Temporal influences on the prediction of postinfarction mortality by heart rate variability: a comparison with the left ventricular ejection fraction.

Abstract

Objective-To examine the influence of the duration of follow up on the values of heart rate variability (HRV) and the left ventricular ejection fraction (LVEF) for predicting mortality after infarction. Background-HRV is an index of autonomic balance that identifies patients at a high risk of arrhythmic events. The index is most depressed during the first few weeks after myocardial infarction whereas left ventricular function tends to deteriorate with time.Hypothesis-The value of depressed HRV measured before discharge from hospital for predicting mortality after infarction should decline with time. Methods-The HRV and the LVEF were assessed in 433 survivors of a first acute myocardial infarction: HRV < 20 units and LVEF < 40% were taken as cut off points. Kaplan Within the whole follow up period, HRV < 20 units and LVEF < 40% were both strongly associated with total cardiac mortality (p < 0*0001), but HRV was an independent predictor of total cardiac mortality only during the first six months of follow up. There were no deaths predicted by HRV < 20 units after the first year of follow up whereas LVEF < 40% had a sensitivity of 43% and a positive predictive accuracy of 90/o for predicting death during this period. HRV < 20 units was better than LVEF < 40%/o in predicting sudden deaths during the first year of follow up but was an independent predictor only of those sudden deaths occurring within six months of infarction.Conclusions-The duration of follow up affects the prediction of sudden death and total cardiac mortality from HRV.Reduced HRV as measured before discharge from hospital does not seem to retain independent prognostic value after six months of follow up. These findings have potential implications for the serial evaluation of HRV and for the prevention of sudden death after myocardial infarction. (Br Heart3J 1994;71:521-527) The balance between cardiac sympathetic and vagal efferent activity is reflected in beat by beat oscillations of the cardiac cycle.' 2 The magnitude of these oscillations can be assessed by measuring heart rate variability (HRV) from ambulatory electrocardiographic recordings. As sympathetic predominance predisposes to ventricular arrhythmias, whereas vagal stimulation is protective,3 the assessment of HRV provides a means of predicting mortality after myocardial infarction,45 particularly from arrhythmic events.67The HRV is most obviously depressed during the first few weeks after myocardial infarction,8'0 whereas left ventricular function tends to deteriorate with time, particularly after extensive infarction."1 Therefore, assuming causality between sympathovagal imbalance and mortality, the predictive value of a low HRV measured early after infarction should decline with time; whereas a low LVEF before discharge from hospital should be better for predicting late mortality. The implications of this hypothesis were examined by comparing the HRV and the LVEF as predictors of mortality during different periods of follow up after a first myocardial infarction.

The Role of the Autonomic Nervous System in Sudden Cardiac Death

“…These studies were further confirmed by other in post-MI patients, showing that impaired HRV was an independent predictor of cardiac mortality only within 6 months of MI and seemed to improve over time. 70,71 That HRV improves over time is consistent with the decreasing risk of SCD after MI over a similar period. One of the largest of these trials involved 808 patients who underwent HRV analysis using 24-hour Holter monitors 11 ± 3 days post acute MI.…”

Effects of Stroke Localization on Cardiac Autonomic Balance and Sudden Death

“…24,25 Impaired HRV also is related to an increased risk of cardiac arrhythmias and to sudden death after myocardial infarction according to previous studies. 26,27 These findings may explain why stroke patients have increased susceptibility to sudden death. However, we also found that the lateralization of stroke and the involvement of the insular region had no significant effect on sympathovagal balance (LF/HF ratio) of spectral HRV, although sympathetic shift remains the same level as the control group.…”

Disfunção parassimpática, variabilidade da freqüência cardíaca e estimulação colinérgica após infarto agudo do miocárdico

“…Odemuyiwa e col 49,50 realizaram dois trabalhos em sobreviventes de IAM com seguimento após o evento agudo de cinco meses no 1º trabalho e de cinco anos no 2º. O objetivo de ambos foi comparar a sensibilidade e a especificidade da FEVE e da VFC para predição de eventos arrítmicos, morte súbita e mortalidade cardíaca total, e observaram que: a) 50% das mortes súbitas ocorreram nos seis primeiros meses; b) apesar da VFC e da FEVE serem preditores de mortalidade cardiovascular e terem sensibilidade e especificidade semelhantes para mortalidade global, a VFC é um melhor preditor de morte súbita e eventos arrítmicos nos primeiros meses (fig.…”