In this study, we assessed the effects of exposure to 4 percent and 6 percent
carboxyhemoglobin on ventricular arrhythmias in 41 subjects (nonsmokers) with documented
coronary artery disease. We used a randomized, double-blind, crossover design. On day 1, a training session with no exposure, the baseline
carboxyhemoglobin level was measured, and a supine bicycle exercise test was done. On days 2 through 4, subjects were exposed to room air, 100 parts per million (ppm)2
carbon monoxide (target, 4 percent blood
carboxyhemoglobin), or 200 ppm
carbon monoxide (target, 6 percent blood
carboxyhemoglobin), and they then did a supine bicycle exercise test.
Radionuclide ventriculography was performed at rest and during exercise. Ambulatory electrocardiogram recordings were made during the four consecutive days to determine the frequency of
premature ventricular contractions at various intervals. The frequency of single
premature ventricular contractions per hour during exercise was significantly greater on the 6 percent
carboxyhemoglobin day than on the room air day (167.72 +/- 37.99 for 6 percent
carboxyhemoglobin compared with 127.32 +/- 28.22 for room air, p = 0.03). The frequency of multiple
premature ventricular contractions per hour was also significantly greater during exercise on the 6 percent
carboxyhemoglobin day compared with the room air day (9.59 +/- 3.70 for the 6 percent
carboxyhemoglobin day compared with 3.18 +/- 1.67 for the room air day, p = 0.02). Patients who developed increased arrhythmias during exercise on the 6 percent
carboxyhemoglobin day were significantly older than those who had no increased
arrhythmia, and, in addition, exercised longer and had a higher peak workload during exercise. No effect of
carbon monoxide exposure was seen on the 4 percent
carboxyhemoglobin day.