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Mechanisms of Myocardial Ischemia in Hypertrophic Cardiomyopathy: Insights From Wave Intensity Analysis and Magnetic
Claire E Raphael1, Robert Cooper2, Kim H Parker3
1NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, United Kingdom.
Insights
Abnormal heart mechanics in hypertrophic cardiomyopathy (HCM) cause reduced coronary flow and myocardial perfusion. Wave intensity analysis reveals unique pressure wave patterns contributing to ischemia in HCM patients.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Cardiac Imaging
Background:
- Angina is a common symptom in hypertrophic cardiomyopathy (HCM).
- Abnormal myocardial perfusion is frequently observed in HCM patients.
- Wave intensity analysis offers insights into the mechanics of myocardial ischemia.
Purpose of the Study:
- To elucidate the mechanisms of perfusion abnormalities in HCM using wave intensity analysis.
- To characterize coronary hemodynamic alterations in HCM patients.
Main Methods:
- Simultaneous pressure and flow measurements in the left anterior descending artery of 33 HCM patients and 20 controls.
- Wave intensity calculations at rest and during hyperemia.
- Quantitative first-pass perfusion cardiac magnetic resonance to assess myocardial perfusion reserve.
Main Results:
- HCM patients exhibited lower coronary flow reserve compared to controls (1.9 vs. 2.7, p=0.01).
- HCM patients showed significantly larger systolic backward compression waves (38% vs. 21%, p<0.001) and smaller backward expansion waves (27% vs. 33%, p=0.006).
- Severe left ventricular outflow tract obstruction was associated with an additional systolic deceleration wave.
Conclusions:
- Coronary flow derangements in HCM involve abnormal systolic backward compression waves and, in some cases, deceleration waves due to outflow tract obstruction.
- Perfusion abnormalities in HCM are complex, involving dynamic interactions with ischemia mechanics, not solely supply/demand issues or vessel remodeling.
- These findings suggest potential therapeutic targets for improving myocardial ischemia in HCM.
Background:
Angina is common in hypertrophic cardiomyopathy (HCM) and is associated with abnormal myocardial perfusion. Wave intensity analysis improves the understanding of the mechanics of myocardial ischemia.
Objectives:
Wave intensity analysis was used to describe the mechanisms underlying perfusion abnormalities in patients with HCM.
Methods:
Simultaneous pressure and flow were measured in the proximal left anterior descending artery in 33 patients with HCM and 20 control patients at rest and during hyperemia, allowing calculation of wave intensity. Patients also underwent quantitative first-pass perfusion cardiac magnetic resonance to measure myocardial perfusion reserve.
Results:
Patients with HCM had a lower coronary flow reserve than control subjects (1.9 ± 0.8 vs. 2.7 ± 0.9; p = 0.01). Coronary hemodynamics in HCM were characterized by a very large backward compression wave during systole (38 ± 11% vs. 21 ± 6%; p < 0.001) and a proportionately smaller backward expansion wave (27% ± 8% vs. 33 ± 6%; p = 0.006) compared with control subjects. Patients with severe left ventricular outflow tract obstruction had a bisferiens pressure waveform resulting in an additional proximally originating deceleration wave during systole. The proportion of waves acting to accelerate coronary flow increased with hyperemia, and the magnitude of change was proportional to the myocardial perfusion reserve (rho = 0.53; p < 0.01).
Conclusions:
Coronary flow in patients with HCM is deranged. Distally, compressive deformation of intramyocardial blood vessels during systole results in an abnormally large backward compression wave, whereas proximally, severe left ventricular outflow tract obstruction is associated with an additional deceleration wave. Perfusion abnormalities in HCM are not simply a consequence of supply/demand mismatch or remodeling of the intramyocardial blood vessels; they represent a dynamic interaction with the mechanics of myocardial ischemia that may be amenable to treatment.
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