Electrocardiographic Effects of Glucose Ingestion

Abstract

To assess the influence of glucose ingestion on resting and exercise electrocardiograms, 35 subjects were tested after ingestion of a glucose solution and a placebo on separate days. Graded submaximal exercise tests (GXTs) were performed to 90% predicted maximal heart rate. Computer\x=req-\ processed ECGs taken at rest showed a decrease in T-wave amplitude, more ST-segment depression, increased R-wave amplitude, and increased heart rate after glucose.Minnesota code classifications of these same ECGs were more abnormal after glucose. Computer-processed exercise ECGs showed a decrease in T-wave area after glucose ingestion during and after exercise. ST-segment area showed the most variability at one minute after exercise. Three subjects had normal exercise ECGs after placebo and abnormal ECGs after glucose ingestion (ST area >7.5\g=m\v/sec). Both resting and exercise ECGs should be made fasting to avoid this significant source of variability.Longi tudi nal studies of cardiovasi cular disease frequently include both electrocardiographic and plasma glucose evaluations.1-3 Time and per¬ sonnel commitments do not always permit recording of the electrocardio¬ gram while the patient is fasting. A recent meal or ingestion of a glucose load as part of the testing routine often precedes the ECG by one or two hours. When glucose ingestion shortly precedes the ECG, the distribution of electrocardiographic findings in the population being studied may well be altered. Previous studies of the post¬ prandial resting ECG have shown changes in T-wave and R-wave am¬ plitudes, ST segment, and heart rate.415 Although Simonson et al,5·6 Dear et al15 have quantitated these changes in the resting ECG, postprandial changes in the exercise ECG have been reported in a quantitative fash¬ ion only by Klakeg et al.16 Exercise performance in this study was very mild with heart rates "immediately after exercise" of 95 to 115 beats per minute. Since the magnitude of ST-T changes depends upon the severity of exercise, comparison of the results of this one study with the results of tests using higher submaximal exer¬ cise levels is difficult.Each subject examined in the Birmingham Stroke Epidemiology Study1718 receives an orally adminis¬ tered carbohydrate load for subse¬ quent plasma glucose testing prior to his resting and exercise ECGs. Recog¬ nizing the importance of possible postprandial electrocardiographic al¬ terations, we attempted to quantitate the effects of glucose ingestion on heart rate,