Blood glucose variability impacts heart rate dynamics in older type 2 diabetic and coronary heart disease patients

Cardiac autonomic neuropathy correlates intimately with cardiovascular complications and unexpected death. It is a typical clinical abnormality seen in coronary artery disease-affected individuals with concurrent type 2 diabetes mellitus (T2DM). Moreover, blood glucose (BG) variability has been clinically shown to induce cardiovascular events and sudden death.

To investigate how BG variability impacts heart rate (HR) dynamics in older adults with T2DM + coronary heart disease (CHD) and to evaluate the ability of functional myocardial ischemia to predict outcomes in this cohort.

We enrolled 143 older T2DM + CHD patients admitted to the First Affiliated Hospital, Hengyang Medical School, University of South China over a 3.5-year period (January 2018 to July 2021). Using a standard deviation of BG cutoff of 1.4 mmol/L, subjects were stratified into abnormal (n = 75) and normal (n = 68) fluctuation groups. All patients underwent 72-hour dynamic BG monitoring to detect BG fluctuation parameters. The time domain index of HR variability was measured by dynamic electrocardiogram. To determine how well glucose fluctuation measures predicted functional myocardial ischemia, the area under the receiver operating characteristic curve (AUC) was calculated.

The abnormal fluctuation group showed greater levels of mean amplitude of glycemic excursions (MAGE), mean of daily differences (MODD), largest amplitude of glycemic excursions (LAGE), and mean postprandial glucose excursions (MPPGE) relative to the normal group (P < 0.05), along with lower levels of standard deviation of normal-to-normal (NN) interval (SDNN), standard deviation of the average NN interval (SDANN), standard deviation of NN intervals over every 5-minute period (SDNNindex), root mean square of successive differences (rMSSD), and percentage of NN intervals differing by > 50 ms (pNN50; P < 0.05). Pearson correlation analysis showed that MAGE, MODD, LAGE, and MPPGE were negatively correlated with SDNN, SDANN, SDNNindex, rMSSD, and pNN50 in older patients with T2DM complicated by CHD (P < 0.05). The AUC of MAGE combined with MPPGE in predicting the occurrence of functional myocardial ischemia was 0.912, which was significantly higher than 0.694 of SDNN (P < 0.05).

A negative correlation was found between BG variability and HR dynamics in older CHD + T2DM patients, and MAGE combined with MPPGE demonstrated better efficacy in predicting functional myocardial ischemia, which deserves clinical attention.