Introduction to Non-invasive Cardiology

Ronen Durst, MD

Objective

• Overview of the major non-invasive cardiac tests

– indications

– contraindications

– complications

– prognostication

Exercise Stress Testing

What do you do?

• Hook the patient up to an ECG

• Exercise the patient according to a specific protocol (Bruce, modified Bruce, Naughton, Cornell…)

• Monitor the patient during and after exercise

What is a positive stress test?

Horizontal or downsloping ST depressions

Sensitivity and Specificity

• Overall: sensitivity 68% (range 23-100%) specificity 77% (range 23-100)

• Single vessel disease: sensitivity 25-71% (LAD>RCA>Lcircumflex)

• Multi-vessel CAD: 81% (40-100%)

• (It all depends on pre-test probability)

Principles of cardiac imaging

• Need to “freeze the heart” – Breath holding– Heart beating

Imaging modalities

• Nuclear scans

• Echocardiography

• CT

• MRI

Myocardial Perfusion Imaging• Principle agents:

– Thallium– Technetium (eg sestamibi) based agents

• Image acquisition :– SPECT imaging (single photon emitted

computed tomography

Thallium is a potassium analog

• distributes proportional to blood flow and therefore cannot enter an obstructed artery

• is extracted by viable cells

• enters the intracellular K+ pool

• redistributes with time into all viable cells

How does a thallium perfusion study work?

• When a person exercises, coronary blood flow increases 3 to 5 fold. If a coronary artery is obstructed, flow across the stenosis is fixed and does not increase with exercise.

• 201Thallium is injected intravenously as thallous chloride, which then enters the blood stream and distributes in proportion to blood flow.

• It is actively taken up into viable cells as part of the potassium pool.

• Following exercise, images are made of the heart in various projections.

• Areas supplied by stenotic coronary arteries will show reduced activity.

SPECT Camera

Normal perfusion scan

Sensitivity and Specificity

• Stress testing with perfusion imaging is more sensitive and more specific than the stress-ECG.– Sensitivity: 84%– Specificity: 87%

Cardiac MRI

• Magnetic resonance imaging uses inherent cellular magnetic properties to achieve high degrees of tissue contrast

• No radiation is necessary

• Flow velocities, volumes, and gradients can be accurately calculated

Indications:

• Evaluation of the pericardium

• Evaluation of the aorta

• Congenital heart disease

• Iron overload

• Evaluation of the right ventricle

• Accurate calculation of mass and volumes

• +++

Disadvantages

• Long imaging time (getting better)

• difficult to perform in acutely ill patients

• claustrophobia

• no pacemakers or other devices

• certain types of metal are a contraindication– Ball and cage valves– staples from a cerebral aneurysm repair

Gated MRI

Multi-Detector CT

• Rapid gated acquisition of images– Heart rate has to be below 60bpm

• Data is in the form of a 3D data set

• Work in progress to develop coronary angiography and perfusion

Left atrial sarcoma

Echocardiography

Cardiac Ultrasonography

• High frequency sound waves are generated by piezoelectric crystals at frequencies of 1.5 to 16MHz or higher and formed into a beam that propagates through most body tissues.

• When this beam is reflected by a structure in the body, it bounces back to strike the crystals in the transducer, generating an electric signal.

More on echo

• The time between sending out the ultrasound wave and receiving it can be multiplied by the known velocity of that frequency of ultrasound through tissue, and the distance between the transducer and that “echo” can be determined.

• This information is then processed to form an image.

• As the speed of ultrasound in the body averages 1540m/sec, this can be repeated more than 1000/sec to generate “real-time” images.

Parasternal long axis view

Short axis view

4 chamber view

Indications for 2-D Imaging

• evaluate left ventricular wall motion• measure left ventricular size, e.g. dilatation• assess left ventricular wall thickness• visualize the valves and assess abnormalities • visualize pericardial effusions and assess size.• visualize mural thrombi or intracardiac tumors• evaluate congenital heart disease• evaluate the proximal aortic root

Doppler Echocardiography:General Principles

Aortic Stenosis

More Doppler

• Increases and decreases in the frequency of the reflected ultrasound wave can be used to calculate the velocity of red cell motion toward or away from the transducer

• This allows us to measure the velocity of flow across orifices , such as a stenotic aortic valve

Color Doppler

• Color is used to provided a 2-dimensional representation of blood flow

• This is superimposed on a 2-D image

• This can be used to assess the presence or absence of flow (eg an ASD or VSD)

• This can be used to quantify regurgitation

Mitral regurgitation

Aortic regurgitation

Endocarditis

Mitral valve prolapse

Good luck!!!!!