A proposal of clinical ECG index "vagal score" for determining the mechanism of paroxysmal atrioventricular block

Abstract

Background: Paroxysmal atrioventricular block (P-AVB) is a well-known cause of syncope; however, its underlying mechanism is difficult to determine. This study aimed to evaluate a new ECG index, the "vagal score (VS)," to determine the mechanism of P-AVB.

Methods: We evaluated the VS in 20 patients with P-AVB (13 men, 7 women; aged 25-78 years [mean, 59.3 years]). The VS was developed by assigning 1 point each for the following: (1) no AVB or intraventricular conduction disturbance on the baseline ECG, (2) PR prolongation immediately before P-AVB, (3) sinus slowing immediately before P-AVB, (4) initiation of P-AVB by PP prolongation, (5) sinus slowing during ventricular asystole, and (6) resumption of AV conduction with PP shortening, and by assigning -1 point each for (7) the initiation of P-AVB by a premature beat, and (8) resumption of AV conduction by an escape beat. Based on the clinical situations and electrophysiologic findings, we considered the mechanism of P-AVB as vagally mediated or intrinsic conduction disease (ICD).

Results: The VS ranged from 5 to -2 points for each patient. Five patients with a definite vagally mediated P-AVB had high VSs (3-5 points). We observed characteristic ECG findings of ICD consisting of changes in AV conduction by an extrasystole and/or escape beat in only 5 of the 6 patients (83%) with a low VS (1 to -2).

Conclusions: The VS is simple and potentially useful for determining the mechanism of P-AVB. P-AVB with a VS ≥3 strongly suggested a vagally mediated mechanism.

Keywords: Electrocardiogram (ECG); Intrinsic conduction disease; Mechanism; Paroxysmal atrioventricular block; Vagally mediated.

Fig. 1

Episode in case 1. Paroxysmal atrioventricular block (P-AVB) was induced during the head-up tilt test . The vagal score (VS) was 5 points: normal baseline ECG, PR prolongation and sinus slowing immediately before P-AVB, initiation of P-AVB by PP prolongation, and sinus slowing during ventricular asystole.

Fig. 2

Episode in case 5. Swallowing induced paroxysmal atrioventricular block (P-AVB) (upper ECG), which was inhibited after an administration of intravenous atropine (lower ECG). The vagal score (VS) was 3 points: sinus slowing just before and during P-AVB, and the initiation of P-AVB by PP prolongation.

Fig. 3

(A) Episode in case 15. Baseline ECG showed the first-degree atrioventricular block (AVB). Paroxysmal AVB (P-AVB) was recorded on the ECG monitoring with a long asystole of 16.5 . The vagal score was 1 point: sinus slowing immediately before P-AVB and the initiation of P-AVB by PP prolongation but the resumption of AV conduction by a junctional escape. (B) Electrophysiologic study (EPS) findings in case 15 EPS revealed a prolonged AH interval of 330 ms and a normal HV interval of 45 ms. The cessation of rapid atrial pacing of 200 bpm induced paroxysmal atrioventricular block with an asystole of 16.5 s. During a long asystole, sinus acceleration was observed and AV conduction was resumed by a ventricular escape.

Fig. 4

Episode in case 20. Baseline ECG showed a trifascular block pattern: first-degree atrioventricular block (AVB) with right bundle branch block and left axis deviation. The vagal score (VS) was –2: initiation of paroxysmal AVB by a ventricular premature beat and the resumption of AV conduction by a ventricular escape.

Fig. 5

Episode in case 8. The patient had a trifascular block, first-degree atrioventricular block (AVB) with right bundle branch block and left axis deviation, on the baseline ECG. The vagal score (VS) was 3 points: PR prolongation just before paroxysmal AVB, sinus slowing during ventricular pause, and the resumption of AV conduction with PP shortening.