Signal-Averaged Electrocardiogram: Update 1997

The effect of myocardial surgical revascularization on left ventricular late potentials

BACKGROUND

The presence of ventricular late potentials (LP) is an important indicator for the development of ventricular tachyarrhythmias due to ischemic heart disease. The effect of myocardial revascularization on LP has remained controversial. The purpose of this study was to determine whether complete myocardial surgical revascularization (CABG) documented by myocardial perfusion scintigraphy might alter the substrate responsible for LP.

METHODS

Prospectively, enrolled patients undergoing elective CABG were evaluated with thallium-201 myocardial perfusion scintigraphy and signal- averaged ECG pre- and postoperatively. SAECG recordings were obtained serially: before, 48-72 hours and 3 months after CABG. LPS were defined as positive if SAECG met at least two of Gomes criteria. Scintigraphies were performed pre- and 3 months postoperatively for determination of the success of revascularization. Changes observed in SAECG recordings after CABG were compared between those with and without successful revascularization.

RESULTS

CABG resulted in successful revascularization in 23 patients and was unsuccessful in 17 (no change or deterioration of the perfusion defects). Preoperative SAECG values were not different between groups except for RMS values. The incidence of LP decreased significantly postoperatively in patients with improved myocardial perfusion, whereas there were no changes in patients who did not have postoperative perfusion improvement (McNemar test, P < 0.05).

CONCLUSIONS

LPs disappear following the elimination of myocardial ischemia by complete surgical revascularization. Persistence of ischemia following CABG usually results in the persistence of late potentials. The incidence of ventricular arrhythmias is expected to be unchanged in these patients and they should be reevaluated for reinterventions.

The effect of statin therapy on ventricular late potentials in acute myocardial infarction

AIMS

To determine whether early statin therapy in acute myocardial infarction has any effect on ventricular late potentials which are considered as a noninvasive tool for evaluation of arrhythmogenic substrate.

METHODS AND RESULTS

Study population consisted of prospectively enrolled 72 patients presenting with acute myocardial infarction (<6 h). Thirty-four of the patients were randomized to pravastatin (40 mg/day) on admission irrespective of lipid levels. All patients received thrombolytic therapy. Signal-averaged ECG recordings were obtained serially prior to thrombolytic therapy, 48 h after and 10 days later. Late potentials were defined as positive if signal-averaged ECG met at least two of Gomes criteria: filtered total QRS duration >114 ms, root mean square voltage of the last 40 ms of the QRS <20 mV, or the duration of the terminal low (<40 mV) amplitude signals >38 ms. Changes observed in signal-averaged ECG recordings after thrombolysis were evaluated statistically with regard to statin usage. There were no significant differences between the clinical characteristics of the two randomized groups. There was a significant decrease in the rates of late potentials between the first and third signal-averaged ECG recordings after thrombolytic therapy in pravastatin group. Pravastatin group also had lower incidence of ventricular arrhythmias compared with control group (26 vs. 63%, P=0.021). The in-hospital cardiovascular event rates were also lower in statin group.

CONCLUSION

Early use of pravastatin reduces the incidence of late potentials following thrombolytic therapy in acute myocardial infarction. Statin therapy also seems to be reducing the incidence of in-hospital ventricular arrhythmias. These beneficial effects of statins might be explained through prevention of new myocardial ischemic episodes due to early plaque stabilization or regulation of endothelial and platelet functions.