Is target heart hate an appropriate endpoint for dobutamine stress echocardiography in patients with atrial fibrillation?

Exceeding 85% of the age predicted heart rate is a routine endpoint for dobutamine stress echo (DSE). However, patients (pts) with atrial fibrillation (AFIB) may reach age predicted heart rate at doses of dobutamine that are insufficient to induce ischemia. To test this hypothesis, 29 pts, aged 72±10 yrs, with AFIB were compared to 22 pts, aged 65±13 yrs, in sinus rhythm (NSR) with + DSE and coronary artery disease (CAD) by catheterization. Resting heart rate for all AFIB and NSR pts were similar. None of the NSR pts were on medications to decrease heart rate. Among AFIB pts, 9 were on no medications to decrease heart rate, 14 were on digoxin, and 6 were on Ca⁺⁺ or β-blockers. A standard protocol up to 50 μg/kg/min dobutamine was used. Two AFIB and 9 NSR pts were also given atropine. Results are shown. Peak %Age Pred. Dobutamine Group n Heart Rate Heart Rate dose (peak) NSR: + DSE/CAD 22 140±10 87±19 38±9 AFIB: No Medications 9 158±18 * 112±8 * 23±7 * AFIB: Digoxin 14 154±20 * 101±16 * 26±9 * AFIB: Ca⁺⁺ or β-blocker 6 142±21 96±10 30±7 * (* p<0.05 vs. NSR: +DSE/CAD group) All AFIB patient groups achieved ≥ 85% age predicted heart rate at significantly lower dobutamine doses than NSR pts with + DSE/CAD. One AFIB pt on no medications who had a -DSE had a subsequent MI and severe 3 vessel CAD by catheterization 2 months later. Conclusions: AFIB pts reach age predicted heart rate with lower dobutamine doses than NSR pts with +DSE and CAD. Since a lower dobutamine dose may be insufficient to induce ischemia, the ability of DSE to detect significant CAD may be affected in pts with AFIB.