The Effect of Fasting on QT Interval

Experimental hypoglycaemia and spontaneous clinical episodes of hypoglycaemia lead to the lengthening of the heart rate corrected QT interval or QTc. This is associated with elevated risk of sudden death. Objective: To find out the effect of fasting blood glucose levels on QT interval and the corrected QT interval (QTc). Materials and Methods: Fasting and post prandial blood glucose levels and ECG of healthy young adults were studied and QT interval, RR interval and QTc were determined. Results: The fasting QTc came out to be 0.408+-0.020 as compared to the post prandial value of 0.380+-0.0 19. The student's t test showed a highly significant value (p<O.OOOI).Conclusion: There is significant prolongation of QT interval and QTc during fasting bu within normal physiological limits.

bronchial asthma, systemic infection, arrhythmias or abnormal electrocardiogram or those who had taken any kind of drugs within 2 weeks before study were excluded from the study.Materials: Used were glucometer, ECG machine, weight machine, vernier calipers etc. Study protocol: Written informed consent was taken from ea h subject.Five students were examined each day.They were advised to come to the study ite after an overnight fast of I hours.They took light supper at to 9 pm.Plain water \ allowed till 12 midnight.Fasting Blood Glucose Level -recorded the following morning between 10-11 am at Ph_ iology Lab King Edward edical niversity, followed by a 12 lead ECG after which the participants had breakfast whi h onsisted of 2 fried eggs, 2 pieces of bread, butter and a g of whole milk.Subsequently post prandial ECG and Blood Glu ose Levels were recorded.The ECG recording of every ubje t was studied for QT interval, RR interval and QT wa determined.
Height and weight without shoes and with light clothing was determined and body mass index or Quetelet's index (\\I eight in kg/ height in meter square} was calculated for each subject.Blood pressure was recorded with mercury sphygmomanometer.Measuremenr of QT interval: The QT interval was manually measured by using hand-held calipers from the beginning of the QRS complex to the end of T wave.The end of T wave was defined as the intersection between a tangent to the terminal slope of the T wave and the PR baseline.Only monophasic well defined T waves were accepted for measurement.If a U wave was present, then the tangent was drawn on the terminal slope of T wave and its end was determined as point of intersection of this line with the isoelectric base.The QT interval and preceding RR interval were measured in three consecutive cycles.All ECG's were analyzed by single observer.The physiological determinants of QT interval include age 27 and sex 28 ,29.Our exclusion criterion was designed to rule out all these causes of QT prolongation.The study was performed on a specified age group of 18-22 years old individuals including both females and males.
In a normal person, with heart rate of 75 beats/min, it varies from 0.35-0.40seconds.In our study mean QT interval was 0.337±0.022,The QT interval increased during fasting to an average of 0.366.Although within physiologicallirnits, this increase of QT interval in fasting is an important finding, and whether this increase of QT interval is harmful or even causes ventricular arrhythmias in cardiac patients, should be studied later.When we corrected the QT Interval for heart rate, the interval was still prolonged but less as compared to QT.
After 12 to 15 hours offasting, hepatic glycogen stores are greatly depleted and continuing enhancement of gluconeogenesis fills the void.
uch of this pattern of adaptation is mediated by hormonal modification, particularly by decreasing insulin production and by increasing glucagons production.Hypoglycemia exerts haemodynamic effects through stimulation of the autonomic nervous system as well as through systemic release. of catecholamines'".
Prolongation of QTc interval during fasting support the idea that ventricular repolarization may be changed during fasting.It has been reported that increase in QTc interval may be due to acidosis and decrease of bicarbonate' ion or hypoglycemia, which may all cause a decrease in outward current during repolarization period.However confirmation of this hypothesis needs further investigations-In the presence of hypokalemia and raised serum catechola ines, often present during h oglycaernia, cardiac repolarization could be prolonged enough 0 induce cardiac arrhythmias".It is well recognised that pon ssium depletion leads to increased QTc interval length and to arrhythmogenesis with increased likelihood of development of ventricular dysrhythmia such as torsade de pointes 32 ,33.Rk-intervals were also longer during fasting. in contrast to conti 91 electrocardiograms but this was not statistically significant.This finding shows that relative bradycardia may occur during fasting.
_.' So, fasting prolongs QT Interval and-,QTc-but within the physiological limits.This is evident from our study when dealing with healthy individuals.Diabetic patients who suffer from hypoglycemic.episodes can show exaggeration of this phen menon th t is prolongation ofthe QT Interval and QTc beyond the physiological limits .andA'.. _ ALS VOL. 13 NO.) Figure.
J,\ -MAR 2007 117 I end up with fatal arrhythmias.J.