Cardiac PET in aortic stenosis: Potential role in risk refinement?

Abstract

An 80-year-old gentleman, with a 60 pack-year smoking history, hyperlipidemia and moderate aortic stenosis (transthoracic echocardiogram (TTE) 2 years before the current presentation: valve area 1.38 cm, index valve area 0.61 cm/m, mean gradient 19 mmHg, dimensionless index 0.33, and cardiac output 6.3 l/min) was seen in the clinic for evaluation of shortness of breath NYHA II with generalized weakness since two months. He did not report syncope, chest pain, orthopnea, or paroxysmal nocturnal dyspnea. He had mild chronic bilateral lower limb edema due to venous insufficiency. He was on aspirin and statin for primary prevention andmetoprolol succinate for controlled hypertension. A 12-lead electrocardiogram showed regular sinus rhythm with evidence of left atrial enlargement and borderline left ventricular (LV) hypertrophy. TTE at the current visit showed preserved LV ejection fraction and aortic stenosis (AS) with an aortic valve area of 1.32 cm, index valve area 0.59 cm/m, peak/mean gradient 57/31 mmHg, peak velocity 3.8 m/s, dimensionless index of 0.33, and cardiac output 7 liters/min. He underwent a 3D dynamic PET imaging with Rubidium82 (30.2 mCi at stress and 30.0 mCi at rest) and regadenoson as a stress agent for his symptoms to evaluate for coronary artery disease (CAD). Blood pressure and heart rate at rest were 129/70 mmHg and 72/min, respectively. There was no electrocardiographic evidence of ischemia. Immediate post-stress blood pressure and heart rate were 112/54 mmHg and 76/ min, respectively. Perfusion images (Figure 1) showed no evidence of ischemic or fixed perfusion defects with mild visual transient ischemic dilation. A gated study (Figure 2) showed normal LV ejection fraction at rest and stress. Flow analysis of dynamic data to derive myocardial blood flow (MBF) and myocardial flow reserve (MFR) using single compartmental model was performed with manual motion correction as needed. Rate-pressure product correction was not done. At rest, there was normal MBF in all coronary artery territories. At stress, there was a mild reduction in peak MBF in the right coronary artery (RCA) and the left circumflex artery (LCx) distribution with a moderate reduction in peak MBF in the left anterior descending (LAD) artery territory. The regional MFR was impaired in all coronary territories and the global MFR was abnormal at\\ 2 (Figure 3). Due to blunted peak flows, mild visual TID and abnormal MFR, a coronary angiogram was performed and showed moderate (60%) RCA stenosis with an instantaneous wave-free ratio of 0.94 suggesting no hemodynamic significance, moderate (50%) LCx stenosis, and only mild (1–25%) LAD stenosis (Figure 4). Peak-to-peak AV gradient during invasive angiography was 46 mmHg with a calculated valve area of 0.99 cm, and cardiac output of 7.4 liters/min by Fick principle. Overall indices suggested severe AS. The patient was scheduled for transcatheter AV replacement.