Investigation of parasympathetic and sympathetic cardiac innervation in diabetic neuropathy: heart rate variation versus meta-iodo-benzylguanidine measured by single photon emission computed tomography.
ABSTRACT In diabetic neuropathy disturbed autonomic cardiac innervation is associated with shortened life expectancy. Sympathetic dysfunction is likely to play a role in cases of cardiac death. The quantitative uptake of the radiopharmaceutical iodine-123-meta-iodo-benzylguanidine (MIBG) can be measured by single photon emission computed tomography (SPECT). It is an index of the functional integrity of sympathetic neurones in the heart. The respiratory heart rate variation--as assessed by a computerized device--reflects mainly parasympathetic cardiac innervation. In 25 diabetic patients and 19 healthy subjects MIBG-SPECT and heart rate variation tests were carried out. MIBG scans in all normal subjects showed homogeneous uptake of activity. In 12 out of 25 patients at least two heart rate variation tests were abnormal. MIBG-SPECT was more sensitive (abnormal in 17 out of 25). The lack of correlation between MIBG-SPECT results and spectral analysis of heart rate variation suggest that spectral analysis alone should not be regarded as an indicator of sympathetic cardiac innervation.
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ABSTRACT: Cardiovascular autonomic neuropathy (CAN) is a common complication of diabetes, which results in disabling clinical manifestations and may predispose to sudden cardiac death. Recently, direct scintigraphic assessment of cardiac sympathetic integrity has become possible with the introduction of radiolabeled analogues of norepinephrine, which are actively taken up by the sympathetic nerve terminals of the heart. This article reviews how these techniques have been utilized to improve understanding of CAN complicating diabetes. Quantitative scintigraphic assessment of cardiac sympathetic innervation heart is possible with either [123I]-metaiodobenzylguanidine (MIBG) and single photon emission computed tomography (SPECT) or [11C]-hydroxyephedrine (HED) and positron emission tomography (PET). Studies in diabetic patients have explored the sensitivity of these techniques to detect CAN, characterize the effects of glycemic control on the progression of CAN and evaluate the effects of CAN on myocardial electrophysiology, blood flow regulation and function. Deficits of left ventricular (LV) [123I]-MIBG and [11C]-HED retention have been identified in diabetic subjects without abnormalities on cardiovascular reflex testing consistent with increased sensitivity to detect CAN. Poor glycemic control results in the progression of LV tracer deficits, which can be prevented or reversed by the institution of near-euglycemia. Deficits begin distally in the LV and may extend proximally. Paradoxically, however, absolute HED retention is increased in the proximal segments of the severe CAN subjects consistent with regional "hyperinnervation." These regions also exhibit abnormal blood flow regulation. Impaired myocardial MIBG uptake correlates with altered LV diastolic filling and myocardial electrophysiological deficits and is predictive of sudden death. Scintigraphic studies have provided unique insights into the effects of diabetes on cardiac sympathetic integrity and the pathophysiological consequences of LV sympathetic dysinnervation. Future studies using complementary neurotransmitter analogues will allow different aspects of regional dysfunction to be characterized with the aim of developing therapeutic strategies to prevent or reverse CAN.Diabetes Technology & Therapeutics 02/2001; 3(1):9-22. · 1.93 Impact Factor