MISCELLANEOUS TOPICS Relation of Electrocardiographic R-Wave Amplitude to Changes in Left Ventricular Chamber Size and Position in Normal Subjects TED FELDMAN, MD, KENNETH M. BOROW, MD, ALEX NEUMANN, BS, ROBERTO M. LANG, MD, and RORY W. CHIDERS, MD Although exercise-induced changes in electrocar- diographic R-wave amplitude have been ascribed to changes in left ventricular (LV) size, QRS axis, heart rate and ischemia, the physiologic mechanism remains unclear. To clarify the relation between R-wave amptitude and changes in LV size and po- sition, simultaneous O-lead electrocardiograms and targeted M-mode echocardiograms were recorded from 15 normal subjects. Recordings were made at rest, during Valsalva maneuver and during methoxamine infusion. LV diastolic dimension in- creased with methoxamine and decreased with Vaisalva maneuver (p <O.OOl). R-wave amplitude in leads V5 and Ve varied directly with LV dimensions (p <O.OOl). The correlation coefficient between the change in R-wave amplitude in V5 or Vs and the change in LV dimension was 0.81 (p <O.OOl). No significant changes in R-wave amplttude were seen in electrocardiographic leads I, II, III, aVR, aVL, aVF or V,. Distance from the chest wall to the LV pos- terior wall correlated with change in R-wave am- plitude (r = 0.79, p <O.OOl). Change from supine to left lateral position moved the left ventricle closer to the lateral chest wall in association with a 41 f 8% .increase in R-wave amplitude in Vz and VS (p <O.OOl). In conclusion, there is a direct and a dy- namic relation between R-wave amplitude and LV chamber size. Chamber size and distance from the left ventricle to leads V5 or Ii6 interact as major determinants of R-wave amplitude. (Am J Cardiol 1985;55:1188-1174) Changes in electrocardiographic QRS amplitude have been noted during dynamic exercise. Although these changes may improve the predictive value of exercise testing for the diagnosis of coronary artery disease,1-5 their physiologic mechanism is complex. It has long been suggested that conditions that causechangesin left ventricular (LV) chamber size cause alterations in the electrocardiographic QRS complex amplitude.6 This has been inferred from the observation that QRS voltage increases after the pause following a ventricular pre- mature complex, after infusion of saline solution and during elevation of the legs. All of these maneuvers cause an increase in cardiac blood volume.6-10 This phenomenon has been linked to the Brody effect7 De- From the Cardiology Section, Department of Medicine, University of Chicago Medical Center, Chicago, Illinois. This study was supported in part by Training Grant ,2-T32-HL07381 from the National Heart, Lung, and Blood Institute, Bethesda, Maryland. Manuscript received November 9, 1984; revised manuscript received December 20, 1984, accepted December 31, 1984. Address for reprints: Ted Feldman, MD, University of Chicago Hos- pital, 950 East 59th Street, Box 250, Chicago, Illinois 60637. spite these findings, the relation between QRS complex amplitude and LV chamber size remains controver- sial.11-20 Factors such as ischemia,21QRS-axis shifts,22 or changes in intramyocardial conductioni have been suggested as major determinants of R-wave amplitude changes. During exercise, R-wave amplitude changes may be further influenced by a change in respiratory pattern, the position of the heart in the thorax and the amount of air or blood in the lungs.23 This study ex- amines R-wave amplitude changes in the absence of these confounding factors. Methods The study population consisted of healthy men, aged 21 to 33 years. All subjects had normal intracardiac anatomy and LV performance on 2-dimensional(2-D) echocardiographic study as well as a normal scalar electrocardiogram. Scalar electrocardiograms, 2-D and targeted M-mode echocardiograms, and calibrated carotid pulse tracings were recorded simultaneously from 10 subjects. Recordings were madeunder resting conditions, during Valsalva maneuver,24 and at peak pressor effect induced by the al-adrenergic ago- nist methoxamine.25*26 In 8 subjects simultaneous targeted