Severe QTc prolongation under mild hypothermia treatment and incidence of arrhythmias after cardiac arrest--a prospective study in 34 survivors with continuous Holter ECG

Background

Mild hypothermia treatment (32-34 °C) in survivors after cardiac arrest (CA) is clearly recommended by the current guidelines. The effects of cooling procedure towards QT interval have not been evaluated so far outside of case series. In a prospective study 34 consecutive survivors after cardiac arrest were continuously monitored with Holter ECG over the first 48 h.

Patients and methods

A total of 34 patients were analysed and received mild therapeutic hypothermia treatment (MTH) according to the current guidelines and irrespective of the initial rhythm. At admission to hospital and in the field in case of OHCA, a 12-lead ECG was performed in all patients.

Results

During cooling the incidence of ventricular tachycardia was low (8.8%) and in none of the patients Torsade de pointes occurred. The QTc interval was within normal range at first patient contact with EMS in the field (440.00 ms; IQR 424.25-476.75; n = 17) but during hypothermia treatment the QTc interval was significantly prolonged at 33 °C after 24 h of cooling (564.47 ms; IQR 512.41-590.00; p = 0.0001; n = 34) and decreased after end of hypothermia to baseline levels (476.74 ms; 448.71-494.97; p = 0.15).

Conclusion

The QTc interval was found to be significantly prolonged during MTH treatment, and some severe prolongations >670 ms were observed, without a higher incidence of life-threatening arrhythmias, especially no Torsade des pointes were detected. However, routine and frequent ECG recording with respect to the QTc interval should become part of any hypothermia standard operation protocol and should be recommended by official guidelines.