Abstract 723: Reduced [123I]metaiodobenzylguanidine Uptake Predicts Impaired Adrenergic Myocardial Functional Reserve in Asymptomatic or Mildly Symptomatic Patients with Idiopathic Dilated Cardiomyopathy
Catecholamine sensitivity is reduced in failing hearts as a result of myocardial abnormalities in the β-adrenergic receptor (β-AR) signaling pathway. We have now evaluated the hypothesis that [123I]metaiodobenzylguanidine (MIBG) scintigraphy might predict adrenergic myocardial functional reserve in asymptomatic or mildly symptomatic DCM patients. The heart-to-mediastinum (H/M) uptake ratio in the delayed image and the washout rate of [123I]MIBG, and the maximal first derivative of left ventricular pressure with respect to time (LV dP/dtmax) and the pressure half-time (T1/2) during infusion of dobutamine (15 μg kg−1 min−1) were determined in 40 asymptomatic or mildly symptomatic patients with DCM. The abundance of mRNAs for contractile regulatory protein genes related to the β-AR signaling pathway in endomyocardial biopsy specimens was also quantified by reverse transcription and real-time polymerase chain reaction analysis. The delayed H/M ratio was directly correlated, and the washout rate was inversely correlated with each of the percentage increase in LV dP/dtmax, the percentage increase in heart rate and the percentage shortening in T1/2 during dobutamine infusion (see Table⇓). The delayed H/M ratio was also significantly correlated with the abundance of mRNAs for β1-AR and phospholamban. [123I]MIBG uptake was related to impaired adrenergic myocardial inotropic, chronotropic and lusitropic reserve associated with altered expression of β1-AR and phospholamban genes. Myocardial [123I]MIBG scintigraphy thus provides a noninvasive method for evaluation of adrenergic myocardial functional reserve in asymptomatic or mildly symptomatic patients with DCM.