Key result
Short-term cardiac memory induced by constant pacing significantly decreased ventricular APD90 (252.9 vs 235.6 ms; P=0.001) and QTc, but did not change the maximal slope of APDR or QTd.
Why the study?
Does short-term cardiac memory induced by right ventricular pacing alter ventricular arrhythmogenicity in humans?
Does short-term cardiac memory induced by right ventricular pacing alter ventricular arrhythmogenicity in humans?
Absolute Event Rate: 235.6% vs 252.9%
p-value: p=0.001
Short-term cardiac memory alters ventricular repolarization by shortening APD90 and QTc, but does not significantly affect arrhythmogenicity markers such as APDR slope or QT dispersion.
CM effects on arrhythmogenicity remain hypothesis-generating in this small cohort; larger prospective studies needed before clinical relevance.
Cardiac memory (CM) can alter the configuration of action potentials and the transmural repolarization gradient in ventricular tissue. This study evaluated the effects of CM on ventricular arrhythmogenicity. A total of 20 patients (12 females, 8 males; mean age, 46 +/- 13 years) were enrolled. The following indicators were measured to evaluate ventricular arrhythmogenicity: (1) the action potential duration at 90% repolarization (APD90) recorded from the right ventricular apex (RVA); (2) the maximal slope of the action potential duration restitution curve (APDR) constructed by programmed extra stimuli from RVA; and (3) the maximal corrected QT interval (QTc) and QT interval dispersion (QTd). The short-term CM was induced by constant pacing from the RVA at a pacing cycle length (PCL) of 400 ms for 20 minutes. After induction of CM, the mean APD90 were significantly shortened at both PCLs of 600 ms and 400 ms (252.9 +/- 6.4 ms vs. 235.6 +/- 6.4 ms and 231.2 +/- 6.4 ms vs. 214.4 +/- 7.3 ms, respectively; p = 0.001). No significant change regarding the maximal slopes of APDR were found at both PCLs of 600 ms and 400 ms (1.05 +/- 0.09 vs. 0.96 +/- 0.11 and 0.85 +/- 0.08 vs. 0.84 +/- 0.09, respectively). QTc (417.3 +/- 9.1 ms vs. 454.7 +/- 8.3 ms; p = 0.001), but not QTd (63.4 +/- 5.4 ms vs. 65.7 +/- 6.1 ms), was significantly shortened. Short-term CM significantly decreased ventricular APD90 and QTc, but did not significantly change the maximal slope of APDR or QTd. These results suggest that CM might not have a significant effect on ventricular arrhythmogenicity.
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Lee et al. (2009) studied this question. Short-term cardiac memory induction via constant pacing vs. Baseline (before induction) was evaluated on Action potential duration at 90% repolarization (APD90) at a pacing cycle length of 600 ms (p=0.001). Short-term cardiac memory induced by constant pacing significantly decreased ventricular APD90 (252.9 vs 235.6 ms; P=0.001) and QTc, but did not change the maximal slope of APDR or QTd.
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