Study objective: Doppler-derived myocardial performance index (MPI), a measure of combined systolic and diastolic myocardial performance, was assessed at rest and after low-dose dobutamine administration in patients with idiopathic or ischemic dilated cardiomyopathy. MPI also was correlated with other conventional echocardiographic indexes of left ventricular (LV) function, and its ability to assess cardiopulmonary exercise capacity in those patients was investigated.
Settings: A tertiary-care, university heart failure clinic.
Patients: Forty-two consecutive patients (27 men; mean [± SD] age, 57 ± 10 years) with heart failure (New York Heart Association [NYHA] class, II to IV) who had received echocardiographic diagnoses of dilated cardiomyopathy. Coronary angiography distinguished the cause of dilated cardiomyopathy.
Interventions: Low-dose IV dobutamine was infused after patients underwent a baseline echocardiographic study. All patients also underwent a cardiopulmonary exercise test using a modified Naughton protocol.
Results: Advanced NYHA class and restrictive LV filling pattern were associated with higher index values. A negative correlation was found between MPI and LV stroke volume, cardiac output, early filling/late filling velocity ratio, and late LV filling velocity, as well as oxygen uptake at peak exercise (r = −0.550; p < 0.001) and at the anaerobic threshold (r = −0.490; p = 0.002). Dobutamine administration produced an improvement in MPI, reducing its value and decreasing the isovolumic relaxation and contraction times. Stepwise regression analysis revealed that the rest index and the late LV filling velocity were the only independent predictors of cardiopulmonary exercise capacity.
Conclusion: MPI correlates inversely with LV performance, reflects disease severity, and is a useful complimentary variable in the assessment of cardiopulmonary exercise performance in patients with heart failure.