Distinguishing between overdrive excited and suppressed ventricular beats in guinea pig ventricular myocardium

Abstract

Rapid ventricular pacing rates induces two types of beats following pacing cessation: recovery cycle length (RCL) prolongation (overdrive suppression) and RCL shortening (overdrive excitation). The goals of this study were to compare common experimental protocols for studying triggered activity in whole-heart preparations and differentiate between recovery beats using a new methodology. Post-pacing recovery beat cycle length (RCL) and QRS were normalized to pre-paced R-R and QRS intervals and analyzed using a K-means clustering algorithm. Control hearts only produced suppressed beats: RCL ratio increased with rapid pacing (25 ± 4.0%, n = 10) without changing QRS duration. Rapid pacing during hypercalcemia + hypothermia (5.5 mM and 34°C) produced significantly earlier excited beats (53 ± 14%, n = 5) with wider QRS durations (58 ± 6.3%, n = 5) than suppressed beats. Digoxin + hypothermia (0.75 μM) produced the most excited beats with significantly earlier RCL (44 ± 3.2%, n = 6) and wider QRS (60 ± 3.1%, n = 6) ratios relative to suppressed beats. Increasing pacing further shortened RCL (30 ± 7.8%, n = 6). In a prospective study, TTX (100 nM) increased RCL ratio (15 ± 6.0%, n = 10) without changing the QRS duration of excited beats. The algorithm was compared to a cross-correlation analysis with 93% sensitivity and 94% specificity. This ECG based algorithm distinguishes between triggered and automatic activity.

Temporal response of ectopic activity in guinea pig ventricular myocardium in response to isoproterenol and acetylcholine

“…A bipolar plunge electrode in the interventricular septum was used to pace the hearts at 300 bpm for 15 s. The first recovery beat after rapid pacing was evaluated to determine if it displayed ectopic behavior (Figure 1A ). A previously established algorithm was used to stratify ectopic beats from other types by normalizing recovery beat latency and QRS width to the corresponding pre-paced intrinsic beat latency and QRS width (Greer-Short and Poelzing, 2015 ). Premature beats that occurred during pacing were also considered ectopic beats (Figure 1B ).…”