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Paradoxical Failure of QT Prolongation During Cardioinhibitory Neurocardiogenic Syncope

1997; Elsevier BV; Volume: 79; Issue: 1 Linguagem: Inglês

10.1016/s0002-9149(96)00690-x

1879-1913

Fredrick Jaeger, Sergio L. Pinski, Richard G. Trohman, Fetnat M. Fouad-Tarazi,

Heart Rate Variability and Autonomic Control

Neurocardiogenic (vasovagal) syncope is the most common variety of syncope. Head-up tilt testing is valuable for provoking neurocardiogenic syncope in susceptible persons.[ 1 Abi-Samra F Maloney JD Fouad-Tarazi FM Castle LW The usefulness of head-up tilt testing and hemodynamic investigations in the workup of syncope of unknown origin. PACE. 1988; 11: 1202-1214 Crossref Scopus (297) Google Scholar ]Initial descriptions of the mechanisms responsible for such syncope emphasized the role of a sudden vagal discharge,[ 2 Mark AL The Bezold-Jarisch reflex revisited: clinical implications of inhibitory reflexes originating in the heart. J Am Coll Cardiol. 1983; 1: 90-102 Abstract Full Text PDF PubMed Scopus (563) Google Scholar ]but recent observations have challenged this view.[ 3 Scherrer U Vissing S Morgan BJ Hanson P Victor R Vasovagal syncope after infusion of a vasodilator in a heart transplant recipient. N Engl J Med. 1990; 322: 602-604 Crossref PubMed Scopus (150) Google Scholar ]Studies using power spectral analysis of heart rate variability,[ 4 Mizumaki K Fujiki A Tani M Shimono M Hayashi H Inoue H Left ventricular dimensions and autonomic balance during head-up tilt differ between patients with isoproterenol-dependent and isoproterenol-independent neurally mediated syncope. J Am Coll Cardiol. 1995; 26: 164-173 Abstract Full Text PDF PubMed Scopus (60) Google Scholar ]plasma catecholamine measurements,[ 5 Fitzpatrick A Williams T Ahmed R Lightman S Bloom SR Sutton R Echocardiographic and endocrine changes during vasovagal syncope induced by prolonged head-up tilt. Eur J Cardiac Pacing Electrophysiol. 1992; 2: 121-128 Google Scholar , 6 Sra JS Murthy V Natale A Jazayeri M Dhala A Deshpande S Sheth M Akhtar M Circulatory and catecholamine changes during head-up tilt testing in neurocardiogenic (vasovagal) syncope. Am J Cardiol. 1994; 73: 33-37 Abstract Full Text PDF PubMed Scopus (131) Google Scholar ]and peripheral sympathetic neural traffic[ 7 Wallin BG Sundlof G Sympthetic outflow in muscles during vasovagal syncope. J Auton Nerv Syst. 1982; 6: 287-291 Abstract Full Text PDF PubMed Scopus (287) Google Scholar ]have demonstrated complex perturbations coincident with neurocardiogenic syncope provoked by head-up tilt. The QT interval reflects the time course of ventricular repolarization. It is influenced by a multiplicity of factors, particularly the preceding RR intervals and autonomic modulation of action potential duration across the ventricular myocardium.[ 8 Ahnve S Vallin H Influence of heart rate and inhibition of autonomic tone on the QT interval. Circulation. 1982; 65: 435-439 Crossref PubMed Scopus (266) Google Scholar , 9 Cappato R Alboni P Pedroni P Gilli G Antonioli G Sympathetic and vagal influences on rate-dependent changes of QT interval in healthy subjects. Am J Cardiol. 1991; 68: 1188-1193 Abstract Full Text PDF PubMed Scopus (109) Google Scholar , 10 Zaza A Malfatto G Ravelli F Schwartz PJ Rate dependence of cardiac repolarization: autonomic modulation and interference with antiarrhythmic drug action. in: Singh BN Wellens HJJ Hiraoka M Electropharmacological Control of Cardiac Arrhythmias: To Delay Conduction or to Prolong Refractoriness. Futura, Mt. Kisco, NY1994: 57-71 Google Scholar ]We hypothesized that the QT interval would reflect the autonomic modulation occurring with neurocardiogenic syncope and serve as an “autonomic barometer.”