Silent myocardial ischemia: role of subclinical neuropathy in patients with and without diabetes.
OBJECTIVE
Silent myocardial ischemia is common in patients with diabetes. This study was designed to assess the role of subclinical autonomic impairment in diabetic patients with silent ischemia.


BACKGROUND
Studies have suggested that silent ischemia is more common in diabetic patients with microvascular complications, but this has not been a consistent finding.


METHODS
Twenty-two diabetic and 30 nondiabetic patients with proved coronary artery disease and a history of angina and ischemia on treadmill stress testing underwent clinical tests of autonomic function and measurement of 24-h heart rate variability. Diabetic patients with a history of microvascular complications were excluded.


RESULTS
Although all 52 patients manifested ischemia during treadmill testing, only 36 patients experienced angina (angina group), whereas 16 did not (silent ischemia group). Diabetic and nondiabetic patients were similar in age (59 +/- 1 vs. 61 +/- 2 years, p = 0.56) and extent of coronary artery disease. However, clinical tests showed reduced parasympathetic function in the diabetic patients (Valsalva ratio 1.38 +/- 0.07 vs. 1.60 +/- 0.06; p = 0.007). Patients in the silent ischemia group were more often diabetic (33% vs. 63%, p = 0.05) and had prolonged time to ischemia on treadmill testing (200 +/- 20 vs. 271 +/- 20 s, p = 0.03). In addition, autonomic function was impaired in the silent group (supine/standing heart rate ratio 1.15 +/- 0.02 vs. 1.05 +/- 0.02, p = 0.002). Subgroup analysis showed that abnormalities of autonomic function were confined to the diabetic patients in the silent group.


CONCLUSIONS
Despite the absence of overt microvascular complications, diabetic patients with silent exertional ischemia have evidence of significant autonomic impairment compared with findings in symptomatic patients. This difference is not seen in nondiabetic patients and indicates that subclinical neuropathy is an important cause of silent ischemia in patients with diabetes.
Marchant
B
B
Department of Cardiology, London Chest Hospital, United Kingdom.
Umachandran
V
V
Stevenson
R
R
Kopelman
P G
PG
Timmis
A D
AD
D000328:Adult; D000368:Aged; D000787:Angina Pectoris / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D001342:Autonomic Nervous System Diseases / Q000150:complications*; D016022:Case-Control Studies; D017023:Coronary Angiography; D003327:Coronary Disease / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D003929:Diabetic Neuropathies / Q000150:complications*; D015716:Electrocardiography, Ambulatory; D005080:Exercise Test; D005260:Female; D015637:Gated Blood-Pool Imaging; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D010275:Parasympathetic Nervous System; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013318:Stroke Volume; D016683:Supine Position; D013997:Time Factors; D014636:Valsalva Maneuver