Cardiac autonomic dysfunction in type 2 diabetes mellitus: Insights from one minute electrocardiogram studies

Diabetes mellitus is a metabolic disorder affecting various organs of the body. In many patients with diabetes mellitus, typical symptoms associated with the disease manifest only after sufficient cumulative effect of diabetes mellitus. As a result, diabetes-related complications and associated clinical conditions may be present by the time it is clinically diagnosed. One such diabetic complication which remains subclinical is autonomic neuropathy. Diabetic neuropathy is associated with morbidity and mortality. In the light of increased mortality rate associated with diabetic autonomic neuropathy, and its possible involvement in other complications it is of utmost importance to assess cardiac autonomic function periodically for long-term treatment strategies. Among the different non-invasive techniques for assessing autonomic status, heart rate variability has emerged as a major tool in the diagnostic and monitoring armamentarium.Currently, based on the recommendations of task force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology time domain measures of heart rate variability are typically obtained from a routine 24-h ambulatory electro-cardiogram. However heart rate variability parameters derived from much lesser duration may be more appropriate for routine clinical assessment of cardiac autonomic dysfunction. This article portrays insights from one minute electrocardiogram studies on assessment of cardiac autonomic dysfunction in type 2 diabetes mellitus; wherein, heart rate response and Inspiratory: Expiratory ratio are derived from lead II electrocardiogram while deep breathing at 6 respiratory cycles per minute; rMSSD and SDNN are derived from lead II electrocardiogram while breathing spontaneously in resting supine position.Analysis of heart rate response to deep breathing at 6 respiratory cycles per minute at baseline reveals that, among the clinical characteristics of type 2 diabetes mellitus, somatic neuropathy is an independent predictor of cardiac parasympathetic dysfunction. Age and female gender are the other predictors of reduced heart rate response to deep breathing in type 2 diabetes mellitus.Monitoring cardiac autonomic function over one year period reveals that cardiac autonomic function deteriorates with time and essentially in presence of somatic neuropathy and cardiovascular disease. rMSSD an indicator of parasympathetic activity detects deterioration in cardiac autonomic dysfunction coexisting with somatic neuropathy and cardiovascular disease. But Expiratory: Inspiratory ratio another indicator of parasympathetic function is a suitable marker in monitoring cardiac autonomic dysfunction coexisting with somatic neuropathy. Similarly, SDNN an indicator of parasympathetic and sympathetic selectively quantifies cardiac autonomic dysfunction coexisting mainly with cardiovascular disease. Thus these findings suggest the possible utility of time domain measures of heart rate variability derived from one minute electrocardiogram in routine clinical assessment of cardiac parasympathetic dysfunction in type 2 diabetes mellitus.