Coronary flow abnormalities in hypertrophic cardiomyopathy

Abstract

Hypertrophic cardiomyopathy (HCM) affects 1 in 500 of the general population. Patients commonly suffer from angina, exhibit abnormal coronary flow patterns and have impaired myocardial perfusion. Wave intensity analysis (WIA) allows improved understanding of how myocardial mechanics result in impaired coronary flow. We used WIA to describe these mechanisms in HCM. We developed a new sequence for measurement of coronary flow velocity using cardiovascular magnetic resonance (CMR) and tested its utility for non-invasive coronary WIA. Patients with HCM had a lower coronary flow reserve than controls and 30% had systolic reversal of flow. During early systole, HCM patients had a much larger fractional backward compression wave compared to controls (38.2±11.1% versus 21.0±6.2%, p<0.001). Patients with severe left ventricular outflow tract obstruction had a bisferiens pressure waveform resulting in an additional proximally originating deceleration wave during systole. These changes correlated with the severity of myocardial perfusion impairment. Perfusion abnormalities in HCM are therefore not simply a consequence of supply/demand mismatch or remodelling of the intra-myocardial blood vessels but represent a dynamic interaction with myocardial mechanics. We developed a retrospectively-gated breath-hold spiral phase velocity mapping sequence with high temporal resolution for measurement of flow velocity in the proximal coronary arteries using CMR and validated this against invasive measurement. CMR velocities were approximately 40% of the invasive values. Plots of MR velocities at any time point in the cardiac cycle against Doppler velocities in individual vessels showed a linear relationship with high R2 values (mean ± SD: 0.8± 0.1). Combination of the velocity data with pressure data derived from aortic distension produced the expected pattern of forward and backward compression and expansion waves seen in coronary arteries with comparable intra-study reproducibility to invasive WIA. Although only tested in small numbers, if validated this technique would expand the accessible patient population for WIA.