Effects of spinal cord stimulation on myocardial blood flow assessed by positron emission tomography in patients with refractory angina pectoris

Spinal cord stimulation in angina pectoris increases exercise capacity and reduces both anginal attacks and ischemic electrocardiographic signs. This suggests an anti-ischemic action, perhaps through changes in myocardial blood flow. In 9 patients, regional myocardial blood flow was studied with positron emission tomography before and after 6 weeks of spinal cord stimulation, both at rest and during a dipyridamole stress test. Frequency of anginal attacks and consumption of short-acting nitrates were assessed by patient diaries. Exercise duration and time to angina were measured with treadmill exercise tests. After 6 weeks of stimulation, both frequency of daily anginal attacks and nitrogen consumption decreased (3.7 +/- 1.7 vs 1.4 +/- 1.0 [p < 0.01] and 2.8 +/- 2.2 vs 1.1 +/- 1.2 tablets [p = 0.01], respectively); exercise duration and time to angina increased (358 +/- 165 vs 493 +/- 225 seconds [p < 0.01] and 215 +/- 115 vs 349 +/- 213 seconds [p = 0.02], respectively); and ST-segment depression during dipyridamole stress testing was reduced (0.17 [0 to 0.5] mV vs 0.09 [0 to 0.2] mV, p = 0.04) (all data mean +/- SD). Total resting blood flow remained unchanged (115 +/- 29 vs 127 +/- 31 ml/min/100 g, p = 0.31), but flow reserve decreased (146 +/- 43% vs 122 +/- 39%, p = 0.04). The coefficient of variation of flow, representing flow heterogeneity, decreased after treatment, both at rest (20.1 +/- 3.8% vs 17.4 +/- 2.6%, p = 0.04) and after dipyridamole stress (26.2 +/- 4.4% vs 22.9 +/- 5.5%, p = 0.02). Thus, spinal cord stimulation is clinically effective due to homogenization of myocardial blood flow. Since flow reserve decreases despite clinical improvement, the dipyridamole effect may be blunted by spinal cord stimulation.