Myocardial blood flow and left ventricular functional reserve in hypertrophic cardiomyopathy: a 13NH3 gated PET study

Purpose Transmural abnormalities in myocardial blood flow (MBF) are important causes of ischaemia in patients with left ventricular (LV) hypertrophy. The study aimed to test whether pixel-wise parametric mapping of 13 NH 3 MBF can reveal transmural abnormalities in patients with hypertrophic cardio-myopathy (HCM). Methods We submitted 11 HCM patients and 9 age-matched controls with physiological LV hypertrophy to rest and stress (dipyridamole) 13 NH 3 PET. We measured MBF using a compartmental model, and obtained rest and stress parametric maps. Pixel MBF values were reorganized to obtain subendocardial and subepicardial MBF of LV segments. Results MBF at rest was higher in the subendocardial than in the subepicardial layer: 0.78±0.19 vs. 0.60±0.18 mL/min/g in HCM patients; 0.92±0.24 vs. 0.75±0.24 mL/min/g in controls (both p < 0.0001). Transmural perfusion gradient (TPG=subendocardial MBF/subepicardial MBF) at rest was similar: 1.35±0.31 in HCM patients; 1.28±0.27 in controls (NS). During stress, controls maintained higher subendocardial MBF: 2.44 ± 0.54 vs. 1.96 ± 0.67 mL/min/g tissue (p < 0.0001), with a TPG of 1.33± 0.35 (NS vs. rest). In HCM patients, the difference between subendocardial and subepicardial MBF was reduced (1.46 ± 0.48 vs. 1.36 ± 0.48 mL/min/g tissue, p<0.01) and TPG decreased to 1.11± 0.34 (p<0.0001 vs. rest and vs. controls). In HCM patients 8 of 176 segments had subendocardial MBF less than −2 × SD of the mean, versus none of 144 segments in controls (p<0.01). Conclusion Pixel-wise parametric mapping of 13 NH 3 MBF enables the identification of transmural abnormalities in patients with HCM.