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