Effect of physiological mechanical perturbations on intact human myocardial repolarization

doi:10.1016/S0008-6363(99)00261-8

Cardiovascular Research 2000 45(2):303-309; doi:10.1016/S0008-6363(99)00261-8
© 2000 by European Society of Cardiology

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Effect of physiological mechanical perturbations on intact human myocardial repolarization

Kumar Nanthakumar, Paul Dorian, Miney Paquette, Stuart Hutchison, Janice Andrews and David Newman^*

Division of Cardiology, St. Michael's Hospital, University of Toronto, 30 Bond Street, Toronto, Ontario, Canada M5B 1W8

^* Corresponding author. Tel.: +1-416-864-6066; fax: +1-416-864-5283 newmand{at}smh.toronto.on.ca

Objective: The objective of this study was to investigate therelationship between acute decreases in right ventricular volumeduring Valsalva strain (with resultant changes in autonomicneural tone) and measures of local endocardial repolarizationtime independent of heart rate and autonomic neural tone. Methods:Patients implanted with a stimulus to T wave (Stim-T) sensingpacemaker specially adapted to output a validated measure ofbeat to beat local repolarization (n=9) performed Valsalva manoeuvers(40 mmHg for 15 s) while paced at a cycle length of 500 ms.Stim-T intervals were measured before and after autonomic blockade(Block: 0.03 mg/kg i.v. atropine±0.15 mg/kg propranolol).Right ventricular end diastolic volume was estimated by simultaneous2D-echocardiography. Results: Without autonomic blockade, comparedto baseline, repolarization significantly prolonged during Valsalvastrain (1.1±0.7%) and shortened during release (–1.4±1.0%).After block, strain related repolarization prolongation wasalso observed (1.0±0.6%), with significantly less releaserelated repolarization shortening (–0.8±0.8%) comparedto pre-block (P<0.05). Right ventricular end diastolic volumedecreased during strain by 11±10 and 9±16% frombaseline, pre- and post-block respectively (P<0.05). Conclusion:In a chronically instrumented human model, an acute physiologicvolume reduction modestly prolongs right ventricular repolarizationindependent of changes in rate or autonomic tone.

KEYWORDS Pacemaker/AICD; Autonomic nervous system; Stretch/m-e coupling; Ventricular arrhythmias; Ventricular function

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