Dispersion of the corrected QT interval in acute carbon monoxide poisoning

Carbon monoxide (CO) poisoning is known to cause myocardial toxicity and life-threatening arrhythmias. Corrected QT dispersion (QTdc) of the ECG is an indirect measure of heterogeneity of ventricular repolarisation, which may contribute to ventricular arrhythmias.

The aim of the study was to evaluate the relationship between the carboxyhemoglobin (COHb) level and QTdc during carbon monoxide poisoning.

This study was prospectively performed in 104 patients who diagnosed CO intoxication. Patients were assigned to two groups according to COHb levels < 25% (Group I, n = 32) or COHb > 25% (Group II, n = 72). In each ECG lead, the QT interval and QRS duration were measured in the two groups and corrected for heart rate (QTc) using Bazett's formula (QT/RR1/2). QTdc is then the difference between the leads with the shortest and longest QTc intervals. Measurement of QT intervals were calculated at admission and in 24-hour and 48-hour ECGs after admission. Cardiac enzymes were measured at each stage. The myocardial perfusion after exercise and at rest 4 hours after exercise were determined in all patients 1 week after admission.

QT, QTc and QTd intervals were not significantly different in both of groups each stage whereas the values of the QTdc after 24 hours were significantly greater than QTdc at admission in Group II but not in Group I. Comparison of QTdc for the two groups demonstrated significant differences after 24 hours (P < 0.05) (Table 1). Plasma creatinine phosphokinase (CPK) and CPK-MB levels at admission, and 24 and 48 hours later in Group II were significantly higher than the other group (P < 0.05). Seven patients in Group I and 23 patients in Group II had an extent of myocardial ischemia on scintigraphy.

Table 1

The reduced threshold for arrhythmias in CO poisoning may be due to inhomogeneous repolarization of ventricles, assessed by QTdc. Measuring QTdc for monitoring after CO poisoning may be suggestive of the potential danger of high levels of COHb to cardiac-disabled individuals.