Hypothermia induced alteration of repolarization - impact on acute and long-term outcome: a prospective cohort study

Therapeutic Hypothermia Reduces Peritoneal Dialysis Induced Myocardial Blood Flow Heterogeneity and Arrhythmia

Background: Moderate therapeutic hypothermia (TH) is a well-recognized cardio-protective strategy. The instillation of fluid into the peritoneum provides an opportunity to deliver moderate hypothermia as primary prevention against cardiovascular events. We aimed to to investigate both cardiac perfusion consequences (overall blood flow and detailed assessment of perfusion heterogeneity) and subsequently simulate the associated arrhythmic risk for patients undergoing peritoneal dialysis (PD) induced TH. Methods: Patients underwent high resolution myocardial perfusion scanning using high resolution 256 slice CT scanning, at rest and with adenosine stress. The first visit using the patient's usual PD regimen, on the second visit the same regime was utilized but with cooled peritoneal dialysate at 32°C. Myocardial blood flow (MBF) was quantified from generated perfusion maps, reconstructed in 3D. MBF heterogeneity was assessed by fractal dimension (FD) measurement on the 3D left ventricular reconstruction. Arrhythmogenicity was quantified from a sophisticated computational simulation using a multi-scale human 3D ventricle wedge electrophysiological computational model. Results: We studied 7 PD patients, mean age of 60 ± 7 and mean vintage dialysis of 23.6 ± 17.6 months. There were no significant different in overall segmental MBF between normothermic condition (NT) and TH. MBF heterogeneity was significantly decreased (-14%, p = 0.03) at rest and after stress (-14%, p = 0.03) when cooling was applied. Computational simulation showed that TH allowed a normalization of action potential, QT duration and T wave. Conclusion: TH-PD results in moderate hypothermia leading to a reduction in perfusion heterogeneity and simulated risk of non-terminating malignant ventricular arrhythmias.

A Case of Severe QTc Prolongation During Targeted Temperature Management - What Can We Learn?

BACKGROUND QTc prolongation during targeted temperature management (TTM) post cardiac arrest is a known effect of hypothermia, but its significance is unclear. Several studies suggest that temporary prolongation during TTM is not prognostic and does not potentiate fatal arrhythmias; however, there are limited cases of patients presenting with QTc intervals >700 milliseconds. CASE REPORT We describe a case in which a 57-year-old woman with diabetes, hypertension, and atrial fibrillation presented with concern for stroke. The hospital course was complicated by cardiac arrest requiring TTM, which was stopped early due to significant QTc prolongation of 746 milliseconds. CONCLUSIONS TTM is beneficial post resuscitation for good neurological outcomes, but it also has known adverse cardiac effects such as QTc prolongation. The significance of QTc prolongation during TTM is unclear as several studies have shown no increased incidence of malignant arrhythmias. One case report in the literature describes the incidence of torsades de pointes due to QTc prolongation during TTM. Further study and guidelines regarding electrocardiogram monitoring are needed to determine the importance of QTc prolongation during TTM.

Electrocardiographic changes in patients undergoing targeted temperature management

OBJECTIVES

Targeted temperature management is the recommended therapy for comatose patients after an out-of-hospital cardiac arrest resuscitation due to the reduction in neurological damage and improved outcomes. However, there may result in electrocardiographic instability depending on the degree of targeted temperature management, including minor or life-threatening dysrhythmias or conduction delays. This project aims to describe the frequency of ECG interval changes and clinically relevant dysrhythmias in targeted temperature management patients.

METHODS

This is a retrospective observational study from January 2009 to December 2015. Patients who qualified for the study had a non-traumatic cardiac arrest with a return of spontaneous circulation, received targeted temperature management at 33.5°C for 24 hours followed by 16 hours of rewarming. ECG interval changes and dysrhythmias were recorded immediately after return of spontaneous circulation, and at 24 and 48 hours post return of spontaneous circulation.

RESULTS

A total of 322 patients (age 61.0 ± 16.9 years) had targeted temperature management initiated during the study period, of which 169 had complete data and 13 died prior to completing 24 hours of hypothermia. There were statistically significant changes during targeted temperature management in heart rate (96.7 ± 26.0/min before targeted temperature management; 69.5 ± 19.1/min during, P < 0.001), QRS duration (115.1 ± 32.6 ms before targeted temperature management; 107.8 ± 27.9 ms during targeted temperature management, P < 0.001), and QTc (486.3 ± 52.8 ms before targeted temperature management; 526.9 ± 61.7 ms during targeted temperature management, P < 0.001). There were cardiac dysrhythmias that received treatment during cooling and rewarming.

CONCLUSION

During the period of targeted temperature management and rewarming, we observed few self-limiting ECG interval changes and no clinically significant dysrhythmias in this population during the period of targeted temperature management.

[Hypothermia-induced ECG changes: characteristic, but not specific]

Hypothermia-induced J‑ or so-called Osborn waves can be detected under therapeutic hypothermia in approximately 20-40% of cases. The occurrence of J‑waves in the context of the targeted temperature management after cardiopulmonary resuscitation is characteristic, but not pathognomonic for hypothermia. An electrocardiographic diagnosis under hypothermia after cardiac arrest should always be done with caution due to the various hypothermia-associated electromechanical changes of the myocardium.