Patients with coronary slow flow phenomenon demonstrate normal myocardial blood flow and arterial wave reflection between acute episodes

Background: Patients with coronary slow flow (CSF) present with a syndrome (often recurrent) of resting angina with no significant coronary stenoses. The nature of myocardial blood flow (MBF), MBF reserve and systemic arterial characteristics may contribute to symptoms in these patients but this has not been examined previously. This study sought to measure MBF, arterial stiffness and wave reflection in patients with CSF and controls.
Methods: Ten patients with angiographically proven CSF and 20 controls underwent dipyridamole-exercise stress myocardial contrast echocardiography and arterial waveform analysis. MBF was quantified off-line from 10 mid and apical segments with calculation of myocardial blood volume (A), red cell velocity (β) and their product, MBF, at rest and post-stress. MBF reserve was calculated as the ratio of peak stress to resting MBF. Central arterial pressure waveforms were derived by radial tonometry, with arterial wave reflection expressed by augmentation index. Arterial stiffness was determined by aortic and brachial pulse wave velocities.
Results: There was no significant difference between CSF and control groups in mean resting β (0.56 ± 0.24 versus 0.59 ± 0.26), A (7.9 ± 1.4 versus 7.9 ± 5.2), MBF (4.3 ± 1.8 versus 4.4 ± 3.6), MBF reserve (3.7 ± 2.0 versus 4.0 ± 2.0), augmentation index (26 ± 12 versus 23 ± 9%), aortic (7.4 ± 1.8 versus 7.4 ± 1.5 m/s) or brachial (8.0 ± 0.8 versus 8.1 ± 1.3) pulse wave velocity (p > 0.4 for all). Similarly, there were no significant haemodynamic differences between groups after exercise (p > 0.2 for all).
Conclusions: MBF, large artery stiffness and arterial wave reflection characteristics are normal in CSF patients between their acute episodes.