In addition to blood and biochemical tests, the listed diagnostic tests, provide valuable information to the physician in diagnosing and treating heart disease. Currently used tests include :
The last mentioned test of coronary angiography is often referred to as Invasive test, since it is an invasive procedure. All other tests are Non-invasive. A brief description including limitations is provided for our readers.
This is well established doagnostic tool known for last seventy five years.
The important criteria that are looked at are :
The test is positive most commonly in myocardial ischemia such as angina, unstable angina, and silent or latent ischemia. However, the exercise test can also be positive in about 20% of patients who are not suffering from myocardial ischemia. The non- ischemic conditions in which it can be "False Positive" include patients with hypertension ( even mild), mitral valve prolapse, certain medications, left ventricular hypertrophy, bundle branch block ( including the relatively benign right bundle branch block), cardiomyopathy, patients with expanded weak lungs due to smoking or chronic bronchial asthma and also some normal young adults and even middle aged females. In all the above enumerated non-ischmemic conditions, a negative exercise test would provide better information for the absence of anatomical myocardial ischemia. The positive test if present may be " false " or otherwise. These are an important limitations of this test which must be given due recognition. The doctor has to make its interpretation intelligently by considering all ischemic criteria, including those of his patientís symptoms or signs. If this is not done, then this test can be extremely misleading . Inspite of all this established knowledge, many exercise laboratories still report with a fixed mind set. The common words used are " The test is positive for an ischemic response." , a loaded statement for our Indian doctor-patient environment. This is undesirable way of reporting by somebody who has not studied the patientís clinical background. The common criteria for a positive test consist of ST segment depressions. The ST depressions both for ischemic and non-ischemic conditions look similar and there is no way by which a tread mill test can by itself differentiate between the two. The hasty or loose reporting in our country can give a permanent cardiac neurosis to the patient which is not justified. Our request to the exercise laboratory has been to report the test as "negative" or "positive ". If positive, then the degree of positivity be described as mild, moderate or severe. The type and degree of ST segment depression, their time of occurrence and their duration may also be elaborated upon. The final diagnosis of ischemic or non-ischemic response should be left to the treating clinician in order to avoid a pitfall.
It would be risky to perform this test in patients with recent onset angina or unstable angina. It would be wiser to wait for about 2 to 3 weeks. If done earlier it can precipitate a heart attack or life threatening heart rhythm disorder. Similarly it should be avoided in patients with severe hypertension or cardiac enlargement where it can lead to acute left ventricular failure or cerebral stroke.
Contrary to above, this test may remain negative in spite of the patient having ischemic heart disease - "False negative ". It can be negative in a patient with vasospastic angina and in a patient with single artery disease including involvement of Left anterior descending artery.
Recently, "Stress Echo" has been added to the armamentarium of tests to diagnose ischemic heart disease. It can detect ischemia by viewing abnormality in ventricular wall motion. Ischemia can be provoked with exercise or with pharmacologic agents. Pharmacologic stress echo is particularly useful in patients who cannot walk. In theory this test appears logical and at times should be more helpful than treadmill stress ( T.M.T.) to exclude misleading " False Positives " of T.M.T. . It can also help to study exercise L.V. function. In reality this test has many limitations. In order to visualize subtle wall motion abnormalities, one must have good images. This is not always possible given patient body habitus or presence of lung disease. IN addition considerable experience in scanning is required. Since this is developing technology, constant upgrading of equipment is also needed. It may turn out to be a better test in the future but at present, it has its limitations.
It can also detect wall motion abnormalities and ventricular cavity dilation. It is an objective test which can be used to assess improvement or otherwise from use of drugs. Stent Balloons or Bypass surgery.
Like all other tests, this test also has its limitations. For example, left dome of disphragm, left breast, hypertrophied left ventricle, bundle branch block, primarily dilated cardiomyopathy can interfere with correct interpretation. The degree of ischemia or its depth cannot be assessed quantitatively. It is still however, a more physiological test and is useful in several situations. The use of M.R.I., Cine CT and Positron Emission Tomography (PET) hold promise for the future.
This test is mainly useful to study abnormal fast and slow rhythm. It is indicated for a patient who presents with a syncopal attack or temporary loss of consciousness secondary to abnormal rhythms of heart.
The test is performed by introducing a catheter through one major artery in the groin ( Femoral artery). The catheter is advanced upward to reach the aorta from where Left coronary and Right coronary artery take their origin. The right and left coronaries are then selectively engaged using different catheters. Radio opaque dye is injected into left coronary artery followed by right coronary. The cine pictures are taken from different views and angles. The whole procedure is painless and takes about 30 to 45 minutes. The only painful part is the administration of the local anesthesia in the groin.
This test is generally considered safe, however since it is an Invasive procedure, it is not without risk. Possible complications include :
The above complications although rare, do occur. The risk of major complication such as a heart attack, stroke or death are about 1 in 1000. These unusual complications can be more frequent in susceptible patients with enlarged or weak hearts, hearts with complex irregularities, severe diabetes, very elderly patients.
The usual indication for angio test is only when an Invasive treatment such as Balloon Angioplasty, Stent or Bypass is seriously considered for a given patient. It is neither required nor helpful to plan for the medical management. Medical management would remain the same whether one artery is blocked or three arteries are blocked. Angiography does not help in selection of specific medical drugs. In our country, due to financial constraints and or cultural reasons patients often do not want surgery. Risk stratification for such patients can be reliable done with non invasive testing.
Coronary angiography is undoubtedly a valuable tool in cardiac diagnostics. It has been referred to by some as the " Gold Standard" test. Some reservations must be considered before making such a sweeping statement.
There is no doubt the coronary angiography is the best test available today whenever intervention such as balloon angioplasty, stent or Bypass is contemplated. It should be undertaken only after the patient has been explained about the risks and benefits before obtaining consent for the procedure.
To summarize, all the cardiac tests can be very useful provided their results are not blindly accepted. Each test has its usefulness but at the same time, every test has its limitations too. They can be of great help when interpreted intelligently. The in-depth knowledge with its proper application is the responsibility of the cardiac clinician. His role is pivotal during the process of final decision making for his patients.
Not all tests are required in every case. The attending doctor after thoroughly evaluating his patient should advise only those tests which can be really useful for a given patient which can help to further diagnose and his management problem. The doctor must use his clinical faculties to practice the " Art of Medicine " . There is really no need to "sell " all the available tests out there.