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Possible Role of the Heart Rate for the ECG Amplitude according to the Brody Effect of Athletes and Controls H.J. Koch Dr. med. H.J. Koch Lautengasse 19 D-W-7900 Ulm (FRG) Dear Sir, In their interesting article Stor-stein et al. [ 1 ] found that there is an obvious relation between heart rate and ECG amplitudes. Apart from the anatomical configuration of the chest region, it may be advantageous to consider the current intra-cavitary blood mass of the heart. Brody [2] stated that this factor exerts an important influence on the amplitudes of ECG derivations. Experimental occlusion of the inflow tract or the outflow tract was correlated with changes in the QRS vectors [3]. Simonson [4] reported that the reduction in R-wave amplitude (lead I) during moderate exercise on a treadmill was more pronounced in a group of middle-aged men (48-58 years, n = 100) compared to young healthy men (18-28 years, n = 30) which was associated with a greater increase in heart rate. During exercise, the sympathetic acitivity was postulated to be the primary factor for the reduction in blood mass and consequently for the decrease in the amplitudes according the Brody effect [5]. On the other hand, this relations did not hold in case of coronary artery disease, ischemia or in postinfarct states [6-10]. During digitalis therapy, an increase in R-waves was observed [11], which could possibility be related to the negative chronotropic effects of these drugs. Therapy with tricyclic antidepressants, having tachycardia as a common side effect, also showed apparently a slight tendency to a reduction in the R-wave amplitude in addition to the known decrease in T-waves [12]. Many patients would profit from an improved and diversified ECG interpretation. The papers cited above support the view that the adjustment of the ECG amplitudes for heart rate should also be taken into consideration. As the authors have collected excellent data, it may be a favorable strategy for further analysis. References Storstein L, Bjornstad H, Hals O, Meen D. Electrocardiographic findings according to sex in athletes and controls. Cardiology 1991;79:227-236. Brody DA: A theoretical analysis of intracavitary blood mass influence on the heart-lead relationship. Circ Res 1956;4:731-738. Millard RW, Hodgkin BC, Nelson CV: End-diastolic volume changes reflected in the electrocardiogram. Circulation 1974;50(suppl 3):III-192. Simonson E: Effect of moderate exercise on the electrocardiogram in healthy young and middleaged men. J Appl Physiol 1953;5:384Sonnenblick EH, Braunwald E, Williams JF Jr, et al: Effects of exercise on myocardial forcevelocity relations in intact unesthetized man: Relative roles of changes in heart rate, sympathetic activity and ventricular dimensions. J Clin Invest 1965;44:2051-2061.