Published Online
on July 1, 2009

A more recent version of this article appeared on October 1, 2009

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Original Article

Short Term Memory and Restitution During Ventricular Fibrillation in Human Hearts: An In-vivo Study.

Satish C. Toal¹; Talha A. Farid¹; Raja Selvaraj¹; Vijay S. Chauhan¹; Stephane Masse¹; Joan Ivanov¹; Louise Harris¹; Eugene Downar¹; Michael R. Franz² and Kumaraswamy Nanthakumar^1,3

¹ Toronto General Hospital, Toronto, Canada;
² Veterans Affairs Medical Center, Washington, DC

³ E-mail: k.nanthakumar{at}uhn.on.ca

Background—Action potential duration (APD) variation is an important determinant of wavebreak and reentry. The determinants of APD variability during early VF in myopathic human hearts have not been studied. The objective of this study was to study the role of APD restitution and short term cardiac memory on variation in human VF.

Methods and Results—The study consisted of seven patients (67 ± 9 years old), with ejection fraction less than 35%. Monophasic action potentials (MAP) were recorded from the right and/or left ventricular septum during VF. APD_60/90 was measured in sinus beat preceding induction of VF and its amplitude was used to define 60%/90% repolarization in VF. The MAP upstroke (dV/dt_max) was used to characterize local excitability. Simple linear regression showed that variability in APD_n60 was determined by APD/DI restitution (R² = 0.48, p<0.0001) and short term memory (APD₆₀ n-1, n-2, n-3, n-4; R² 0.55, 0.40, 0.33 & 0.27 respectively, p<0.001). Using multiple step–wise regression, short term memory and restitution accounted for 62% of variance in APD₆₀ (p<0.001). Individually, memory effect had the greatest contribution to APD variability (R²=0.55, p<0.0001).

Conclusion—In early human VF, short term memory, and APD/DI restitution explain most of the APD variability, with memory effects predominating. This suggests that in early human VF, short term cardiac memory may provide a novel therpeutic target to modulate progression of VF in myopathic patients.

Key Words: electrophysiology • fibrillation • tachyarrhythmias • action potentials • sudden death