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QUARTERLY FOCUS ISSUE: HEART RHYTHM DISORDER: CLINICAL RESEARCH

Autonomic Nervous System Activity Measured Directly and QT Interval Variability in Normal and Pacing-Induced Tachycardia Heart Failure Dogs

Gianfranco Piccirillo, MD, PhD^_*,,_*, Damiano Magrì, MD, Masahiro Ogawa, MD, PhD, Juan Song, PhD, Voon J. Chong, Seongwook Han, MD, PhD, Boyoung Joung, MD, PhD, Eue-Keun Choi, MD, PhD, Samuel Hwang, BS, Lan S. Chen, MD, Shien-Fong Lin, PhD and Peng-Sheng Chen, MD

^_* Dipartimento di Scienze dell'Invecchiamento, Università degli Studi di Roma "La Sapienza," Rome, Italy
U.O.C. Cardiologia, Ospedale S. Andrea, Università degli Studi di Roma "La Sapienza," Rome, Italy
Krannert Institute of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
Department of Neurology, Indiana University School of Medicine, Indianapolis, Indiana

Manuscript received March 16, 2009; revised manuscript received May 28, 2009, accepted June 17, 2009.

^_* Reprint requests and correspondence: Dr. Gianfranco Piccirillo, Dipartimento di Scienze dell'Invecchiamento, I Clinica Medica, Policlinico Umberto I, Viale del Policlinico, 00161 Rome, Italy (Email: gianfranco.piccirillo{at}uniroma1.it).

Objectives: This study sought to find out more about the relationship between sympathetic and vagal nerve activity and the cardiac repolarization in a canine model of pacing-induced tachycardia congestive heart failure (CHF).

Background: The QT variability index (QTVI), a noninvasive marker of temporal cardiac repolarization dispersion, is among the risk factors for sudden death during CHF. Among factors influencing this variable are the myocardial damage and the autonomic nervous system activity typical of dilated cardiomyopathy.

Methods: We assessed autonomic nervous system activity recorded from an implanted data transmitter that monitored integrated left stellate-ganglion nervous activity, integrated vagus nerve activity, and electrocardiogram. We collected 36 segments recorded at baseline and 36 after induced CHF. We then arbitrarily identified recording segments as containing low or high sympathetic activity values, and we compared corrected QT intervals and the QTVI under a given sympathetic activity condition at baseline and after inducing CHF.

Results: In the high sympathetic activity subgroup, both QT variables increased from baseline to CHF (corrected QT intervals, p < 0.01; QTVI, p < 0.05) whereas in the low sympathetic activity subgroup they remained unchanged. The baseline QTVI correlated inversely with integrated vagus nerve activity (r² = 0.16; β = –0.47; p < 0.05) whereas, during CHF, the QTVI correlated directly with integrated left stellate-ganglion nervous activity (r² = 0.32; β = 0.27, p < 0.01).

Conclusions: During CHF, sympathetic activation is associated with an increase in the QT interval and QTVI. Because these changes vary over time, they could result from myocardial structural damage and sympathetic activation combined. Conversely, under normal conditions, no relationship exists between sympathetic activation and the QT variables.

Key Words: autonomic nervous system • QT variability index • congestive heart failure • sudden cardiac death

Abbreviations and Acronyms   ANS = autonomic nervous system   CHF = congestive heart failure   DSI = Data Sciences International   iSGNA = integrated left stellate-ganglion nervous activity   iVNA = integrate vagus nerve activity   QTc = corrected QT interval   QTm = QT mean   QTv = QT variance   QTVI = QT variability index   RRm = RR mean   RRv = RR variance   SCD = sudden cardiac death   TDR = transmural dispersion of repolarization

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