Estimation of Flow Reserve Capacity of Penetrating Intramyocardial Coronary Arteries in Apical Hypertrophic Cardiomyopathy: Study Using Transthoracic Doppler Echocardiography

BACKGROUND AND OBJECTIVES: The characterization of penetrating intramyocardial coronary artery (PICA) flow in diseased myocardium may offer insight into the spectrum of coronary physiology. However, the Coronary flow reserve (CFR) of PICA in apical hypertrophic cardiomyopathy (AH) has not yet been studied. This study tested the feasibility of CFR measurements of PICA by using high-frequency transthoracic Doppler echocardiography (TTE) and evaluated the hemodynamic and morphologic differences of PICA between patients with AH and patients without hypertrophy.

SUBJECTS AND METHODS: In 65 subjects with normal coronary angiograms [mean age 56±10 yrs;M:F=33:32;30 normotensive subjects without hypertrophy (Control group);24 hypertension subjects without hypertrophy (HTN group);11 subjects with apical hypertrophic cardiomyopathy (AH group)], we examined the myocardium just beneath the apical impulse window at a depth of 3 to 5 cm using TTE (7-MHz broadband transducer). After obtaining linear color signals using a special preset coronary program with a low Nyquist limit (12 to 20 cm), the width, peak (PDV) and mean (MDV) diastolic pulsed Doppler velocities, and diastolic velocity time integrals (VTI) were measured. PICA-CFR was calculated as the ratio of hyperemic PDV after the intravenous infusion of adenosine (140 microgram/kg/min) to baseline PDV. The PICA-width ratio was calculated as the ratio of hyperemic to baseline width of color Doppler signals of PICA.

RESULTS: PICA-CFR was successfully measured in 59 (90.8%) of the 65 subjects. Baseline PDV of PICA was 39.6±21.0 cm/s in the AH group, 18.5±5.8 cm/s in the HTN group, and 17.5±6.8 cm/s in the control group (p<0.005 versus HTN and Control). The baseline width of PICA was 1.48±0.49 mm in the AH group, 1.15±0.32 mm in the HTN group, and 1.12±0.33 mm in the control group (p=0.039 versus HTN group and control group), respectively, and the PICA-CFR was 1.65±0.49 in the AH group, 2.50±0.77 in the HTN group, and 2.42±0.73 in the control group (p<0.005 versus HTN and Control), respectively. Lastly, the PICA-width ratio was 1.45±0.42 in the AH group, 2.14±0.72 in the HTN group, and 1.81±0.55 in the control group (p=0.005 versus HTN and Control). PICA-CFR was closely related to the width-ratio of PICA (r=0.448, p=0.002) and to the epicardial-CFR ratio (r=0.753, p=0.003).

CONCLUSION: Measurement of PICA-CFR is feasible in a high percentage of subjects by using high-frequency TTE. PICA in AH has higher resting velocity, wider diameter and more impaired CFR than that in control. The characterization of PICA flow may offer insight into the spectrum of coronary physiology.