NORMAL STRUCTURE AND FUNCTION OF HEART

Chambers of the heart

Left atrium Left ventricle Right atrium Right ventricle

Normal Impulse ConductionSinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers

INTRODUCTION TO ECG

Meaning of ECG(Electrocardiogram): Electrocardiogram (ECG) is a graphical representation that describes about the heart activities.

Impulse Conduction & the ECGSinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers

The PQRSTP wave - Atrial depolarization

QRS - Ventricular depolarization

T wave - Ventricular repolarization

The PR Interval

Atrial depolarization + delay in AV junction(AV node/Bundle of His)

Components of ECGClick to edit Master text styles Second level Third level Fourth level Fifth level

The ECG PaperHorizontally One small box - 0.04 s One large box - 0.20 s Vertically One large box - 0.5 mV

The ECG Paper (cont)3 sec 3 sec

Every 3 seconds (15 large boxes) is marked by a vertical line.

ECG monitoring

Purpose of ECG monitoring

To assess the heart rate & rhythm. To check for ectopy (abnormal heart beat) or arrhythmia.

Placement of electrodes Note: To recall lead placement for the 3according to color coding lead system, remember white is rightand smoke over fire. The white lead goes on the right arm, and the black lead goes over the red lead on the left.

Causes of abnormal ECG patternPatients movement Loose electrodes Damaged or broken wires Improper connections Improper placement of electrodes Electrical interferences eg. Oily skin, excessive sweating, inadequate conduction jelly. Faulty equipment.

Introduction to Normal Sinus Rhythm and arrhythmias

Rhythm Analysis

Step 1: Calculate rate. Step 2: Determine regularity. Step 3: Assess the P waves. Step 4: Determine PR interval. Step 5: Determine QRS duration.

Step 1: Calculate Ratea.

Atrial rate: Count the number of small squares between two consecutive P waves and divide 1500 by this number (Rule of 1500). OR count the number of large squares between two consecutive P waves and divide 300 by this number (Rule of 300).

Contdb. Ventricular rate: Count the number of small squares between the R waves of two consecutive QRS complexes and divide 1500 by this number (Rule of 1500). OR count the number of large squares between the R waves of two consecutive QRS complexes and divide 300 by this number (Rule of 300). Note: Normally atrial and ventricular rates are identical.

Calculation of heart rate using 6 second strip:3 sec 3 sec

Count the number of R waves in a 6 second rhythm strip, then multiply by 10. 9 x 10 = 90 bpm

Step 2: Determine regularityR R

Look at the R-R distances. Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular? Interpretation?

Regular

Step 3: Assess the P waves

Are there P waves? Do the P waves all look alike? Do the P waves occur at a regular rate? Is there one P wave before each QRS? Interpretation?

Normal P waves with 1 P wave for every QRS

Step 4: Determine PR interval

Normal: 0.12 - 0.20 seconds. (3 - 5 boxes)

Interpretation?

0.12 seconds

Step 5: QRS duration

Normal: 0.08 - 0.11 seconds. (1 - 3 boxes)

Interpretation?

0.08 seconds

Rhythm Summary

Rate 90-95 bpm Regularity regular P wavesnormal PR interval 0.12 s QRS duration Interpretation? 0.08 s

Normal Sinus Rhythm

Arrhythmias

When the heart rate,rhythm,conduction or contour of any of the individual wave is abnormal,the disorder is called arrhythmia or dysrhythmia.

Arrhythmias can arise from problems in the:

Sinus node Atrial cells AV junction Ventricular cells

Arrhythmias arising in SA node

Sinus RhythmsSinus Bradycardia Sinus Tachycardia Sinus arrest.

Rate? Regularity? P waves? PR interval? QRS duration?

30 bpm regular normal 0.12 s 0.10 s

Interpretation? Sinus Bradycardia

Sinus Bradycardia

Deviation from NSR - Rate < 60 bpm

Sinus Bradycardia

Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).

Treatment: Treatment is indicated if one or more of the following signs are present: Any symptoms of decreased cardiac output or heart rate 100 bpm

Sinus Tachycardia

Etiology: SA node is depolarizing faster than normal, impulse is conducted normally. Remember: sinus tachycardia is a response to physical or psychological stress, not a primary arrhythmia.

Treatment Treat the underlying cause of tachycardia (pain, anxiety, fever etc.) If a drug overdose is suspected, adjust the dose of the drug. Notify the physician and follow the medical orders.

Sinus arrestThe condition in which SA node fails to fire is called Sinus arrest.

ARRHYTHMIAS ARISING IN ATRIA

Rate? Regularity? P waves? PR interval? QRS duration?

70 bpm occasionally irreg. 2/7 different contour 0.14 s (except 2/7) 0.08 s

Interpretation? NSR with Premature Atrial Contractions

Premature Atrial Contractions

Deviation from NSRThese ectopic beats originate in the atria (but not in the SA node), therefore the contour of the P wave, the PR interval, and the timing are different than a normally generated pulse from the SA node.

Premature Atrial Contractions

Etiology: Excitation of an atrial cell forms an impulse that is then conducted normally through the AV node and ventricles.

Treatment: Monitor the patient continuously and watch for other arrhythmias. Inform the doctor if more than 8 to 10 PACs appear per minute, and follow medical orders. If digitalis overdose is suspected, withhold the drug. Intravenous potassium may be ordered, if serum potassium level is low. Oral quinidine may be ordered for frequent PACs. Verapamil (Isoptin) may be given if PAC leads to atrial tachycardia.

NoteWhen an impulse originates anywhere in the atria (SA node, atrial cells, AV node, Bundle of His) and then is conducted normally through the ventricles, the QRS will be narrow (0.04 - 0.12 s).

Rate? Regularity? P waves? PR interval? QRS duration?

100 bpm irregularly irregular none none 0.06 s

Interpretation? Atrial Fibrillation

Atrial Fibrillation

Deviation from NSR No organized atrial depolarization, so no normal P waves (impulses are not originating from the sinus node). Atrial activity is chaotic (resulting in an irregularly irregular rate). Common, affects 2-4%, up to 5-10% if > 80 years old

Atrial FibrillationEtiology: Recent theories suggest that it is due to multiple re-entrant wavelets conducted between the R & L atria. Either way, impulses are formed in a totally unpredictable fashion. The AV node allows some of the impulses to pass through at variable intervals (so rhythm is irregularly irregular).

A re-entrant pathway occurs when an impulse loops and results in self-perpetuating impulse formation.

Treatment: The most commonly used drugs are digitalis and verapamil. Elective cardio version is required in selected cases.

Rate? Regularity? P waves? PR interval? QRS duration?

70 bpm regular flutter waves none 0.06 s

Interpretation? Atrial Flutter

Atrial Flutter

Deviation from NSRNo P waves. Instead flutter waves (note sawtooth pattern) are formed at a rate of 250 - 350 bpm. Only some impulses conduct through the AV node (usually every other impulse).

Atrial Flutter

Etiology: Reentrant pathway in the right atrium with every 2nd, 3rd or 4th impulse generating a QRS (others are blocked in the AV node as the node repolarizes).

Treatment: Treatment is required if any one of the following signs and symptoms are present: Systolic blood pressure is 80 to 90 mm Hg. or less. Weak or absent pulse Pale, cold and clammy skin Confusion and unconsciousness of patient Drug treatment consists of digoxin and/or propranolol In resistant cases, synchronized D.C. shock (elective cardio version) may be required.

Arrhythmias arising in Ventricles

Rate? Regularity? P waves? PR interval? QRS duration?

60 bpm occasionally irreg. none for 7th QRS 0.14 s 0.08 s (7th wide)

Interpretation? Sinus Rhythm with 1 PVC

PVCs(Premature Ventricular Contractions)Deviation from NSR Ectopic beats originate in the ventricles resulting in wide and bizarre QRS complexes. When there are more than 1 premature beats and look alike, they are called uniform. When they look different, they are called multiform.

PVCs

Etiology: One or more ventricular cells are depolarizing and the impulses are abnormally conducting through the ventricles.

Treatment Monitor the patient continuously for the development of lethal arrhythmias. If PVCs are associated with bradycardia, the heart rate should be accelerated by the administration of atropine or by pacing. If bradycardia is not present, IV lidocaine is given -50 to 100mg bolus, followed by an IV infusion at a rate of 2 to 3 mg/minute.

NoteWhen an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

Ventricular Conduction

NormalSignal moves rapidly through the ventricles

AbnormalSignal moves slowly through the ventricles

Rate? Regularity? P waves? PR interval? QRS duration?

160 bpm regular none none wide (> 0.12 sec)

Interpretation? Ventricular Tachycardia

Ventricular Tachycardia

Deviation from NSRImpulse is originating in the ventricles (no P waves, wide QRS).

Ventricular Tachycardia

Etiology: There is a re-entrant pathway looping in a ventricle (most common cause). Ventricular tachycardia can sometimes generate enough cardiac output to produce a pulse; at other times no pulse can be felt.

Treatment: Intravenous lidocaine 50 to 100 mg given as IV bolus and followed by intravenous infusion at a rate of 2-3mg/minute is the treatment of choice. Other useful drugs are intravenous phenytoin and procainamide. In critically ill patients, or when the drug therapy is unsuccessful, cardioversion (synchronized DC shock) is the treatment of choice. Sometimes, the ventricular tachycardia can be terminated by striking the patients chest (over the lower part of the sternum) with a closed fist (thumpversion)

Rate? Regularity? P waves? PR interval? QRS duration?

none irregularly irreg. none none wide, if recognizable

Interpretation? Ventricular Fibrillation

Ventricular Fibrillation

Deviation from NSRCompletely abnormal.

Ventricular Fibrillation

Etiology: The ventricular cells are excitable and depolarizing randomly. Rapid drop in cardiac output and death occurs if not quickly reversed

Treatment: Cardio-pulmonary resuscitation (CPR) should be initiated within seconds. The treatment of choice ( infact, the only specific treatment) is electrical defibrillation.

Ventricular Asystole

Etiology: Lethal arrhythmias. Eg: Ventricular fibrillation. Cardiogenic shock or heart failure Complete heart block. Hyperkalaemia

Treatment: Cardio-pulmonary resuscitation (CPR) is the treatment of choice which should be initiated within seconds. Electrical defibrillation should be carried out promptly, if the required apparatus (defibrillator) is available.

ARRHYTHMIAS ARISING IN

AV Nodal Blocks1st Degree AV Block 2nd Degree AV Block, Type I 2nd Degree AV Block, Type II 3rd Degree AV Block

Rate? Regularity? P waves? PR interval? QRS duration?

60 bpm regular normal 0.36 s 0.08 s

Interpretation? 1st Degree AV Block

1st Degree AV Block

Deviation from NSRPR Interval > 0.20 s

1st Degree AV Block

Etiology: Prolonged conduction delay in the AV node or Bundle of His.

Treatment: The causative factor must be identified and appropriately treated. No special measures are required for first degree A.V. block itself.

Rate? Regularity? P waves? PR interval? QRS duration?

50 bpm regularly irregular normal, but 4th no QRS lengthens 0.08 s

Interpretation? 2nd Degree AV Block, Type I

2nd Degree AV Block, Type I

Deviation from NSRPR interval progressively lengthens, then the impulse is completely blocked (P wave not followed by QRS).

2nd Degree AV Block, Type I

Etiology: Each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse (usually the 3rd or 4th) fails to make it through the AV node.

Treatment: No treatment is necessary if the heart rate remains near normal. However, the causative factor, if any, should be treated.

Rate? Regularity? P waves? PR interval? QRS duration?

40 bpm regular normal, 2 of 3 no QRS 0.14 s 0.08 s

Interpretation? 2nd Degree AV Block, Type II

2nd Degree AV Block, Type II

Deviation from NSROccasional P waves are completely blocked (P wave not followed by QRS).

2nd Degree AV Block, Type II

Etiology: Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His.

Treatment: Treatment is indicated if symptomatic bradycardia exists. Artificial cardiac pacing usually required. The drug treatment includes those drugs that increase the heart rate such as atropine, isoproterenol etc.

Rate? Regularity? P waves? PR interval? QRS duration?

40 bpm regular no relation to QRS none wide (> 0.12 s)

Interpretation? 3rd Degree AV Block

3rd Degree AV Block

Deviation from NSRThe P waves are completely blocked in the AV junction; QRS complexes originate independently from below the junction.

3rd Degree AV Block

Etiology: There is complete block of conduction in the AV junction, so the atria and ventricles form impulses independently of each other. Without impulses from the atria, the ventricles own intrinsic pacemaker kicks in at around 30 45 beats/minute.

Treatment: Drugs to accelerate heart rate include atropine and isoprenaline. Temporary urgently. pacemaker is indicated

RememberWhen an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

Critical care nurses responsibilities in monitoring and interpreting ECGRecognize and identify the type of arrhythmia. Inform the physician as necessary. Never consider any arrhythmias as unimportant. Always try to correlate ECG changes with physical signs and symptoms of the patient before taking any decisions.

ContdExamine the patient at regular intervals. Record the rate and rhythm of the heart beat at frequent intervals (through ECG strips).This is particularly important after drug therapy is initiated.

ContdWatch for other complications secondary to arrhythmia, such as fall in blood pressure, cyanosis etc.Inform the physician at the earliest. If toxicity of the drug is suspected as the cause of arrhythmia, further dosage of the drug should be withheld until approved by the physician. .

ContdAlways keep ready emergency drugs and resuscitation equipment near the patient. See that the equipments are in working condition Never leave the patient unattended. Reassure the patient.

ContdGive adequate information to the patients relatives. Always apply simple measures first, eg.a patient in pain or anxiety may develop sinus tachycardia. The nurses primary responsibility is to observe the patient for any underlying causes and remove the same as far as possible.

Thank you