ABSTRACT
Assessment of myocardial blood flow has been the subject of extensive research and study, ever since coronary artery disease has been recognised as a first rate killer of mankind. Non-invasive methods like routine ECG, exercise ECG, 2-D echocardiography lack sensitivity and specificity. The specificity of exercise ECG becomes less in patients with ventricular hypertrophy, intraventricular conduction delay, left bundle branch block (LBBB), previous myocardial infarction, subendocardial infarction, non specific ST-T changes at rest and exercise, and electrolyte imbalance; those taking various drugs such as digitalis and quinidine; and in evaluation of post bypass graft or post PTCA (percutaneous transluminal coronary angioplasty) status. Coronary angiography, which is an invasive procedure, provides direct proof of the presence and extent of coronary artery disease in the form of anatomical changes like luminal narrowing. It fails to give any information regarding small vessel disease or bridging of vessels in the cardiac musculature and in those with normal coronaries with anginal pain at stress. It also fails to provide direct information regarding myocardial tissue perfusion, which ultimately decides the outcome of the disease. In addition, coronary angiography involves some percentage of risk to the patient. It is in this context that thallium 201 myocardial scintigraphy occupies a unique position. It has none of the disadvantages of exercise ECG and it directly reflects myocardial perfusion at the tissue level. Stress thallium 201 scintigraphy directly quantitates the amount of myocardium involved as a result of previous myocardial infarction or ischaemia, unlike stress ECG and other non-invasive modalities.(ABSTRACT TRUNCATED AT 250 WORDS)