Dobutamine stress testing as a diagnostic tool for evaluation of myocardial contractile reserve in asymptomatic or mildly symptomatic patients with dilated cardiomyopathy.

Objectives We performed dobutamine stress testing for evaluation of myocardial contractile reserve in asymptomatic or mildly symptomatic patients with dilated cardiomyopathy (DCM). Background Catecholamine sensitivity is reduced in failing hearts as a result of myocardial abnormalities in the beta-adrenergic receptor signaling pathway. However, little is known about adrenergic myocardial contractile reserve in asymptomatic or mildly symptomatic patients with DCM. Methods The maximal first derivative of left ventricular pressure (LV dP/dt max ) was determined during infusion of dobutamine (10 μg kg −1 min −1 ) in 46 asymptomatic or mildly symptomatic (New York Heart Association functional class I or II) patients with DCM. The expression of messenger ribonucleic acid (mRNA) for contractile regulatory proteins in endomyocardial biopsy specimens was quantified by reverse transcription and real-time polymerase chain reaction analysis. Plasma norepinephrine levels were measured in all patients and [ 123 I]metaiodobenzylguanidine (MIBG) scintigraphy performed. Results Patients were classified into 3 groups based on the percentage increase in LV dP/dt max induced by dobutamine (ΔLV dP/dt max ) and on LV ejection fraction (LVEF) at baseline: group I (n = 18): ΔLV dP/dt max >100% and LVEF >25%; group IIa (n = 17): ΔLV dP/dt max ≤100% and LVEF > 25%; and group IIb (n = 11): ΔLV dP/dt max ≤100% and LVEF ≤25%. The amounts of beta 1 -adrenergic receptor, sarcoplasmic reticulum Ca 2+ -adenosine triphosphatase, and phospholamban mRNA were significantly smaller in groups IIa and IIb than in group I. The plasma norepinephrine level was increased and the delayed heart/mediastinum count ratio in MIBG scintigraphy was decreased in both groups IIa and IIb. Conclusions Dobutamine stress testing is a useful diagnostic tool for identifying reduced adrenergic myocardial contractile reserve related to altered myocardial expression of beta 1 -adrenergic receptor, sarcoplasmic reticulum Ca 2+ -adenosine triphosphatase, and phospholamban genes even in asymptomatic or mildly symptomatic patients with DCM.