case_images: PMC3971859_01
case_images: Baseline electrocardiogram demonstrating normal baseline conduction.
case_images: CRIVAM2014-204805.001.jpg
case_images: PMC3971859_01_CRIVAM2014-204805.001.jpg
case_images: fig1
case_images: She had a normal physical exam and her only medication was an oral contraceptive. 12-lead electrocardiogram was normal with the following intervals: PR interval was 154 millisecond (msec), QRS was narrow at 82 msec, and QT interval was normal at 392 msec, corrected QT (QTc) using Bazett's formula was 431 msec (Figure 1).
case_images: Electrocardiogram at peak exertion demonstrating left bundle branch block morphology.
case_images: CRIVAM2014-204805.002.jpg
case_images: PMC3971859_01_CRIVAM2014-204805.002.jpg
case_images: fig2
case_images: She was referred for exercise stress testing using the Bruce protocol during which she developed a left bundle branch block (LBBB) with a QRS duration of 120 msec at a heart rate of 112 beats per minute (bpm) (Figure 2).
case_images: Plot of maximum normally conducted heart rates over time, demonstrating an increase in maximum rate with regular exercise training (red) and a decrease with nonadherence to regular training (blue).
case_images: CRIVAM2014-204805.003.jpg
case_images: PMC3971859_01_CRIVAM2014-204805.003.jpg
case_images: fig3
case_images: After three months of regular exercise training with 30-minute sessions per day for five days a week, the patient's symptoms improved with development of LBBB and chest pain at a considerably higher heart rate of 150 bpm (Figure 3).