Effect of Volume Expansion on the Anginal Threshold

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Abstract
The clinical and hemodynamic effects of rapid atrial pacing were studied in 13 patients with coronary artery disease and four normal subjects before and following acute expansion of blood volume with low molecular weight dextran. Five patients developed angina during the initial pacing period. In two of these five patients angina recurred with infusion alone, and all five of them experienced pain during the second pacing period. The anginal threshold averaged 5 min (range, 1 to 8 min) before infusion and 1.8 min (range, 0 to 5 min) following infusion. Four patients with coronary artery disease remained free of pain during the first pacing period, one of these developed pain with infusion alone, and all developed pain during pacing following infusion, the anginal threshold being 2 min (range, 0 to 3 min). The remaining four patients with coronary artery disease did not develop angina during either pacing period. Administration of dextran was accompanied by an increase in left ventricular end-diastolic pressure in all patients during sinus rhythm and during atrial pacing. Although left ventricular volume was not determined, changes in left ventricular end-diastolic pressure were interpreted as showing directional changes in left ventricular volume. Analysis of the factors affecting myocardial oxygen requirements during the two pacing periods indicated that heart rate, systemic arterial pressure, and maximal rate of rise of left ventricular pressure were similar. Although the tension-time index rose 10.6%, the major change was the increase in left ventricular end-diastolic pressure and presumably in left ventricular volume. This increase in left ventricular volume is considered responsible for the increase in myocardial oxygen requirements following infusion of dextran as determined by the decrease in the anginal threshold in each patient of the angina group.