The association between body temperature and electrocardiographic parameters in normothermic healthy volunteers

Background

Previous studies reported that hypo‐ and hyperthermia are associated with several atrial and ventricular electrocardiographical parameters, including corrected QT (QTc) interval. Enhanced characterization of variations in QTc interval and normothermic body temperature aids in better understanding the underlying mechanism behind drug induced QTc interval effects. The analysis’ objective was to investigate associations between body temperature and electrocardiographical parameters in normothermic healthy volunteers.

Methods

Data from 3023 volunteers collected at our center were retrospectively analyzed. Subjects were considered healthy after review of collected data by a physician, including a normal tympanic body temperature (35.5‐37.5°C) and in sinus rhythm. A linear multivariate model with body temperature as a continuous was performed. Another multivariate analysis was performed with only the QT subintervals as independent variables and body temperature as dependent variable.

Results

Mean age was 33.8 ± 17.5 years and mean body temperature was 36.6 ± 0.4°C. Body temperature was independently associated with age (standardized coefficient [SC] = −0.255, P < .001), female gender (SC = +0.209, P < .001), heart rate (SC = +0.231, P < .001), P‐wave axis (SC = −0.051, P < .001), J‐point elevation in lead V4 (SC = −0.121, P < .001), and QTcF duration (SC = −0.061, P = .002). In contrast, other atrial and atrioventricular (AV) nodal parameters were not independently associated with body temperature. QT subinterval analysis revealed that only QRS duration (SC = −0.121, P < .001) was independently associated with body temperature.

Conclusion

Body temperature in normothermic healthy volunteers was associated with heart rate, P‐wave axis, J‐point amplitude in lead V4, and ventricular conductivity, the latter primarily through prolongation of the QRS duration.

Osborn wave in hypothermia and relation to mortality

BACKGROUND & AIM

The aim of this study was to compare hypothermia patients with and without an Osborn wave (OW) in terms of physical examination findings, laboratory results, and clinical survival.

METHODS

The study was carried out retrospectively on hypothermic patients. The hypothermic patients were divided into two groups. Group 1 comprised patients with OW on electrocardiogram (ECG), and Group 2 comprised patients without OW on ECG. The Mann-Whitney U test was used to compare the two groups, and the relationships between the variables and the presence of OW and mortality were analyzed with ANOVA. A value of p < 0.05 was considered statistically significant.

RESULTS

OW was detected on ECG of 41.9% of the patients (Group 1). The mean body temperature was 30.8 ± 4.1 °C in Group 1 and 33.3 ± 1.6 °C in Group 2 (p = 0.106). The mean creatinine level was 1.01 ± 0.6 mg/dl in Group 1 and 0.73 ± 0.5 mg/dl in Group 2 (p = 0.046). The mean bicarbonate level was 15.9 ± 3.8 mmol/l in Group 1 and 18.6 ± 3.5 mmol/l in Group 2 (p = 0.038). A relationship was determined between the presence of OW and pH, bicarbonate, and creatinine levels (p = 0.026; 0.013; 0.042, respectively). The mortality rate was 69.2% in Group 1 and 77.8% in Group 2 (p = 0.689).

CONCLUSION

Although there is a relationship between the decrease in bicarbonate levels, changes in kidney functions that cause acidosis, and the presence of OW, it has no effect on mortality. The presence of OW in hypothermic patients is insufficient to make a decision regarding mortality.

Dynamicity of hypothermia-induced J waves and the mechanism involved

BACKGROUND

J waves develop during hypothermia, but the dynamicity of hypothermia-induced J waves is poorly understood.

OBJECTIVE

The purpose of this study was to investigate the mechanism of the rate-dependent change in the amplitude of hypothermia-induced J waves.

METHODS

Nineteen patients with severe hypothermia were included (mean age 70 ± 12 years; 16 men [84.2%]). The rectal temperature at the time of admission was 27.8° ± 2.5°C. In addition to prolonged PR, QRS complex, and corrected QT intervals, the distribution of prominent J waves was widespread in all 19 patients.

RESULTS

Nine patients showed changes in RR intervals. When the RR interval shortened from 1353 ± 472 to 740 ± 391 ms (P = .0002), the J-wave amplitude increased from 0.50 ± 0.29 to 0.61 ±0.27 mV (P = .0075). The J-wave amplitude increased in 7 patients (77.8%) and decreased in 2 patients (22.2%) after short RR intervals. The augmentation of J waves at short RR intervals was associated with a significant prolongation of ventricular activation time (35 ± 5 ms vs 46 ± 5 ms; P = .0020), suggesting accentuated conduction delay. Increased conduction delay at short RR intervals was suggested to accentuate the phase 1 notch of the action potential and J waves in hypothermia. None developed ventricular fibrillation, and in 2 of 9 patients with atrial fibrillation, atrial fibrillation persisted after rewarming to normothermia.

CONCLUSION

J waves in severe hypothermia were augmented after short RR intervals in 7 patients as expected for depolarization abnormality, whereas 2 patients showed a bradycardia-dependent augmentation as expected for transient outward current-mediated J waves. Increased conduction delay at short RR intervals can be responsible for the accentuation of the transient outward current and J waves during severe hypothermia.

[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.