Assessment of impact of left ventricular flow state on myocardial blood flow using positron emission tomography and echocardiography

Abstract Background The relationship between left ventricular (LV) mass and myocardial blood flow (MBF) has been recognized as an important physiological measure of myocardial perfusion to match global metabolic demand. However, there is little information on the association between LV flow state and MBF. Purpose To investigate impact of LV flow state on MBF. Methods The study included 104 patients undergoing cardiac positron emission tomography (PET) and echocardiography for chest pain and/or dyspnoea. CT attenuation corrected rest/regadenoson stress 13N-ammonia myocardial perfusion imaging was acquired with a PET CT camera. All images were acquired in 3-D list mode. Sixteen dynamic frames were reconstructed and analyzed with QPET software to obtain rest quantitative MBF measurements adjusted for rate-pressure product in ml/min/g, with a myocardial flow reserve (MFR) derived as the ratio of stress MBF/resting MBF. All patients had no ischaemia or infarction with LV ejection fraction ≥55%. Echocardiography was performed within 6 months of PET in clinically stable conditions allowing for. SV was measured by Doppler echocardiography using the continuity equation and was indexed by body surface area (SVi). The patients were divided to normal flow group (NFS: SVi > 35 ml/m2) and low flow group (LFS: SVi≤35 ml/m2). Results The mean SVi was 40 ml/m2 for NFS and 29 ml/m2 for LFS (p<0.001). LFS group was younger (57 ± 11 vs. 67 ± 11 years, p<0.001) with higher body mass index (43±8 vs. 37±8 kg/m2, p<0.001) and lower resting MBF (0.84±0.22 vs. 1.02±0.34 ml/min/g, p<0.01) than NFS groups. There were no significant differences of hypertension (81% vs. 82%, p> 0.05), LV mass index (82±21 vs. 88±82 g/m2, p>0.05), LVEF (63% vs. 65%, p>0.05) between LFS and NFS groups. SVi was positively associated with MBF as a whole group (r= 0.38, p<0.01). However, this significant association was only observed in NFS group (r=0.62, p <0.001), but not in LFS group (r=0.048, p= 0.46, Figure). Conclusion LFS expressed low MBF and the dissociation between SVi and MBF in comparison with NFS group suggesting potential alterations in relationships between myocardial work (SV) and oxygen consumption (MBF) in LFS. Further studies are warranted to investigate the pathophysiology behind the findings and to correlate with a long-term clinical outcome.