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Flow Reserve From PET MPI and Benefit From Early Revascularization
Study Questions:
The prognostic value of stress positron emission tomography (PET) myocardial perfusion imaging (MPI) is well established. Can relative perfusion and quantitative myocardial flow reserve (MFR) be used to select patients who have the greatest benefit from revascularization?
Methods:
The authors conducted a retrospective single health system cohort study of 12,594 patients who were referred for rest/stress PET MPI and evaluated whether PET MPI imaging parameters of relative perfusion defects and MFR modified the effect of early revascularization on all-cause mortality. Interaction terms for MFR and % ischemic myocardium with early revascularization (either percutaneous or surgical) were used to quantify the relative difference in prognosis with and without early revascularization across a range of imaging findings. Patients with prior coronary artery bypass grafting or left ventricular ejection fraction <40% were excluded. Mortality was determined from medical records and the National Death Index.
Results:
The 12,594 included patients were followed for a median of 3.2 years. The majority of patients were female, obesity was common, and large majorities of patients had hypertension and hyperlipidemia (>70%). During follow-up, 1,699 patients died. Each unit decrease in MFR was associated with a 9% increased hazard of death (95% confidence interval [CI], 1.08-1.10; p < 0.001). Importantly, % ischemia was not related to survival once MFR was included in the model. The interaction between MFR and early revascularization was significant such that patients with MFR ≤1.8 had lower mortality with revascularization (hazard ratio [HR], 0.76; 95% CI, 0.62-0.94), while those with MFR >1.8 had worse survival with revascularization (HR, 1.39, 95% CI, 1.01-1.94). A three-way interaction test showed that % ischemia did not change the interplay between MFR and early revascularization on survival. Nonetheless, the HR for death only had CIs <1 among those patients with MFR ≤1.8 and % ischemia ≥10%.
Conclusions:
MFR on PET MPI may be helpful to identify patients who will benefit from early revascularization.
Perspective:
This paper adds to a deep literature relating quantitative measure of myocardial perfusion to clinical outcomes using PET MPI. Similar work has also been published using cardiac magnetic resonance imaging, echocardiography, and invasive measures. The novel finding is that MFR and not % ischemia was most predictive of benefit from early revascularization. This result suggests that quantitative parameters of perfusion may be more powerful than relative measures of ischemia, which has important implications for clinical management as well as for interpretation of forthcoming results from the ISCHEMIA trial. Nonetheless, some caution should be raised. First, the results are from a single health system and are retrospective. Second, the authors excluded patients with reduced contractile function and prior bypass based on concerns over accuracy. There are no data to suggest that PET MPI is not accurate in these populations, though it may have less close connection to focal coronary artery disease.
Keywords: Diagnostic Imaging, Hyperlipidemias, Hypertension, Myocardial Ischemia, Myocardial Perfusion Imaging, Myocardial Revascularization, Myocardium, Obesity, Positron-Emission Tomography
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