Abstract 11279: A Rapid Method to Evaluate Cardiac Repolarization Changes: The Effect of Two Coffee Strengths on the QT interval

Abstract

Background: Coffee is a widely used beverage, consumed for its stimulant effect, which is attributed to caffeine. Controversy exists about the acute and chronic cardiovascular effects of coffee in man including potential arrhythmogenicity. Surprisingly, very few studies with conflicting results have evaluated the effect of coffee or caffeine on ventricular repolarization. This is especially important in that prolongation in ventricular repolarization may lead to ventricular arrhythmias. The primary objective of this study was to assess the effect of coffee on ventricular repolarization as measured by the QT/QTc interval obtained from the body surface ECG. Methods: Fifty four healthy volunteers (34 males, 20 females, age: 23±5 years) received 1 cup coffee (caffeine: 120 mg) and 11 volunteers received 2 cups. Blood pressure (BP) and heart rate (HR) were measured prior to coffee and every hour thereafter for 5 hours. A 12-lead digital Holter was recorder continuously. The Holter analysis system automatically generates a representative median QRST complex for each 1 minute segment of the recordings and measures RR and QT intervals. The position of cursors indicating the beginning of the QRS complex and the end of the T wave were visually evaluated and their positions adjusted (as needed). The system has been validated for QT/QTc analysis. RR, QT and QTc intervals were tabulated every 30 minutes. The QTc intervals were calculated by the Fridericia formula. Results: Following coffee, maximum changes were noted at 1.5 hr in RR which increased from 802±102 to 873±126 ms (p=0.001), and QT increased from 359±26 to 367±27 ms. The QTc shortened from 387±21 to 381±23 ms at 30 minutes (p=0.001) with no significant changes noted at the other time points. The HR decreased from 73±9 to 69±11 bpm at 1 hr. (p=0.018). There were no significant changes in BP. The effects of 1 or 2 cups coffee did not differ on QTc (p=0.663), HR (p=0.161), diastolic (p=0.250) or systolic BP (p=0.168). Caffeine users and caffeine naïve subjects did not differ in QTc effect (p=0.971). Females had longer QTc at each time point than males (p=0.037) but neither had QTc prolongation following coffee. Conclusion: Neither 1 nor 2 cups of coffee prolonged ventricular repolarization as measured by the QTc interval.