( By Dr. Natoobhai J.Shah & Dr. Sailesh N. Shah )

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b-Cardiological Tests As Used Currently

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 :

  1. Resting Electrocardiogram ( E.C.G.)
  2. Treat Mill Exercise or Bicycle Exercise Test (Exercise Stress Test)
  3. Echocardiogram including Exercise Echo
  4. Stress MUGA Study ( Nuclear Test)
  5. Stress Thallium or Sestamibi study
  6. Holter Monitoring
  7. Coronary Angiography

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.

  1. Resting Electrocardiogram ( E.C.G. or E.K.G. as abbreviated in Europe and U.S.A. )

    This is well established doagnostic tool known for last seventy five years.

    1. It is best for the diagnosis of cardiac rhythm disorders. Till today, there is nothing to surpass E.C.G. in the diagnosis of cardiac rhythm disturbances.
    2. To detect enlargement of the heart chambers such as left ventricle, right ventricle, left atria.
    3. Coronary heart disease ( Ischemic heart disease).

      1. In acute coronary thrombosis or infarction, it has proven to be a very helpful and reliable test. Almost 98% of acute infractions can be confidently diagnosed by a simple bed side resting E.C.G. , within minutes of the onset of infarction.
      2. The diagnosis of clinical angina can be made with the resting E.C.G. in only 60% of patients. In about 40% of patients with classical angina, the resting E.C.G. may remain normal any may mislead the unwary. This may also hold true in some cases of severe form of angina, known as unstable angina. IN such cases, an alternative test may be more appropriate.

  2. Exercise E.C.G. Test
    Exercise stress testing as this is often referred to, can be done using a Treadmill or a stationery bicycle. The principle of the test is to increase heart rate to a predetermined level based on the patientís age. The usual formula used to determine target heart rate is 20 (-) minus the age of the patient. If a patient is 50 years old, then target heart rate would be 220-50 = 170/minute.

    The important criteria that are looked at are :

    1. The E.C.G. change in ST segment shift
    2. Change in blood pressure, particularly its fall in blood pressure
    3. Symptoms of angina

    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.

  3. Echocardiogram
    The echocradiogram along with color Doppler study is ideal for visualization of the various cardiac structures. It plays a vital role in identifying congenital heart disease and valvular heart disease. It also has its role in the evaluation isochemic heart disease. Since the myocardium can be visualized, areas that are ischemic often contract less than adjacent non-ischemic myocardium that may be supplied by another artery. This is seen on the echo as a "hypokinetic" segment. Similarly, areas that have been infarcted appear not to move at all "akinetic" and may even appear thin and dense. The important contribution of Echo is in the assessment of contractile left ventricular function what is technically known as Left Ventricular Ejection Fraction (L.V.E.F.). The normal ejection fraction is at least 55%. Echo is also helpful is diagnosing chamber size enlargement and in diagnosing the presence of a clot in the cavity of the left ventricle.

    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.

  4. MUGA Test
    MUGA is an abbreviation for Multiple Gating. In this test, a radioactive isotope is injected which binds to the circulating red blood corpuscles ( R.B.C.0 As they circulate through the left ventricular cavity, these radioactive R.B.C.ís are rapidly gated by use of Gamma camera from multiple angles using various phases of the cardiac cycle. The patient lays down facing a Gamma camera. At first, resting cardiac study is done. This is followed by some form of Leg exercise or Hand grip exercise. Left ventricular (1) regional movements with its (2) Contractile function is assessed. This test also has several limitations in giving " False Positives " and " False Negatives " . IN spite of these, it is a more reliable test for assessment of Left Ventricular Function ( L.V.E.F.) during rest as well as exercise.

    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.

  5. Stress Thallium Scinitigraphy
    Now a days some laboratories use the new isotope sestamibi in place of Thallium. The principle of either isotope is that of entry perfusion in myocardial muscle cells. Normal healthy myocardial cells accept the dye when delivered via good patent coronary channels. With coronary obstructive disease, the afflicted myocardial cells pick up the isotope poorly and in infarcted nonviable myocardium does not pit it up at all resulting in a persistent " filling defect. " The isotope is injected during peak of moderate exercise. When exercise is not possible certain other coronary dilators such as persantin may be used. Persantin, however, does have some risk associated with its administration.

    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.

  6. 24 hour Holter Monitor study
    In this a patientís heart rhythm is recorded continuously for 24 hours, on a cassette tape. This tape is then analyzed through a rapid scanner and a printout is generated. During the period of monitoring the patient is asked to perform his regular activities, monitoring is continued through the night, since this is when heart rates tend to be the slowest.

    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.

  7. Coronary Angiography
    Coronary angiography is performed to visualize the anatomy of the major arteries, their branches and their distribution are shown on the back cover of this book.

    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 :

    1. Serious heart irregularities including cardiac arrest.
    2. Detachment of a blood clot or a plaque to lodge in the brain circulation resulting in a "stroke".
    3. Prolonged coronary spasm, coronary artery plaque rupture can on a rare occasion lead to procedure related infarction.
    4. Local complications in the groin such as bleeding, hematoma with infection, some form of aneurysm or downward dissection of the artery involving one leg.
    5. Severe reaction to the angiographic dye.

    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.

    1. Unlike reputed Gold, the information or map obtained through angiography usually holds good for an average of 6 months to a maximum of 1 year only. The constant blood flow in coronary arteries can modify the blockages in course of time. The site of blockage can also change. It may increase or even decrease with passage of time.

    2. Angiography can visualize narrowings only in major epicardial coronary arteries and their large brunches. The smaller arteries, protective mini collaterals and terminal pathways of capillaries which provide oxygen and nourishment to the cells cannot be studied. With better understanding of molecular vascular biology, the assessment of these small channels may also become important before proceeding with invasive testing

    3. Two types of Angina known as "Vasospastic Angina" and " Microvascular (syndrome ĎXí) Angina " cannot be positively diagnosed from coronary angiography.

    4. The coronary arteries are living biological active channels. By angiography, we can only see the blocks but cannot in anyway assess about the physiologic state of coronary endothelium. Nor do we get any information about the protective or otherwise local platelet activity, or the state of blood products for its anti-clotting or clotting effects.

    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.

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