Association of PET-measured myocardial flow reserve with echocardiography-estimated pulmonary artery systolic pressure in patients with hypertrophic cardiomyopathy

Abstract

Background: Pulmonary hypertension (PH) is a known complication of HCM and is a strong predictor of mortality. We aim to investigate the relationship between microvascular dysfunction measured by quantitative PET and PH in HCM patients.

Methods: Eighty-nine symptomatic HCM patients were included in the study. Each patient underwent two 20-min 13N-NH3 dynamic PET scans for rest and stress conditions, respectively. A 2-tissue irreversible compartmental model was used to fit the segments time activity curves for estimating segmental and global myocardial blood flow (MBF) and myocardial flow reserve (MFR). Echocardiographic derived PASP was utilized to estimate PH.

Results: Patients were categorized into two groups across PASP: PH (PASP > 36 mmHg) and no-PH (PASP ≤ 36 mmHg). patients with PH had larger left atrium, ratio of higher inflow early diastole (E) and atrial contraction (A) waves, E/A, and ratio of inflow and peak early diastolic waves, E/e', significantly reduced global stress MBF (1.85 ± 0.52 vs. 2.13 ± 0.56 ml/min/g; p = 0.024) and MFR (2.21 ± 0.57 vs. 2.62 ± 0.75; p = 0.005), while the MBFs at rest between the two groups were similar. There were significant negative correlations between global stress MBF/MFR and PASP (stress MBF: r = -0.23, p = 0.03; MFR: r = -0.32, p = 0.002); for regional MBF and MFR measurements, the highest linear correlation coefficients were observed in the septal wall (stress MBF: r = -0.27, p = 0.01; MFR: r = -0.31, p = 0.003). Global MFR was identified to be independent predictor for PH in multivariate regression analysis.

Conclusion: Echocardiography-derived PASP is negatively correlated with global MFR measured by 13N-NH3 dynamic PET. Global MFR is suggested to be an index of PH in HCM patients.

Fig 1. Representative cases of HCM with or without PH.

(A1, B1): patient A is a 56-year-old female with normal PASP showing no evidence of vasodilator stress-induced myocardial ischemia; patient B is a 37-year-old female with elevated PASP revealing global myocardial ischemia but most severe in mid to apical regions of lateral and anterior walls; Lines from left to right: short axial slice; vertical axial slice; horizontal axial slice; (A2, B2): Time-activity curves at stress and rest. Dashed line: arterial blood; Hollow dots: myocardial time-activity curve of apical-lateral segment measured by PET; Solid line: myocardial time-activity curve predicted by the model.

Fig 2. Comparison of global and regional MBF/ MFR between HCM patients with and without PH.

A: stress MBF; B: rest MBF; C: MFR. *p<0.05, **p<0.01 for comparison between PH versus no PH.

Fig 3. Correlation between PASP and PET parameters in the total HCM cohort.

(A1,A2):correlation between PASP and global/regional stress MBF; (B1,B2): correlation between PASP and global/regional rest MBF; (C1,C2): correlation between PASP and global/regional MFR.