Signal-averaged electrocardiography: Past, present, and future

Abstract

Signal-averaged electrocardiography records delayed depolarization of myocardial areas with slow conduction that can form the substrate for monomorphic ventricular tachycardia. This technique has been examined mostly in patients with coronary artery disease, but its use has been declined over the years. However, several lines of evidence, derived from hitherto clinical data in patients with healed myocardial infarction, indicate that signal-averaged electrocardiography remains a valuable tool in risk stratification, especially when incorporated into algorithms encompassing invasive and noninvasive indices. Such an approach can aid the more precise identification of candidates for device therapy, in the context of primary prevention of sudden cardiac death. This article reappraises the value of signal-averaged electrocardiography as a predictor of arrhythmic outcome in patients with ischemic heart disease and discusses potential future indications.

Keywords: late potentials; myocardial infarction; risk stratification; syncope; ventricular tachycardia.

Figure 1

VT patient with an old anterior wall MI. From top to the bottom body surface, leads I, II, aVF, and V1, followed by endocardial electrograms from the right ventricular outflow tract (RVOT), the high right atrium (HRA), the right ventricular apex (RVA), and the left ventricular (LV) infarct zone. During the sinus rhythm, there are late fragmented and low‐amplitude signals originating in the LV infarct zone (arrow). During the VT (left side), the fragmented potentials of the LV zone prolong their duration bridging the diastolic phase of the VT cardiac cycle (arrows), disappearing upon VT termination (slow pathway conduction block)

Figure 2

SAECG from two patients. The one (right) with a history of sustained monomorphic ventricular tachycardia and the other (left) without such a history. The RMS‐40 of the filtered QRS complex is lower in the VT patient (4 vs 34 μV). The LAS‐40 duration is longer in the VT patient (78 vs 29 msec). The duration of the filtered QRS complex is also longer in the VT patient (114 vs 97 msec). RMS: root mean square, LAS: low‐amplitude signal

Figure 3

Sensitivity versus specificity plot for different LP criteria among patients with a widened QRS complex. The optimal combination of sensitivity and specificity for the sustained VT induction, despite the presence of a wide QRS (≥120 msec) complex is provided by a (A) filtered QRS and (B) LAS >145 and 50 msec, respectively, with a (C) RMS <17.5 μV Ref. (5)

Figure 4

Post‐MI patient with recurrent sustained VT and LBBB. Despite the presence of bundle branch block, LPs of long duration (LAS: 147 msec) and of very low amplitude (RMS: 8 μV) are revealed. Total filtered QRS duration: 203 msec

Figure 5

SAECG from a Naxos disease patient (left), a post‐MI patient with sustained VT (center), and a healthy control (right). LPs are revealed in the two patients being of longer duration and of lower amplitude in the Naxos disease patient Ref. (60)

Figure 6

Elimination of late potentials in the signal‐averaged electrocardiogram (SAECG) after aneurysmectomy. SAECG performed in a 64‐year‐old postmyocardial infarction patient with left ventricular aneurysm before (fQRS = 191 ms, RMS‐40 = 1 μV, LAS = 104 ms) and after (fQRS = 113 ms, RMS‐40 = 16 μV, LAS = 35 ms) aneurysmectomy of the left ventricle showing disappearance of the pre‐existing late potentials. The presenting sustained ventricular tachycardia (VT) (both spontaneous and induced preoperatively) was not induced postoperatively Ref. (61)