Detection of Rapid Changes in Ventricular Refractoriness in Human Studies

Abstract

Conventional determination of the ventricular effective refractory period (VERP) is unsuitable for detection of rapid fluctuations in the effective refractory period (ERP). A programmed stimulation system was developed that adapts continuous atrioventricular sequential pacing, incremental extrastimulus interval (S1S2) scanning, and automatic detection of extrastimulus capture which is followed by shortening of S1S2 to execute repeated scanning. The accuracy of ERP determination was tested using variable incremental (2 and 4 ms) and decremental (4-16 ms) steps of the S1S2 interval. Based on a mean of 82 determinations in eight patients, the average VERP values stayed at 249.8-251.0 ms except during the highest capture frequency. Standard deviation of ERP values ranged from 1.1 to 2.5 ms on average at the tested incremental and decremental steps. One determination was accomplished within 7.8-15.6 seconds on average. The ability to track changes in ERP was tested by changing the drive cycle length. Time constants for the adaptation rate of VERP and ventricular monophasic action potential duration at a 90% level of repolarization were determined from each test, and were similar, 51 +/- 8 seconds (mean +/- SEM) for ERP and 51 +/- 6 seconds for the action potential duration. Thus, the developed method provides accurate ERP measurements during rapid variation in ventricular refractoriness. It allows studying the recovery of excitability and the action potential duration simultaneously, and would be valuable particularly in pathological conditions and pharmacologic interventions where these electrophysiological variables become dissociated.

Atrial Refractoriness and Action Potential Duration After Sudden Reversal of Atrioventricular Sequence

“…A newly developed programmed stimulation technique was used to determine the ERP in rapid succession. The method and its validation have been described previously 19 . The system uses continuous AV sequential pacing, incremental extrastimulus interval (S1‐S2) scanning and automatic detection of capture.…”

“…The duration of MAP was measured manually from the screen display using digital ruler and calipers with 1 ms discrimination accuracy at 50% and 90% levels of repolarization. The accuracy of manual measurements has been adequate in comparison to automatic analysis of ventricular MAP duration 19 . Atrial and ventricular MAP data was obtained from the complex preceding the moment when atrial ERP was met.…”

“…The method and its validation have been described previously. 19 The system uses continuous AV sequential pacing, incremental extrastimulus interval (S1-S2) scanning and automatic detection of capture. After a determined number of drive stimuli (S1), the extrastimulus (S2) is delivered.…”

“…The accuracy of manual measurements has been adequate in comparison to automatic analysis of ventricular MAP duration. 19 Atrial and ventricular MAP data was obtained from the complex preceding the moment when atrial ERP was met. During the same cardiac cycle, the peak right atrial and systemic arterial pressures were also measured using amplitude calipers.…”

“…We examined how sudden atrial pressure load elicited by reversing the atrioventricular pacing sequence influences the electrophysiology of the atria. The adapted new stimulation system 19 allowed us to study rapid fluctuations in the atrial ERP. Simultaneously, atrial monophasic action potential (MAP) was recorded to determine the relationship of refractoriness and action potential duration.…”