SCRIPTA MEDICA (BRNO) – 76 (3): 141–148, June 2003 FUZZIFICATION, WEIGHT AND SUMMATION OF RISK FACTORS IN A PATIENT IMPROVES THE PREDICTION OF RISK FOR CARDIAC DEATH HONZÍK P. 1 , HRABEC J. 1 , LÁBROVÁ R. 2 , SEMRÁD B. 2 , HONZÍKOVÁ N. 3 1 Department of Control and Instrumentation, Brno University of Technology 2 First Department of Internal Medicine-Cardiology and 3 Department of Physiology, Masaryk University, Brno Abstract Patients surviving myocardial infarction are at risk of cardiac death. The predictive value of non-invasive risk factors (ejection fraction<40%, positive late potentials, a frequency of ventricular premature complexes>10/hour, baroreflex sensitivity<3ms/mmHg or low heart rate variability – SDNN index<30ms, SDANN<50 ms) is insufficient. New methods for the stratification of patients at risk were developed: 1. fuzzy method, which takes into account that the borderline between a risky and non-risky value of a risk factor is not crisp, 2. weighted method, which quantifies the significance of different risk factors, and 3. new individual indices of risk based on summation of fuzzified, and weighted risk factors respectively, (Fuzzy Sum r.f., Fuzzy-Weighted Sum r.f.) were introduced. By this method, sensitivity 44% and specificity 97% of prediction of cardiac death were reached at a positive predictive value of 50%. Key words Myocardial infarction, Cardiac death, Risk stratification, Fuzzy method, Weighted method Abbreviations used BRS, baroreflex sensitivity; c.v., critical values; EF, ejection fraction; ICD, implantable cardioverter-defibrillator device; LP, late potentials; PPV, positive predictive value; SDANN, standard deviation of 5-minute average RR intervals in 24 hours; SDNN index, mean of 5-minute standard deviations of RRs in 24 hours; VPCs, ventricular premature complexes INTRODUCTION Patients surviving myocardial infarction are at risk of cardiac death. Patients at risk can be treated with an implantable cardioverter-defibrillator device (ICD) and they must be selected carefully for this therapy. In the 90th, the non-invasive risk factors as ejection fraction - EF <40% (1), positive late potentials - LP (2), a frequency of ventricular premature complexes - VPCs >10/hour (3), a decreased heart rate variability (SDNN index – mean of 5-minute standard deviations of RRs in 24 hours <30 ms; SDANN – standard deviation of 5-minute average RR intervals <50 ms) (4) or baroreflex sensitivity - BRS <3 ms/mmHg were 141