Effects of atrial fibrillation on myocardial blood flow in the ischemic heart of the dog

Atrial fibrillation has a variable effect on myocardial blood flow in the intact heart. To assess its action on myocardial blood flow in the ischemic heart, measurements were made in nine dogs after ligation of the left anterior descending coronary artery before and during atrial fibrillation and with atrial pacing at the average ventricular response during atrial fibrillation. During atrial fibrillation, cardiac output decreased (from 2.4 +/- 0.2 to 1.5 +/- 0.2 liters/min, p less than 0.001) and mean aortic pressure decreased (from 90 +/- 9 to 72 +/- 7 mm Hg, p less than 0.001). Mean myocardial blood flow decreased from 63 +/- 9 to 51 +/- 9 ml/min per 100 g. Although myocardial blood flow decreased in ischemic myocardium (from 28 +/- 5 to 16 +/- 2 ml/min per 100 g, p less than 0.001), in nonischemic myocardium the changes were more variable (from 71 +/- 8 to 61 +/- 8 ml/min per 100 g, p = NS). During atrial pacing, mean and nonischemic regional myocardial blood flow were comparable with that in atrial fibrillation, whereas in the ischemic region, myocardial blood flow (20.3 +/- 3 versus 14.6 +/- 2.3 ml/min per 100 g, p less than 0.01) and left ventricular inner/outer layer ratio (0.43 +/- 0.07 versus 0.32 +/- 0.06, p less than 0.05) were lower. ST segment elevation increased with both atrial fibrillation (by 89 +/- 31%, p less than 0.05) and atrial pacing (by 51 +/- 28%). Thus, atrial fibrillation has an unfavorable influence on myocardial blood flow in the ischemic heart and worsens myocardial ischemia. This effect is at least in part due to the rapid ventricular rate.

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