Elsevier

Resuscitation

Volume 82, Issue 7, July 2011, Pages 859-862
Resuscitation

Clinical paper
Severe QTc prolongation under mild hypothermia treatment and incidence of arrhythmias after cardiac arrest—A prospective study in 34 survivors with continuous Holter ECG

https://doi.org/10.1016/j.resuscitation.2011.02.043Get rights and content

Abstract

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.

Introduction

Mild therapeutic hypothermia (MTH) has become a routine procedure in survivors after cardiac arrest to improve neurological outcome following the current guidelines by the International Liaison Committee on Resuscitation (ILCOR) and the European Resuscitation Council (ERC).1 A possible transient bradycardia is well known under conditions of hypothermia but only a few studies evaluated the influence of MTH towards heart rate variability and the risk of life-threatening arrhythmias.2, 3 A currently published case series described in four patients undergoing MTH a prolongation of the corrected QT interval (QTc).4 QTc prolongation itself can promote the development of malignant arrhythmias, for example ventricular tachycardia (VT).5

This prospective study was conducted to evaluate the frequency of malignant arrhythmias and to analyse the possible effect of hypothermia on the QTc interval using a continuous Holter ECG during MTH treatment.

Section snippets

Methods

The protocol of this prospective single center study was approved by the local ethics committee on human research and is conducted in accordance with the guidelines of the Declaration of Helsinki. Written informed consent for the use of routine clinical data is part of the standard contract between patients and the Charité Universitätsmedizin Berlin and was obtained from patients or their legal representatives, if available. During the inclusion period between April 2009 and December 2009 a

Baseline characteristics

Median age was 61.5 years (52.0–77.5 IQR) with a majority of OHCA patients (82.3%). In n = 15 the initial rhythm was ventricular fibrillation (VF), n = 12 had asystole and n = 7 suffered cardiac arrest due to pulseless electrical activity. The median number of defibrillations in the VF group was 2 (1.26–4.0 IQR). 20.6% of the patients received initial antiarrhythmic drug treatment with amiodarone during resuscitation (bolus dosage of 300 mg i.v. once) and three patients received 300 mg amiodarone bolus

Discussion

This is the first study revealing a profound prolongation of the QTc interval during MTH without a severe incidence of life-threatening arrhythmias. Furthermore no Torsade de pointes were detected during 48 h Holter ECG monitoring, although a tight correlation was observed of prolonged QTc interval and decreasing temperature level in patients undergoing MTH and only a low incidence of VT has been recorded.

In general, if central body temperature decreases, a decrease of heart rate, spontaneous

Conclusion

According to our results, during mild hypothermia treatment one should closely monitor the QTc interval and should be aware of potentially upcoming malignant arrhythmias. Furthermore, the treatment with drugs causing an additional prolongation of QTc interval, especially anti-arrhythmic drugs and antibiotics that are frequently used in the ICU setting, should be made with caution. However, routine and frequent ECG recording with respect to the QTc interval should become part of any hypothermia

Conflict of interest

None declared.

Acknowledgments

The authors would like to thank Astrid Caemmerer for assistance and support throughout the study. This work was supported by Schiller MediLog GmbH, Wiesbaden, Germany, with technical equipment (Medilog AR12 recorder).

References (14)

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    A high ventricular arrhythmic event rate may be expected in the post-resuscitation population. However, previous studies assessing the arrhythmic risks associated with MTH did not include a control group of patients who were not exposed to MTH [5,10,11]. Thus, it is difficult to distinguish MTH-related ventricular arrhythmias from those arising from multiple additional risk factors other than exposure to hypothermia.

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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2011.02.043.

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