Dipyridamole myocardial SPECT with low heart rate response indicates cardiac autonomic dysfunction in patients with diabetes

Background. Because dipyridamole is used to assess heart rate (HR) variabil ity, we investigated whether a low HR response during dipyridamole single p hoton emission computed tomography (SPECT) in patients with diabetes indica tes the presence of cardiac autonomic neuropathy (CAN), Methods and Results. Subjects were 61 non-insulin-dependent diabetes patien ts without perfusion defects, myocardial infarction, or arrhythmia who unde rwent thallium 201 SPECT imaging, The control group comprised 28 subjects w ithout diabetes. HR was measured during infusion of dipyridamole at a rate of 0.14 mg/kg/min, and peak-baseline ratios of 1.20 or less were defined as low CAN severity was classified by standard autonomic function tests as se vere (n = 22), mild (n = 19), or none (n = 20), IIR ratios were significant ly attenuated in patients with diabetes compared with those in control subj ects (1.22 +/- 0.12 vs 1.32 +/- 0,12, P < .001). Among the patients with di abetes, HR ratios decreased as CAN severity increased from none (1.32 <plus /minus> 0.10) to mild (1.23 +/- 0,12, P < .05) to severe (1.13 <plus/minus> 0,08, P < ,005), There was good correlation between HR ratio and R-R inter val ratio to deep breathing and to Valsalva, and patients with low HR ratio s showed an attenuated response to both tests tall P < ,001), The sensitivi ty and specificity of HR ratios in the detection of CAN were 77% and 74% fo r severe CAN and 63% and 90% for mild-to-severe CAN, respectively. Conclusions, In patients with diabetes who have normal dipyridamole SPECT r esults, an attenuated HR response observed during stress indicates a high l ikelihood of CAN. Further work that assesses these results in diabetes pati ents with coronary artery disease is warranted.