ST-segment depression in atrioventricular nodal reentrant tachycardia: Important finding or just an artifact?

Abstract

Background: The ST segment is component of the QRS-T complex located between the QRS and the T wave. ST segment changes during tachycardia with narrow QRS mainly takes the form of ST segment depression. This phenomenon is often observed in young healthy people for whom an ischemic background is unlikely. Materials and methods: The study included 104 patients (71 women and 33 men) with paroxysmal narrow QRS complex tachycardia. In all patients electrophysiological study was performed and the diagnosis of atrioventricular nodal reentrant tachycardia was established. The arrhythmogenic substrate was then eliminated successfully by subsequent ablation using radiofrequency energy which confirmed the diagnosis, all patients had measured QRS components – QR, RS and RJ during the tachycardia and during the sinusrhythm. All of the measurements were done in lead V5. Results: The difference RJ-QR during tachycardia and sinus rhythm correlated negatively with tachycardia cycle length (R = 0.356, P = .001), first slowly, then rapidly reaching the cycle value of about 300 ms, then it decreases, stabilizing at the cycle level of about 270. By separating the RJ-QR in tachycardia and in the sinus rhythm from the tachycardia cycle, we can see that the correlation described in this point is largely due to the correlation between the heart rate and RJ-QR length in tachycardia. Conclusions: In patients with atrioventricular nodal reentrant tachycardia, there is a significant ST-segment depression during tachycardia episodes and the degree of this change is related to tachycardia cycle length. The most probable explanation of the ST-segment depression is the overlap of the QRS complex on the preceded T wave. This phenomenon is also influenced by some intrinsic properties of the individual electrocardiogram. It is possible to rule out ischemic origin of the presented ST segment change.

ST segment depression in atrioventricular reentrant tachycardia

“…Due to the dynamic change in the amplitude of all components of the QRS complex (QR, RS, RJ) from beat to beat, there is a change in the baseline, which may look like a depression of the ST segment. The QRS alternans in AVRT has not been explained, some studies suggest intraventricular conduction disturbances as the cause of this phenomenon [6]. In our study, unfortunately, we did not have patients with QRS alternans during orthodromic tachycardia.…”

“…The shorter the arrhythmia cycle, the greater the overlap of the T wave of the previous QRS complex with the next QRS complex, which causes a rise the baseline and may give the impression of ST segment depression. We proposed a similar explanation for the AVNRT in another article [6].…”

“…We assessed the ECG analogously to our earlier work on AVNRT [6][7]. Figure 1 shows how the individual components of the QRS complex were measured.…”