RESUMO
In normal individuals, heart rate in sinus rhythm varies widely in the course of a 24-hour perid, chiefly under the control of the autonomic nervous system. These flucations in heart rate can be quantified and the results are referred to as measures of "hear rate variability" [HRA]. Time and frequency domain measures of HRV reflect the balance between cardiac sympathetic and para-sympathetic tone during the recording period. This article begins by reviewing the methods and problems of measuring heart rate variability HRV is seen in patients following myocardial infarction and is a marker of adverse prognosis, especially of major arrhythmic complications. Acute myocardial infarction affects measurement of HRV. We discuss what can be deduced from abnormally low measure of HRV after infraction. Whether impaired HRV is causally related to arrhythmias or merely an epiphenomenon is then reviewed. The article shows the possible role of hear rate variability as a means of risk stratifying patients after infarction and how the technique could be combined with other tests to optimize risk production