Myocardial m-[¹²³I]Iodobenzylguanidine Scintigraphy for the Assessment of Adrenergic Cardiac Innervation in Patients With IDDM: Comparison With Cardiovascular Reflex Tests and Relationship to Left Ventricular Function

Cardiac imaging using m-[¹²³I]iodobenzylguanidine (mIBG) reflects sympathetic myocardial innervation. In patients with insulin-dependent diabetes mellitus (IDDM), the following were studied: 1) the prevalence of derangements of cardiac autonomic innervation as detected by mIBG scintigraphy in comparison with cardiovascular reflex tests and 2) the relationship between adrenergic cardiac innervation and left ventricular (LV) function. Twenty-four patients with IDDM without overt heart disease were studied after silent coronary artery disease was excluded by ²⁰¹Tl scintigraphy. Cardiac innervation was evaluated by both mIBG scintigraphy (tomographic imaging) and cardiovascular reflex tests. Systolic (ejection fraction [EF] percentage) and diastolic (peak filling rate [PFR] defined as end-diastolic volumes per second [EDV/s]) LV function were determined by equilibrium radionuclide angiography at rest and during bicycle exercise. mIBG scintigraphy was also performed in 10 control subjects. All control subjects exhibited a normal myocardial mIBG distribution. Among diabetic patients, only six had normal mIBG scans (group 1), whereas 18 had evidence of regional adrenergic denervation (group 2). Reflex tests suggested cardiac autonomic neuropathy in only seven of these patients (P < 0.01 vs. mIBG). All patients had a normal EF at rest. However, group 2 showed an impaired response to exercise as indicated by a smaller increase in EF (5 ± 6 vs. 13 ± 5%, P < 0.05) and a lower PFR (5.9 ± 0.8 vs. 7.3 ± 1.2 EDV/s, P < 0.01). Myocardial mIBG scintigraphy reveals that in patients with IDDM, sympathetic myocardial dysinnervation is much more common than previously thought. Furthermore, subclinical LV dysfunction is related to derangements of adrenergic cardiac innervation.