal to contract. Also, it has an average firing speed of 40-60 impulses per minute.

After receiving the impulse, it will then be conducted to the specialized group of cells referred to as the bundle of His which eventually branches off to the right and left bundle branches subsequently delivering impulses to the right and left ventricles. From then on, the impulses travel the terminal point or the end of the conduction system which is the

Purkinje fibers. These fibers making up the His-Purkinje system are fast conducting fibers allowing the immediate conduction of impulses throughout the ventricles (but left in themselves they only have an average firing rate of 30-40 impulses per minute). Then, after these events, the myocardial cells are stimulated to contract.

Below is a diagram showing the pathway of the electrical impulses of the heart

There are some times when the SA node (through some conditions) loses its ability to fire impulses. In these instances, another node must shoulder the responsibility of the role of a pacemaker, and the best candidate for this is the AV node. If this happens, health professionals term those impulses as having an ectopic focus because they originate from another site of the heart other than the normal which is the SA node. Patient who has this condition is in danger of not having enough nutrients and oxygen being delivered throughout the body because the AV node can only fire 40-60 beats as an average. Any further disturbance to the rhythm of the heart (called as dysrythmias) may threaten the patient. An example for this one is ventricular fibrillation wherein the muscles quiver instead of actually contracting. This particular dysrthmia can kill a person.

Electrocardiogram (ECG or EKG)

The ECG is a very important diagnostic tool in evaluating the heart rhythm and therefore heart condition in general. Even small changes in the electrical activity of the heart can be detected by ECG. There exist different types of ECGs: 12-lead, 15 lead, and 18-lead types, the Holter or continuous monitoring, and the Signal-averaged. Analysis of the

Sinoatrial (SA) Node

Atrial conducting Fibers

Atrioventricular (AV) Node

Bundle of His

Bundle Branches (right and left)

Purkinje Fibers

different ECG forms allows the evaluation of the cardiac rate, rhythm and electrical conduction. ECG is very common because it is non-invasive, easily procured, and is not costly.

For the very purpose of basic ECG, the most common type which is the 12-lead ECG will be discussed here.

A while ago, it has been discussed that the heart, through its specialized cells sends forth electrical impulses throughout its parts in order to stimulate its muscles to contract. ECG captures or records that electrical impulse on paper (a specialized ECG strip) by placing electrodes on the surface of

the chest and on the limbs. “These electrodes detect the magnitude ad direction of electrical currents produced in the heart” and “they attach to the electrocardiograph by an insulated wire called a lead” (LeMone and Burke, 2008). The electrical impulses recorded by the ECG machine are shown in the strip as a series of waveforms. The different views of these electrical activities (horizontal and vertical planes) allow a multi-directional approach in looking at it, much like in looking at an object in different angles.

According to Fauci et al. (2009) and LeMone and Burke (2008), the waveforms of the ECG are labelled alphabetically namely:

P wave- stands for the atrial depolarization and contraction. It may be absent if the atrium is not acting as a pacemaker.

PR interval- represents the time required for the electrical impulse to travel to the AV node, measured from the beginning of the p wave to the beginning of the QRS but if Q is not appreciated well, it can be measured up to the R wave.

QRS complex- represents the ventricular depolarization and contraction.

J point- junction between the QRS complex and the ST segment .

ST-T-U complex (ST segment, T wave, U wave)- stands for the ventricular repolarization.

ST segment- signifies the beginning of ventricular repolarization and the beginning of this ST segment (after the end of QRS) to the beginning of T wave should be isoelectric or flat lined.

T wave- represents the ventricular repolarization.

QT interval- is from the beginning of the QRS complex to the end of T wave and it represents the total time of ventricular depolarization and repolarization.

U wave- thought to indicate repolarization of the Purkinje fibers is not normally seen but us commonly seen in hypokalemic conditions.

Atrial repolarization has very low amplitude that it cannot be detected normally by the ECG also because it occurs during the ventricular depolarization.

ECG Basic Illustrations

The standard ECG has 6 limb leads used to view the heart in a frontal and vertical perspective and another 6 precordial leads which is used to look at the heart in the horizontal plane.

The limb leads have 3 unipolar (aVR, aVL, and aVF) leads and 3 bipolar (I, II, III) leads. “The bipolar leads have two electrodes and measure the difference in electrical potential flowing through the heart between two extremities. The unipolar leads compare the electrical poptential of a positive electrode, placed on one limb, and a negative pole within a central terminal that averages the potential of the other two limb leads” (Black and Hawks, 2005).

Bipolar Leads (uses two electrodes of opposite polarity: negative and positive)

Lead I- measures the difference in electrical potential between the left arm and right arm.

Lead II- measures the difference in electrical potential between the left leg and the right arm.

Lead III- measures the difference in potential between the left leg and the left arm.

Augmented (a)Unipolar Leads (uses one positive electrode and a negative reference point at the center of the heart)

aVR- measures the electrical potential between the center of the heart and the right arm.

aVL- measures electrical potential between the center of the heart and the left arm.

aVF- measures electrical potential between the center of the heart and the left leg (Black and Hawks, 2005; LeMone and Burke, 2008).

The precordial leads or the V leads view the heart in a horizontal plane and includes the six unipolar leads which are the V1, V2, V3, V4, V5, and V6. They compare the six different chest locations (from which they are placed) to the center or the “negative terminal that represents an average potential of the three standard limb leads” (Black and Hawks, 2005).

Because the 12-lead ECG permits a multidirectional view of the heart, any minor pathologic changes that alter the electrical conduction can be easily detected. There are different views from different leads oriented at the different surfaces of the myocardium, Black and Hawks (2005) have shown them as follows:

Leads I, aVL, V5, and V6 record electrical events occurring on the lateral surface of the left ventricle.

Leads II, III, and aVF record electrical events occurring on the inferior surface of the left ventricle

Leds V1 and V2 record electrical impulses occurring on the surface of the right ventricle and anterior surface of the left ventricle

Leads V3 and V4 record electrical impulses occurring within the septal region of the left ventricle

In interpreting ECG records, it is important to note that it is an advance skill and therefore it needs further training but there are simple basic ways of interpretations. Below are the steps proposed by LeMone and Burke (2008):

Step 1: Determine the rate. Assess heart rate. Use P waves to determine the atrial rate and R waves for the ventricular rate.

Count the number of complexes in a 6-second rhythm strip by marking the top of the strip at 3-second intervals, and then multiply it by 10. The resulting value is only an estimate of the heart rate but is useful in times when rhythm is irregular.

Count the number of large boxes between two consecutive complexes, and divide 300 (large boxes in 1 min) by this number.

Count the number of small boxes between two consecutive complexes, and divide 1500 (small boxes in 1 min). If there are 25 small boxes between R waves, divide 1500 by 25 and you will have 60. This is a precise measure of heart rate.

Step 2: Determine regularity. It is the consistency with which the P waves r QRS complexes occur. It is determined by measuring the interval between consecutive waves. Use a blank paper and place it on top of the ECG strip. Measure and mark the distance between the first and second complex then do the same with the next or consecutive complexes. Any variation or inconsistencies means there is an irregular pattern. A regularly irregular pattern means that though complexes’ patterns are irregular or not the same, at least there is a consistency in there pattern or it is predictable. If a pattern is irregularly irregular, it is very inconsistent or unpredictable.

Step 3: Assess P wave. P wave absence means that there might be an ectopic focus. As discussed above, an ectopic focus means that other than the normal SA node origin of electrical impulse, another area like the AV node for example has taken the

responsibility of sending or leading the electrical impulse sending throughout the heart. All P waves should also be the same in size and shape.

Step 4: Assess P to QRS relationship. There should be 1 P wave and QRS complex following it.

Step 5: Determine interval durations. Measure the intervals of small boxes between each PR interval, QRS complex, and the QT interval and multiply them each by 0.04 to convert them to seconds. Then note and compare to the standard or normal time if there is a delay or premature impulses.

Step 6: identify abnormalities. A good example would be ST segment elevation, T-wave inversion, abnormal Q wave which is seen in myocardial infarction (Silvestri, 2006). Other changes are present in hypo- and hyperkalemia as shown below:

Hypokalemia VS Hyperkalemia

Important Routine Diagnostic TestsComplete Blood Cell Count

This routine laboratory test is important because red blood cells (RBCs) or erythrocyte count is usually elevated in conditions where in there is a decreased oxygenation (right-left congenital shunts). It is however decreased in rheumatic fever and endocarditis (Black and Hawks, 2005).

Hematocrit measuring is an easy way to ascertain RBC concentration. Elevated hematocrit can result from obstructive lung disease and other conditions such as hypovolemic shock and excessive diuresis.

White blood cell (WBC) count is elevated in infectious state like infective endocarditis and pericarditis and also elevated after myocardial infarction (MI).

Cardiac Enzymes

Enzymes are special proteins present in large amounts in the myocardial tissue. They help catalyze chemical reactions inside the cells. Certain conditions that damage the heart cells as in myocardial infarction releases these enzymes in the blood. These heart enzymes may reflect myocardial integrity or damage.

Myoglobin is released within 1 to 2 hours of infarction. It is an early indicator but is not reliable when taken after several hours after myocardial infarction. Also, it may be present in muscle damage, trauma and kidney failure.

Creatinine kinase (CK) and lactic dehydrogenase (LDH) occur in sequence after MI. However, because it is also present in other organs, its isoenzymes are used instead to be more specific. The process termed as electrophoresis is used to identify these enzymes. There are 3 isoenzymes of CK:

CK-MM (in skeletal muscle) CK-BB (in the brain) CK-MB (myocardial muscle)

MB is elevated immediately within 6 to 8 hours after the onset of MI and it reaches maximum levels after 14 to 36 hours. It normalizes after 48 to 72 hours. Therefore blood during admission should be taken immediately and two samples separated by at least 4 hours should be obtained.

LDH has 5 isoenzymes but LDH1 and LDH2 are cardiac specific. A phenomenon termed as flipped LDH means that LDH1 is higher in concentration than LDH2 signifying myocardial necrosis.

The enzyme troponin is another useful indicator in MI. It has 3 components: I, C, and T. “Troponin I modulates the contractile state, troponin C. Binds calcium, and troponin T binds I and C” and they “are useful for diagnosis after 4 to 6 hours have elapsed. Once present, troponin I persists for 4 to 7 days” ( Black and Hawks, 2005).

Blood Coagulation Tests

There are certain conditions (infective endocarditis, atrial fibrillation, presence of prosthetic valves) that put a person at risk for thrombi formation and so prothrombin time and partial thromboplastin time are indicated.

Other Diagnostic Tests of Cardiac Disorders taken from LeMone and Burke (2008). It is important to note that ECG was not included below as it was already presented above.

Name of Test LipidsPurpose and Description Blood lipids are cholesterol, triglycerides, and phospholipids. They circulate bound to proteins, and so are known as lipoproteins. Lipids are measured to evaluate risk for CAD and to monitor effectiveness of anti-cholesterol medications.

Normal Values:Cholesterol: 140-200 mg/dLTriglycerides: 40-190 mg/dLHDL: Men= 37-70 mg/dL Women= 40-88 mg/dLLDL: less than 130 mg/dL (Note: Normal values may vary by laboratory)Related Nursing care Cholesterol levels alone may be measured at any time of the day, regardless of food or fluid intake. When measuring triglycerides and lipoproteins (HDL and LDL), fasting for 12 hours (except for water) with no alcohol intake for 24 houra prior to the test is recommended.

Name of Test Chest x-rayPurpose and Description An x-ray of the thorax can illustrate the contours, placement, and chambers of the heart. It may be done to identify heart displacement or hyperthropy, or fluid in the pericardial sac.Related Nursing Care No special preparation is needed.Name of Test Stress/Excercise tests

Treadmill testPurpose and Description Stress testing is based on the theory that CAD (coronary artery disease, emphasis added) results in depression of the ST segment with excercise. Depression of the ST segment and depression or inversion of the T wave indicates

myocardial ischemia. When the client is walking on a treadmill machine, the work rate of the heart is changed every 3 minutes for 15 minutes by increasing the speed and degree of incline by 3% each time. Clients exercise until they are fatigued, develop symptoms, or reach their maximum predicted heart rate.Related Nursing Care For all stress/exercise tests: Ask the client to wear comfortable shoes, and to avoid food, fluids, and smoking for 2 to 3 hours before the test, assess for events that contraindicate the tests: recent myocardial infarction; severe, unstable angina; controlled dysrhythmias; congestive heart failure; or recent pulmonary embolism.

Name of Test Thallium/technetium stress test (myocardial imaging perfusion test, cardiac blood pool imaging)Purpose and Description Thallium stress test: Thallium-201, a radioisotope that accumulates in the myocardial cells, is used during the stress test to evaluate myocardial perfusion. Second scans are done 2 to 3 hours later when the heart is at rest; this is to differentiate between an ischemic area and an infracted or scarred area of myocardium.Exercise technetium perfusion test: Technetium 99m-laced compounds are administered and a scan is done to evaluate cardiac perfusion, wall motion, and ejection fraction. This is probably the most useful noninvasive test to diagnose and monitor CAD.Related Nursing Care Assess medications; those that affect the blood pressure or heart rate should be discontinued for 24 to 36 hours prior to the test (unless the test is being done to monitor the effectiveness of the medications.)Name of Test Nuclear persantine [dipyridamole] stress testPurpose and Description This test is used when the client is not physically able to walk on the treadmill. Persantine, given IV, dilates the coronary arteries and increases myocardial blood flow. Coronary arteries that are not narrowed from CAD cannot dilate to increase myocardial perfusion.Related Nursing Care Client is NPO after midnight except for water. Food, fluids, and drugs that contain caffeine should be avoided for 24 hours prior to the test, as should decaffeinated fluids. Some drugs, such as theophylline preparations, are discontinued for 36 hours prior to the test.Name of Test Nuclear dobutamine stress testPurpose and Description Dobutamine is an adrenergic drug that increases coronary oxygen consumption and thus increases coronary blood flow.Related Nursing Care Client is NPO after mignight except for water. Discontinue beta-blockers, calcium channel blockers, and ACE inhibitors for 36 hours prior to the test.Name of Test Magnetic resonance imaging (MRI)Purpose and Description An MRI may be used to identify and locate areas of myocardial infarction.Related Nursing Care Assess for any metallic implants (such as pacemaker, body piercing, or artificial joint), which would contraindicate the test.Name of Test Computed tomography (CT) scanPurpose and Description A CT scan may be conducted to quantify calcium deposits in the coronary arteries.

Related Nursing Care Assess for allergy to iodine or seafood of contrast medium is to be administered.Name of Test Cardiolite scanPurpose and Description Used to evaluate blood flow in different parts of the heart. Cardiolite (technetium 99m sestamibi) is injected to increase blood flow to coronary arteries. These scans may be done in conjunction with a treadmill test.Related Nursing Care See information in this table for treadmill test. Instruct the client to avoid intake of the caffeine for 12 houra before having a test with dipyridamole cardiolite.Name of Test Positron emission tomography (PET)Purpose and Description following intravenous injection of radionuclides, and the resulting images compared for myocardial perfusion and myocardial metabolic function. A stress test (treadmill) may be a part of the test. If the myocardium is ischemic or damaged, the images will be different. Normally, the images will be the same.Related Nursing Care Assess client’s blood glucose: For accurate metabolic activity images, the blood glucose level must be between 60 and 140 mg/dL. If exercise is included in the test, the client will need to be NPO and avoid smoking and caffeine for 24 hours prior to the test.Name of Test Blood pool imagingPurpose and Description Following intravenous injection of technetium 99m pertechnetate, sequential evaluation of the heart can be performed for several hours. Useful for evaluation of cardiac status following myocardial infarction and congestive heart failure and effectiveness of cardiac medications. Can be done at the client’s bedside.Related Nursing Care No special preparation is needed.Name of Test Echocardiogram

M-mode Two-dimensional (2-D) Cardiac Doppler Color Doppler Stress echocardiogram

Purpose and Description Echocardiograms use a transducer to record waves that are bounced off the heart, and to record the direction and flow of blood through the heart in audio and graphic data. An M(motion)-mode echocardiogram records the motion, wall thickness, and chamber size of the heart. A 2-D echocardiogram provides a cross-sectional view of the heart. Color flow imaging combines 2-D echocardiography and Doppler technology to evaluate the speed and direction of blood flow through the heart, which can identify pathology such as leaky valves. Stress echocardiography combines a treadmill test with ultrasound images to evaluate segmental function and wall motion. If the client is not physically able to exercise, IV dobutamine may be administered and ultrasound images takes.Related Nursing Care No special preparation is needed; see related nursing care for the client having a treadmill test for a stress echocardiogram.Name of Test Transesophageal echocardiography (TEE)Purpose and Description Allows visualization of adjacent cardiac and extracardiac structures to identitfy or monitor mitral and aortic valve pathology, left atrium intracardiac thrombus, acute dissection of the aorta, endocarditis, perioperative left

ventricular function, and intracardiac repairs during surgery. A transducer (probe) attached to an endoscope is inserted into the esophagus, and images are taken. Concurrent IV contrast medium, Doppler ultrasound, and color flow imaging may be used.Name of Test Cardiac catheterization (coronary angiography, coronary arteriography)Purpose and Description A cardiac catheterization may be performed to identify CAD or cardiac valvular disease, to determine pulmonary artery or heart chamber pressures, to obtain a myocardial biopsy, to evaluate artificial valves, or to perform angioplasty or stent an area of CAD. The test is performed by inserting a long catheter into a vein or artery (depending on whether the right side or the left side of the heart is being examined) in the arm or leg. Using fluoroscopy, the catheter is then threaded to the heart chambers or coronary arteries or both. Contrast dye is injected and heart structures are visualized and heart activity is filmed. The test is done for diagnosis and before heart surgery.

Right cardiac catheterization: The catheter is inserted into the femoral vein or antecubital vein and then through the inferior vena cava into the right atrium to the pulmonary artery. Pressures are measured at each site and blood samples can be obtained for the right side of the heart. The functions of the tricuspid and pulmonary valves can be observed.

Left cardiac catheterization: The catheter is inserted into the brachial or femoral artery and advanced retrograde through the aorta to the coronary arteries and/or left ventricle. The patency of the coronary arteries and/or functions of the aortic and mitral valves and left ventricle can be observed.

Nursing Care: Cardiac Catheterization

Before the Procedure Explain the procedure to the client. No food or fluids are allowed for 6 to 8 hours before the test. Assess for allergies to seafood, iodine contrast dyes (if previous tests have been

done). If an allergic response to the dye is possible, antihistamines (such as Benadryl) or steroids may be administered the evening before and the morning of the test.

Assess for use of aspirin or NSAIDs (risk of bleeding), Viagra (risk of heart problems), or history of kidney disease (dye used may be toxic to the kidneys).

Discontinue oral anticoagulant medications. Heparin may be ordered to prevent thrombi.

An IV of 5% D5W is started at a keep-vein-open rate (to be available if emergency drugs have to be administered).

Establish baseline of peripheral pulses. Take and record baseline vital signs.

Procedure

Client is positioned on a padded table that tilts. A local anesthetic is used at the site of catheter insertion. ECG leads are applied and vital signs are monitored during the procedure. The client lies supine and is asked to cough and deep breathe frequently. The procedure takes ½ to 3 hours.

Tell the client that a hot, flushing sensation may be felt for a minute or two when the dye is injected.

After the Procedure Monitor vital signs every 15 minutes for the first hour and then every 30 minutes

until stable. Assess cardiac rhythm and rate or alterations. Assess client for complaints of chest heaviness, shortness of breath, and abdominal or groin pain.

Monitor catheter insertion site for bleeding or hematoma. Administer pain medications as prescribed. Instruct client to remain on bed rest for 6 to 12 hours (or as ordered). If a

collagen-like plug was inserted after removal of the catheter, only a 2- to 3-hour bed rest is necessary.

Encourage oral fluids unless contraindicated (i.e., if the client has congestive heart failures).

Name of Test PericardiocentesisPurpose and Description This procedure is performed to remove fluid from the pericardial sac for diagnostic or therapeutic purposes. It may also be done as an emergency procedure for the client with tamponade (which may result to death). A large-gauge (16 to 18) needle is inserted to the left of the xiphoid process into the pericardial sac and excess fluid is withdrawn. The needle is attached to an ECG lead to help determine if the needle is touching the epicardial surface, thus preventing piercing of the myocardium.

Nursing Care: Pericardiocentesis

Before the Procedure Gather all supplies:

a. Pericardiocentesis trayb. ECG machine and electrode patchesc. Emergency cart with defibrillatord. Dressinge. Culture bottles (if indicated)

Reinforce teaching and answer questions about the procedure or associated care. Provide emotional support.

Ensure that informed consent has been obtained. Provide privacy. Obtain and document baseline vital signs. Connect the client to a cardiac monitor; obtain a baseline rhythm strip for

comparison during and after the procedure. Connect the precordial ECG lead of the hub of the aspiration needle using an

alligator clamp.

During the Procedure Follow standard precautions. Position seated at a 45- to 60-degree angle. Place a dry towel under the rib cage

to catch blood or fluid leakage. Observe the ST segment for elevation and the ECG monitor for signs of

myocardial irritability (PVCs) during the procedure. These indicate that the needle is touching the myocardium and should be withdrawn slightly.

Notify the physician of changes in cardiac rhythm, blood pressure, heart rate, level of consciousness, and urine output. These may indicated cardiac complications.

Monitor central venous pressure (CVP) and blood pressure closely. As the effusion is relieved, CVP will decrease, and BP will increase.

After the Procedure Document the procedure and the client’s response to and tolerance of the

procedure. Continue to monitor vital signs and cardiac rhythm every 15 min during the first

hour, every 30 min during the next hour, every hour for the next 24 hours. Record the amount of fluid removed as output on the intake and output record. If indicated, send a sample of aspirated fluid for culture and sensitivity and

laboratory analysis. Assess heart and breath sounds.

Developmental ConsiderationsFetal Circulation

The blood circulation of the fetal developing heart is different from that of an adult. The pulmonary system, particularly the lungs of a fetus is not yet fully developed or is not yet used because the fetus is floating inside the mother’s womb. During this time the fetus relies on the placental nourishment and oxygen supply. So to discuss briefly the fetal

circulation and anatomy is a very important task to understand certain disease conditions (congenital heart disease).

Because the lungs are limited in their capacity to accommodate blood two shunts are helpful during this time. The foramen ovale that connects

(directly) the right and left atria allows blood to bypass the lungs by shunting it before entering the right ventricle.

However, in order to develop the right ventricle should at least receive some blood and this is the case. Indeed, the right ventricle still receives blood but only in small amounts. After passing the tricuspid valve and pafter being pumped by the right ventricle the blood is delivered via pulmonary artery but is shunted to the descending aorta by the ductus arteriosus. Therefore the lungs only recieve minimal blood necessary for its development.

The Fetal Circulation taken from Hope (2010):

1. Oxygen from the placenta travels to the umbilical vein bringing oxygen and nutrients.

2. Some of the blood flows to the hepatic circulation, others bypass the liver and pass through the ductus venosus.

3. The blood from the lower parts of the lower parts of the body together with the blood in the ductus venosus flows toward the inferior vena cava.

4. Some of the blood goes from the right atrium goes to the right ventricle via the tricuspid valve while others pass the foramen ovale leading to the left atrium.

5. From the left atrium, it goes towards the left ventricle, mixing with the poorly oxygenated blood from the lungs and then pumped towards the ascending aorta.

6. From the ascending aorta, the blood is pumped to the upper parts of the body like the heart, neck, head and upper limbs.

7. Then perfuse to the placenta via the two umbilical arteries.

8. Meanwhile the blood that enters the right ventricle together with the poorly oxygenated blood from the head and upper extremities returns to the right side of the heart by the way of the superior vena cave then, passes through the pulmonary artery wherein 10% enters the lungs, most of the blood bypasses the lungs which is then pumped to the ductus arteriosus going to the descending aorta.

9. The blood is the pumped and perfused to other parts of the fetus.

10.The blood then returns to the placenta via the two umbilical arteries.

Sources:

LeMone, P., and Burke, K. (2008). Medical-Surgical Nursing: Critical Thinking in Client Care. 4th Edition. New Jersey: Person Prentice hall. Page 941-949

Silvestri, L. (2006). Comprehensive Review for the NCLEX-RN Examination. 3rd Edition. Singapore: Elsevier. Page 782, 795

Black, J., and Hawks, J. (2005). Medical-Surgical Nursing: Clinical Management for Positive Outcomes. 7th Edition. Singapore: Elsevier. Page 1548-1558, 1574-1576, 1582-1586

Smeltzer, C., Bare, B., Hinkle, J., and Cheever, K. (2008). Textbook of Medical-Surgical Nursing. 11th Edition. Philadelphia: Lippincott Williams and Wilkins. Page 782-787

Fauci, A., Braunwald, E., Kasper, D., Hauser, S., Longo, D., Jameson, J., and Loscalzo, J. (2009). Harrison’s Manual of Medicine. 17th Edition. New York: McGraw Hill. Pages 1388-1396

Murmurs recognition –part 1. (2009 Nov. 22). Retrieved on November 5, 2010 from http://vanumu.com/?p=728

Human Embroyology: Organogenesis. Retrieved on November 5, 2010 from http://www.embryology.ch/anglais/pcardio/umstellung01.html

Hope, I. (2010, Oct. 9). From Fetal Circulation to Pulmonary Circulation. Retrieved on November 6, 2010 from http://nursingcrib.com/nursing-notes-reviewer/maternal-child-health/from-fetal-circulation-to-pulmonary-circulation/