Exercise Testing Early after Myocardial Infarction: Discussion Paper

The management of patients recovering from myocardial infarction has undergone vast changes over the last three decades. Physicians should now not merely be content that their patients have survived the acute event but try to advise them on the most appropriate longterm management. Inherent in this is the concept of risk stratification which neccessitates knowledge of the natural history of the condition, identifying which patients are at greatest risk from recurrent infarction and subsequent angina, and assessing those most suitable for medical treatment or myocardial revascularization. The natural history of myocardial infarction has been studied in several longitudinal surveys of patients admitted to hospital (Beard et al. 1960), but accurate information is obscured by the variable indications for hospital admission. These include the age of the patient and the stage and clinical state when he was seen by the general practitioner, and importantly, the home circumstances. In spite of these drawbacks, accepted statistics for outcome after infarction are a 10% six-month mortality rate (5% in the first three weeks), with about 40% of patients developing angina, a second myocardial infarction, or dying within a year (Bland & White 1941, Cole et al. 1954, Granath et al. 1977, Theroux et al. 1979). Several clinical and haemodynamic methods have been used in an attempt to identify this high-risk group. Peel et al. (1962) and Norris et al. (1969) were among the first and suggested various demographic, historical and clinical factors as prognostic indices. Only features associated with severe left ventricular impairment, however, have been found to be reproducible, and this is currently considered to be the major determinant of prognosis. Patients with a prolonged tachycardia, heart failure and a third heart sound may, therefore, be in this poor prognostic group (Wolk et al. 1972, Weber et al. 1973, Scheidt et al. 1973). The relative mortality risk, deduced from a combination of factors, has also been studied. Bigger et al. (1978) found that the strongest factors associated with mortality in the first six weeks after infarction were raised blood urea and serum creatinine levels, persistent cardiac enlargement and ventricular tachycardia two weeks after myocardial infarction, peak creatine kinase level, and left ventricular failure. The presence of one of these factors increased the risk of dying up to II times, and if two or more were present the mortality risk increased up to 20 times. The incorporation of haemodynamic data including pulmonary capillary pressure and cardiac output increased the accuracy of assessment of left ventricular function (Weber et al. 1978). The introduction of exercise tests early after myocardial infarction and their use as a prognostic guide had to await confirmation of their safety. Thirty years ago, physicians were so concerned about the possibly lethal sequelae of stressing a recently infarcted myocardium that common practice was to keep patients bed-bound in hospital for six to eight weeks. In this way the risks of damage to a presumed electrically unstable and fragile myocardium Were thought to be decreased, albeit at the expense of deep vein thromboses and often fatal pUlmonary emboli . Exercise earlier than the almost sacrosanct six weeks was thought to put the patient at risk from extension of the infarction with precipitation of serious arrhythmias, aneurysm formation or a catastrophic myocardial rupture. In 1952 Levine & Lown challenged these principles with their revolutionary ideas of