Correlation Between Parameters Of Signal-Averaged Electrocardiography And The Results Of Programmed Stimulation After Myocardial-Infarction

The presence of late ventricular potentials and the induction of sustained ventricular tachycardia (SVT) by programmed ventricular stimulation (PVS) after myocardial infarction are markers of the risk of serious ventricular arrhythmias.The authors studied the value of signal averaged electrocardiography (SAECG) compared with induction of SVT by PVS in 118 consecutive patients 4 to 8 weeks after myocardial infarction. In addition to this study population, a control group of 22 patients with spontaneous SVT after myocardial infarction was also considered.Three parameters were measured after averaging 200 QRS complexes: the duration of the filtered QRS complex (QRSd), the duration of signals not exceeding 40 mu V (LAS) and the root mean square of the voltage of the last 40 milliseconds (RMS). Abnormal values were defined as: QRSd greater than or equal to 120 ms, LAS greater than or equal to 39 ms, RMS less than or equal to 20 mu V.Patients in the study population were subdivided into 3 groups: Group I (n = 17) inducible SVT; Group II (n = 72) no inducible arrhythmias; Group m (n = 29) induction of sustained ventricular ?utter or primary ventricular fibrillation requiring immediate cardioversion.The results showed a good correlation between SAECG and induction of SVT. The sensitivity (Se), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) were as follows: I) QRSd > 120 ms: Se = 82 %, Sp = 80 %, PPV = 41 %, NPV = 96 %; 2) LAS > 39 ms: Se = 59 %, Sp = 85 %, PPV = 38 %, NPV = 92 %; 3) RMS < 20 V: Se = 59 %, Sp = 88 %, PPV = 43 %, NPV = 93 %. At least one SAECG parameter was abnormal in 82 %, 26 % and 38 % of patients in Groups I, II and m respectively (p < 0,001). The left ventricular ejection fraction (LVEF) was also related to induction of SVT: Se = 65 %, Sp = 75 %, PPV = 31 %, NPV = 93 % when LEVF was < 40 %. The presence of a LVEF < 40 % and a QRSd greater than or equal to 120 ms identified 100 % of patients with inducible SVT.The authors conclude that: 1) the QRSd greater than or equal to 120 ms is the most discriminating SAECG parameter for identifying those who will have SVT on PVS performed 4 to 8 weeks after myocardial infarction (Se = 82 %, Sp = 80 %, PPV = 41 %, NPV = 96 %) and 2) the presence of a LVEF < 40 % or a QRSd greater than or equal to 120 ms enables identification of ali patients who will present SVT during PVS performed after myocardial infarction.