TEMPORAL INFLUENCES ON THE PREDICTION OF POSTINFARCTION MORTALITY BY HEART-RATE-VARIABILITY - A COMPARISON WITH THE LEFT-VENTRICULAR EJECTION FRACTION

Objective-To examine the influence of the duration of follow up on the values of heart rate variability (HRV) and the left ventricular eject ion fraction (LVEF) for predicting mortality after infarction. Backgro und-HRV is an index of autonomic balance that identifies patients at a high risk of arrhythmic events. The index is most depressed during th e first few weeks after myocardial infarction whereas left ventricular function tends to deteriorate with time. Hypothesis-The value of depr essed HRV measured before discharge from hospital for predicting morta lity after infarction should decline with time. Methods-The HRV and th e LVEF were assessed in 433 survivors of a first acute myocardial infa rction: HRV < 20 units and LVEF < 40% were taken as cut off points. Ka plan-Meier survival functions for total cardiac mortality and sudden c ardiac death were calculated for the whole five year follow up period and for different intervening periods. Results-During follow up of fou r weeks to five years there were 46 (10.6%) deaths and 15 (3.5%) patie nts died suddenly. Within the whole follow up period, HRV < 20 units a nd LVEF < 40% were both strongly associated with total cardiac mortali ty (p < 0.0001), but HRV was an independent predictor of total cardiac mortality only during the first six months of follow up. There were n o 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 9% for predicting death during this period. HRV < 20 unit s was better than LVEF < 40% in predicting sudden deaths during the fi rst year of follow up but was an independent predictor only of those s udden deaths occurring within six months of infarction. Conclusions-Th e duration of follow up affects the prediction of sudden death and tot al cardiac mortality from HRV. Reduced HRV as measured before discharg e from hospital does not seem to retain independent prognostic value a fter six months of follow up. These findings have potential implicatio ns for the serial evaluation of HRV and for the prevention of sudden d eath after myocardial infarction.