A Rapid Method to Evaluate Cardiac Repolarization Changes: The Effect of Two Coffee Strengths on the QT Interval
1American Institute of Therapeutics, Lake Bluff, Ill., USA.
Objectives:
To assess the effect of coffee on ventricular repolarization as measured by an electrocardiogram.
Methods:
Fifty-four healthy volunteers (34 males and 20 females, age 23 ± 5 years) received 1 cup of coffee (caffeine content 120 mg) and 11 participants received 2 cups. Blood pressure and heart rate were measured prior to coffee and every hour thereafter for 5 h. A 12-lead digital Holter recorded continuously, and RR, QT, and QTc intervals were obtained every 30 min.
Results:
Following coffee, RR increased from 802 ± 102 to 873 ± 126 ms (p = 0.001), QT increased from 359 ± 26 to 367 ± 27 ms at 1.5 h (p = 0.047), and QTc decreased from 387 ± 21 to 381 ± 23 ms at 30 min (p = 0.001), with no changes noted at other time points. Caffeine users and caffeine-naive subjects did not differ in QTc effects (p = 0.971). Females had longer QTc at each time point than males (p = 0.037), but neither had QTc prolongation following coffee. The heart rate decreased from 73 ± 9 to 69 ± 11 bpm at 1 h (p = 0.018), and no significant changes in blood pressure were noted. The effects of 1 or 2 cups of coffee did not differ in terms of QTc (p = 0.663), heart rate (p = 0.161), diastolic (p = 0.250), or systolic blood pressure (p = 0.168).
Conclusion:
Neither 1 nor 2 cups of coffee increased ventricular repolarization.
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