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CLINICAL STUDY: ELECTROPHYSIOLOGY

The repolarization-excitability relationship in the human right atrium is unaffected by cycle length, recording site and prior arrhythmias

Frank Bode, MD^* , Michael Kilborn, MD^*, Pamela Karasik, MD, FACC^* and Michael R. Franz, MD, PhD, FACC^*

^* Veteran Affairs Medical Center and Georgetown University, Washington, DC, USA
Medizinische Klinik II, Universitaetsklinikum, Luebeck, Germany

Manuscript received December 3, 1999; revised manuscript received October 6, 2000, accepted November 17, 2000.

Reprint requests and correspondence: Dr. Michael R. Franz, Cardiology Division, Veteran Affairs Medical Center, 50 Irving St., NW, Washington, DC 20422
mfranz{at}washington.va.gov

OBJECTIVES

The goal of this study was to determine the relationship between repolarization and excitability in the human atrium under various conditions.

BACKGROUND

Action potential duration (APD) measurements from monophasic action potential (MAP) recordings provide a surrogate for measuring the effective refractory period (ERP) in human ventricle. The relationship between repolarization and refractoriness in human atrium and the effect of prior atrial fibrillation/flutter on the ERP/APD correlation are unknown.

METHODS

Seven patients with sinus rhythm and 15 patients after conversion of atrial flutter or fibrillation were evaluated. Monophasic action potentials were recorded at multiple right atrial sites and during different basic cycle lengths from 300 to 700 ms, while ERPs were determined by extrastimulus technique using the MAP recording-pacing combination catheter.

RESULTS

There was a close correlation between ERP and APD at 70% repolarization (APD₇₀, r = 0.97; p < 0.001) and 90% repolarization (APD₉₀, r = 0.98; p < 0.001), respectively. Refractoriness occurred at a repolarization level of 72 ± 8%. The ERP/APD₇₀ and ERP/APD₉₀ ratios averaged 1.06 ± 0.10 and 0.86 ± 0.08, respectively. These ratios were nearly constant over the entire range of basic cycle lengths, between different sites in individual patients and between different patients. Patients cardioverted from atrial fibrillation or flutter exhibited no significant differences in the ERP/APD relationship compared with patients with sinus rhythm.

CONCLUSIONS

Effective refractory period and APD are closely related in the human right atrium. Using the MAP recording technique, atrial ERPs can be assessed by measurement of APDs. Effective refractory period is most closely reflected by APD₇₀. Thus, MAP recordings allow investigation of the local activation and repolarization time course beat by beat, visualizing the excitable gap.

Abbreviations and Acronyms   APD = action potential duration   APD70 = action potential duration at 70% repolarization   APD90 = action potential duration at 90% repolarization   ERP = effective refractory period   MAP = monophasic action potential

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