CARDIAC FUNCTION TEST

Dr. Gurumoorthi Prof. V. K. Bhatia

To assess electric and structural function

Assessment of cardiac risk is an important factor for treatment decision making in

patients with coronary artery disease

Guidelines for preoperative investigation before cardiac surgery suggest the

mandatory performance of full blood count, renal profile, ECG, chest radiograph,

and consideration of a clotting profile. Cardiac surgery patients will also need

many more specialized investigations.

Include simple non-invasive and more complicated invasive tests of cardiac

function

Non-invasive o Chest x-ray o ECG o Echocardiography o Exercise test

Invasive o Cardiac catheterizationo Thallium scanning

Tests currently used for evaluation of patients with CAD include stress

electrocardiography (ECG), stress or pharmacologic echocardiography, stress or

pharmacologic myocardial perfusion imaging (MPI), electron beam computed

tomography (EBCT), and positron emission tomography (PET)

Complete detailed clinical examination is the main part of test.

CHEST X RAY

Routine chest x-ray PA view is recommended in all cardiac surgery procedures.

It is mainly indicated in the presence of cardio respiratory symptoms or signs

Key clinical finding is heart size and pulmonary vascular flow.

Important signs associated with increased cardiac morbidity are: o Cardiomegaly …. > 50% of width of thorax in absence of valvular and

congenital disease is indicative of ventricular dysfunction.o Pulmonary edema – increased pulmonary vascular marking indicates left

ventricular dysfunction.

o Change in the cardiac outline characteristic of specific diseases.

ECG

Key clinical finding includes rate, rhythm, axis, ischemia, infarction and

hypertrophy.

Usually 12 lead ECG is used.

For preoperative assessment ECG should be taken 24-48 hours before surgery to

rule out silent ischemic changes and it also provide a base line for comparison in

operating room before induction as well as post operatively.

Resting ECG is normal in 25-50% of patients with ischemic heart disease

Characteristic features of ischemia or previous infarction may be present

Exercise ECG provides a good indication of the degree of cardiac reserve

24-hour monitoring is useful in the detection and assessment of arrhythmias [Ambulatory ECG monitoring (HOLTER]

Used to detect ECG changes during daily normal activity.

ECHOCARDIOGRAPHY

Key clinical findings are segmental wall motion, ejection fraction, valvular

function and congenital anatomic defects.

Can be performed percutaneously or transoesophageal

Two-dimensional echocardiography allows assessment of

o Muscle mass o Ventricular function / ejection fraction o End-diastolic and end-systolic volumes o Valvular function o Segmental defects

Doppler ultrasound allows assessment of valvular flow and pressure gradients

Valvular heart disease- useful in identifying type, location, severity,

physiological significance of valvular lesion, motility and thickening of stenotic

valve.

Very sensitive detector of small pericardial effusion even less than 100 ml.

Left ventricular ejection can be assessed by echo which gives a valuable

information regarding myocardial function and cardiac reserve to anesthetists.

Very useful in case of critical aortic stenosis, severe left ventricular failure or

allergy to radiographic contrast material where cardiac catherisation is not

possible.

Can find out outflow obstruction in case of hypertrophic sub aortic stenosis.

In case of ischemic heart disease it can give information regarding lack of

contraction, myocardial thinning, dilatation, post infarction ventricular septal

defect, left ventricular thrombus and aneurysm.

EXERCISE TOLERANCE TEST

For patient having pre existing and suspected CAD patients.

Multiple protocols exist for exercise tolerance tests. One common protocol

is to have the patient start walking on a treadmill and then to increase the

treadmill speed and gradient until the patient experiences symptoms or

ECG changes, heart rate, or blood pressure reaches preset limits, or the

patient reaches a predetermined metabolic workload.[ Modified Bruce

Protocol is a common regimen]

Expressed in metabolic equivalent and MET level of 5 corresponds to the

ability to perform daily activity.

Test outcomes and interpretationExercise tolerance test is strongly positive and strongly suggest of left

main or three vessel coronary artery disease when (1) systolic blood pressure falls

10 mm hg or more, (2) more than five leads show positive ST segment changes

and (3) ischemic changes occur within 3 minutes and take longer than 9 minutes

to resolve.

Electrocardiographic responses

ST-segment depression: Standard criterion for this response is horizontal or

down-sloping ST-segment depression of 0.1 mV or more for 80 milliseconds. The

probability and severity of coronary artery disease is related directly to the

amount of depression and to the down-slope of the ST segment

ST-segment elevation: In patients with no Q waves on the resting ECG,

severe transmural ischemia is signified, and the site of ischemia is pinpointed

Normal ECG during an exercise tolerance test should not necessarily be

interpreted as a negative stress test. Other outcomes, including pain, workload,

and vital sign abnormalities, are important clinical indicators as well.

No role in patients with resting ECG abnormalities (left bundle-branch block,

paced rhythm, preexcitation syndromes, or ST depressions at rest), inability to

exercise, angina, history of revascularization, medications including digoxin,

beta-blockers, vasodilators, and other antihypertensive medications.

The test is negative if the patient reaches an age-specific pre-determined heart rate

without chest pain or ST segment changes.

STRESS ECHOCARDIOGRAPHY

Stress echocardiography is used to diagnose coronary artery disease by detecting

cardiac wall motion abnormalities during exercise-induced myocardial ischemia

different exercise modalities include treadmill and supine or upright bicycle

ergometry

For patients who cannot exercise, pharmacologic echocardiography with

dobutamine incrementally increased to 20 μg/kg/min is used.

Observation of an ischemia-induced regional wall motion abnormality on

echocardiography is considered a positive test result and is graded with

respect to wall motion as normal, hypokinetic, akinetic, dyskinetic, or

aneurysmal.

Segments of the ventricle that are less than 6 mm thick, or remain akinetic or

dyskinetic despite dobutamine infusion are non-viable and represent scar

tissue

Stress echocardiography may be useful in patients with significant

cardiomyopathies for whom SPECT will be less sensitive, or in patients for

whom echocardiography is desired for other reasons and is less useful when

practitioners have limited experience performing the test.

CARDIOPULMONARY EXERCISE TEST

Non-invasive objective method of evaluating the cardiac and pulmonary

response to exercise. The patient is connected to a 12-lead ECG and

exercised on a bicycle ergometer or treadmill, whilst breathing through a

mouthpiece pneumotachograph

particularly helpful in the evaluation of cardiac failure

Table 2. Indications for pharmacologic stress echocardiography or stress SPECT

Inability to achieve exercise level sufficient for treadmill testing (ie, 85% of predicted heart rate)

Lung disease

Arthritis

Poor physical condition

Psychological impairment

Introduction of IV contrast or micro bubbles which can improve visualization

COMPUTED TOMOGRAPHY

Based on calcium present in plaque in vessel.

CT angiography is a modality that continues to improve with the

introduction of 32- and 64-slice CT scanners and may eventually equal

invasive angiography in the diagnosis of obstructing lesions.

CT Angiography is used to provide detailed information about the great

vessels (e.g. aortic dissection), in defining cardiac anatomy in patients

presenting for resternotomy (e.g. the position of the aorta in relation to the

sternum) for evaluation of cardiac function, wall motion abnormalities,

and proximal coronary artery stenosis.

Carries the risks of contrast nephropathy and high radiation exposure for the patient.

Magnetic resonance angiography High accuracy and reproducibility in the assessment of cardiac structure, function,

perfusion and myocardial viability.

Cardiac magnetic resonance angiography (MRA) allows visualization of coronary

vessels without radiation or contrast dye.

While cardiac MRI/MRA continues to evolve, it shows promise as the only

imaging modality that can combine angiography with perfusion and wall motion

assessments.

Gold standard for the assessment of ventricular mass and volume and also the

procedure of choice in the analysis of cardiac anatomy in congenital heart disease,

and the assessment of pericardial disease and intra-cardiac masses

INVASIVE METHODS

CARDIAC CATHERISATION

Gold standard in diagnosing cardiac pathology prior to open cardiac

surgery and in finding out coronary vessel pathology.

Any degree of left ventricular dysfunction, valvular abnormality, severe

pulmonary disease, impaired right ventricular function exists clinically, a

right sided [swan-ganz] catheterization is done otherwise left side is done.

A 50% reduction in vessel diameter is equivalent to a 75% reduction in

cross-sectional area, and represents a significant stenosis. Left ventricular

ejection fraction, cardiac output, pulmonary vascular resistance and end-

diastolic pressures may be measured during cardiac catheterization. In

valvular lesions, the pressure gradient or regurgitant fraction across the

valve may be estimated.

Contraindication?

PARAMETERS MEASUREMENT VALUE

Arterial or aortic pressure Systolic/diastolic <= 140/90 mm Hg

Mean <= 105 mm Hg

Right atrial pressure mean <= 6 mmHg

Right ventricular pressure Systolic/end diastolic <=30/6 mm hg

Pulmonary artery pressure Systolic / diastolic <= 30/15 mm Hg

mean <=22 mm hg

Pulmonary artery wedge Mean <=12 mm hg

Left ventricular pressure Systolic/end diastolic <=140/12 mm hg

cardiac index 2.5-402 L/min/m2

end diastolic volume index <100 ml/m2

Arteriovenous o2 content difference

<=5.0ml/dl%

Pulmonary vascular resistance

20-130 dynes sec/cm5(or)

0.25-1.6 woods units

Systemic vascular resistance

700-1600 dynes sec/cm5 or

9-20 woods units

RADIONUCLIDE PERFUSION IMAGING

used to visualize myocardial blood flow distribution using radionuclide such as

thallium and technetium

When it is combined with single-photon emission computed tomography

(SPECT), wall motion and left ventricular function can be evaluated

simultaneously.

Thallium 201 is an intracellular cation that behaves similarly to potassium and has

a half-life of 73 hours. Images are taken immediately after administration of the

thallium and again 3-4 hours later.

Technetium Tc 99m sestamibi, a calcium analogue has a shorter half-life (6 h)

Patients who are unable to exercise may undergo a thallium stress test. A common

protocol is to infuse dobutamine, 10–40 μg/kg/min

Areas of decreased blood flow and nonviable myocardium have decreased

thallium uptake and show up as defects on the initial images. Over time, the

defects related to ischemic myocardium resolve on the subsequent images as

myocardial blood flow normalizes. Persistent defects represent regions of scar

from previous MI.

A reversible perfusion defect on SPECT imaging is defined as a positive test

indicated in patients who cannot exercise and in patients for whom exercise

electrocardiography is not helpful because of resting ECG abnormalities or

exertional ST depressions associated with left ventricular hypertrophy (LVH)

Less sensitive and specific in patients with single-vessel disease (particularly

isolated disease in the circumflex artery), significant collateral formation,

cardiomyopathy, and significant attenuation from breast or diaphragm tissue.

CARDIAC TEST IN WOMEN

Women are more likely to have non obstructive or single-vessel disease when

compared with men, which decreases the diagnostic accuracy of stress testing

Calcium scoring is limited because women tend to have 3- to 5-fold greater

mortality rates for a given calcium score than men,

SPECT imaging is technically limited in women because breast tissue and

relatively small left ventricle size can generate false-positive results