Sequential changes in regional coronary flow during pacing-induced angina pectoris: coronary flow limitation precedes angina.

To investigate the sequence of changes in regional myocardial perfusion which precedes stress-induced angina, we measured great cardiac vein flow (GCVF), draining the anterior left ventricle, during incremental atrial pacing in 10 patients with normal anterior perfusion (group I) and in 11 patients with greater than or equal to 50% diameter stenosis of the left main or proximal left anterior descending coronary artery (group II). Pacing produced angina in 11 of 11 and regional lactate production in 9 of 11 group II patients. Both groups had comparable resting GCVF (group I = 62 +/- 7 ml/min vs group II = 76 +/- 9 ml/min; p = NS) and both exhibited progressive increases in GCVF with pacing. However, the entire flow-demand relationship was displaced downward in group II, as evidenced by a reduction in the percent increase in GCVF both following the first 20-beat pacing increment (group I = 46 +/- 6% vs group II = 16 +/- 4%; p less than 0.001) and at angina (group I = 113 +/- 16% vs group II = 44 +/- 9%; p less than 0.001). The first 20-beat pacing increment increased the heart rate to only 77 +/- 2 bpm in group II whereas angina and ECG changes did not occur until a pacing rate of 117 +/- 6 bpm. These data indicate that regional flow abnormalities precede the onset of pacing-induced angina in patients with coronary disease (CAD) and that these flow abnormalities frequently are detectable at heart rates substantially below the anginal threshold.