Matching of myocardial oxygen consumption to mechanical load in human left ventricular hypertrophy and dysfunction

The coupling of myocardial oxygen consumption (MVO2) with its determinants in left ventricular hypertrophy in human beings is poorly understood. Therefore, thermodilution-derived coronary blood flow, MVO2 and left ventricular wall stress, obtained from simultaneous left ventricular M-mode echogram and pressure, were compared in 32 patients with various degrees of left ventricular hypertrophy. Patients were studied at rest and after mechanical load alteration with nitroglycerin or phenylephrine. Decreases in MVO2 (-5.7 +/- 0.8 ml/min; p less than 0.001) and the time integral of meridional ejection stress or shortening load (-1,297 +/- 152 X 10(3) dynes X s/cm2; p less than 0.001) were observed after nitroglycerin administration while increases in MVO2 (+5.5 +/- 0.7 ml/min; p less than 0.001) and shortening load (+1,412 +/- 137 X 10(3) dynes X s/cm2; p less than 0.001) were noted after phenylephrine. An index relating the change in MVO2 to the corresponding change in shortening load (SL), % delta MVO2/% delta SL, was significantly different in patients without (Group 1) and with (Group 2) clinical left ventricular failure. Left ventricular mass was similar in both groups. The mean % delta MVO2/% delta SL with phenylephrine in Group 1 (79.6 +/- 9.6) was greater than the index for Group 2 (35.5 +/- 6.1; p less than 0.005). With nitroglycerin, Group 2 patients exhibited a greater reduction in % delta MVO2/% delta SL (110.5 +/- 17.8) than Group 1 (54.0 +/- 9.4; p less than 0.01). In conclusion, in patients with left ventricular hypertrophy and dysfunction there appears to be a state of diminished coronary flow response to load augmentation. However, load reduction in patients with clinical left ventricular failure results in a more balanced relation between oxygen uptake and ejection stress.