Pathophysiology of Chronic Left Ventricular Dysfunction

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Abstract
Background Chronically dysfunctional myocardium may improve after coronary revascularization. This condition was thought to be due to a chronically reduced myocardial blood flow (MBF). Recently, however, it has been shown that in patients without previous infarction but with chronic left ventricular dysfunction, baseline MBF was normal. Methods and Results To study the pathophysiology of chronic left ventricular dysfunction in patients with previous infarction, regional MBF (milliliter per minute per gram of water-perfusable tissue) and glucose utilization (MRG; micromoles per minute per gram) during hyperinsulinemic euglycemic clamp were measured with positron emission tomography in 30 patients before bypass. At baseline, 133 myocardial segments were normal, and 107 were dysfunctional. After revascularization, 59 of 107 segments improved, while 48 of 107 were unchanged. MBF was 0.92±0.25 mL · min−1 · g−1 in normal segments, 0.87±0.31 mL · min−1 · g−1 in improved segments (P=NS versus normal), and 0.82±0.40 mL · min−1 · g−1 in unchanged segments (P<.05 versus normal). In 90% of the dysfunctional segments, MBF was >0.42 mL · min−1 · g−1, a cutoff value corresponding to the mean MBF minus 2 SD in normal segments. The MRG was 0.71±0.14 μmol · min−1 · g−1 in 9 age-matched normal subjects, 0.45±0.19 μmol · min−1 · g−1 (P<.01) in normal segments, 0.44±0.14 μmol · min−1 · g−1 in improved segments (P=NS versus normal), and 0.34±0.17 μmol · min−1 · g−1 in unchanged segments (P<.01 versus normal and improved). Conclusions The results suggest that resting MBF measured with 15O-labeled water in chronically dysfunctional segments is not reduced and that the myocardium of these patients is less sensitive to insulin than that of normal subjects.