After a myocardial infarction the prognosis of the patientis dependent on the success of treatment of the complicationsdescribed above, the likelihood of recurrence orextension of the infarct, and the extent of eventual impairmentof cardiac function. Despite modern advances inmedicine, some 40% of myocardial infarction victims diewithout reaching the hospital. In the prethrombolytic era the introduction of coronary care units resulted in an approximate halving of hospital mortality rates from about30% to about 15%, and the predominant cause of deathchanged from fatal arrhythmias to heart failure.After surviving an acute myocardial infarction, theprognosis is dependent on:
1. The extent of ventricular impairment
2. The propensity to life-threatening arrhythmia
3. The possibility of further infarction.
The extent of left ventricular dysfunction is dependent on:
• The state of left ventricular function prior to theinfarction
• The size and nature of the infarction
• The subsequent repair and remodelling processes
• The amount of viable myocardium still in jeopardyfrom ischaemia (inadequate blood supply and cardiacmyocytes functioning in energy deficit), stunning (reasonableblood supply but myocyte contraction impaired)or hibernation (reduced blood supply but myocytesdownregulated so as not to be in energy deficit).Thus, patients with diminished starting numbers of cardiacmyocytes (due to either previous myocardial infarctionsor old age
– secondary to natural attrition of myocytes,which averages about 35% from the age of 18 to 90 years,or previous cardiomyopathy) or pre-existing ventriculardysfunction from any cause (e.g. valvular or hypertensiveheart disease) would not tolerate the same myocardialinfarction as well as those with normal or athletic hearts.Obviously, patients incurring a larger myocardial infarctionare likely to have a worse prognosis than those with asmaller infarction. T
he repair processes post infarctionmay be impaired (e.g. by concomitant therapy with corticosteroidsor NSAIDs), leading to a greater likelihood ofinfarct expansion and ventricular aneurysm formation,resulting in a ventricle that functions less well than onewith normal scar tissue formation.The most important long-term prognostic indicator isleft ventricular dysfunction. The clinical diagnosis of heartfailure is a good indicator of dysfunction; patients withheart failure post infarction have 2-4 times greater mortalityrates than those without.
The simplest measurementsof dysfunction are left ventricular ejection fraction or endsystolicvolume, the depression of which has been found tocorrelate with mortality. These patients deserve a moreaggressive approach to treatment, in terms of risk factorreduction, ACE inhibition and, if indicated, revascularization(see below).The presence of arrhythmias at rest or during exertionis an adverse prognostic indicator after myocardial infarction.
Arrhythmias can be identified by Holter monitoring,exercise tests or direct electrophysiological studies. Frequentventricular ectopics or inducible ventricular tachycardiaare predictive of sudden death. Late potentials inaveraged ECGs and reduced heart variability are alsopredictive of life-threatening arrhythmias. High-grade AV block and bundle branch block resulting from myocardialinfaction are associated with a poor outcome.
Residual myocardial ischaemia, as manifested by postinfarctionangina or positive exercise tests, is an importantpredictor of reinfarction and mortality. High-grade stenosisor occlusion of the infarcted related artery supplying alarge portion of the left ventricle is an independent prognosticindicator.
Much prognostic information can be obtained from clinicaldata and non-invasive investigations (e.g. ECG, chestX-ray, exercise tests, echocardiography) and, if indicatedby these, more sophisticated or invasive investigationsmay then be performed. It is important to point out that,although various parameters may be predictive of prognosis,this does not imply that therapeutic attemptsto improve these parameters necessarily lead to benefits topatients or improved outcome. A rational approach tomanagement is required.