Electrocardiographic changes by accidental hypothermia in an urban and a tropical region

Electrocardiogram Features in Non-Cardiac Diseases: From Mechanisms to Practical Aspects

Despite the noteworthy advancements and the introduction of new technologies in diagnostic tools for cardiovascular disorders, the electrocardiogram (ECG) remains a reliable, easily accessible, and affordable tool to use. In addition to its crucial role in cardiac emergencies, ECG can be considered a very useful ancillary tool for the diagnosis of many non-cardiac diseases as well. In this narrative review, we aimed to explore the potential contributions of ECG for the diagnosis of non-cardiac diseases such as stroke, migraine, pancreatitis, Kounis syndrome, hypothermia, esophageal disorders, pulmonary embolism, pulmonary diseases, electrolyte disturbances, anemia, coronavirus disease 2019, different intoxications and pregnancy.

Cold pressor stress effects on cardiac repolarization

The cold pressor test (CPT) elicits strong cardiovascular reactions via activation of the sympathetic nervous system (SNS), yielding subsequent increases in heart rate (HR) and blood pressure (BP). However, little is known on how exposure to the CPT affects cardiac ventricular repolarization. Twenty-eight healthy males underwent both a bilateral feet CPT and a warm water (WW) control condition on two separate days, one week apart. During pre-stress baseline and stress induction cardiovascular signals (ECG lead II, Finometer BP) were monitored continuously. Salivary cortisol and subjective stress ratings were assessed intermittently. Corrected QT (QTc) interval length and T-wave amplitude (TWA) were assessed for each heartbeat and subsequently aggregated individually over baseline and stress phases, respectively. CPT increases QTc interval length and elevates the TWA. Stress-induced changes in cardiac repolarization are only in part and weakly correlated with cardiovascular and cortisol stress-reactivity. Besides its already well-established effects on cardiovascular, endocrine, and subjective responses, CPT also impacts on cardiac repolarization by elongation of QTc interval length and elevation of TWA. CPT effects on cardiac repolarization share little variance with the other indices of stress reactivity, suggesting a potentially incremental value of this parameter for understanding psychobiological adaptation to acute CPT stress.

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.

Hypothermia and cardiac electrophysiology: a systematic review of clinical and experimental data

Moderate therapeutic hypothermia procedures are used in post-cardiac arrest care, while in surgical procedures, lower core temperatures are often utilized to provide cerebral protection. Involuntary reduction of core body temperature takes place in accidental hypothermia and ventricular arrhythmias are recognized as a principal cause for a high mortality rate in these patients. We assessed both clinical and experimental literature through a systematic literature search in the PubMed database, to review the effect of hypothermia on cardiac electrophysiology. From included studies, there is common experimental and clinical evidence that progressive cooling will induce changes in cardiac electrophysiology. The QT interval is prolonged and appears more sensitive to decreases in temperature than the QRS interval. Severe hypothermia is associated with more pronounced changes, some of which are proarrhythmic. This is supported clinically where severe accidental hypothermia is commonly associated with ventricular fibrillation or asystole. J-waves in human electrocardiogram recordings are regularly but not always observed in hypothermia. Its relation to ventricular repolarization and arrhythmias is not obvious. Little clinical data exist on efficacy of anti-arrhythmic drugs in hypothermia, while experimental data show the potential of some agents, such as the class III antiarrhythmic bretylium. It is apparent that QT-prolonging drugs should be avoided.

Electrocardiographic changes during therapeutic hypothermia: observational data from a single centre

Background

Therapeutic hypothermia is recommended to reduce the risk of hypoxic brain damage and improve short-term survival after cardiac arrest. It also temporarily affects the cardiac conduction system. The aim of this study was to evaluate electrocardiographic changes during therapeutic hypothermia and their impact on the outcome.

Materials and methods

This retrospective analysis involved 26 patients who underwent therapeutic hypothermia after cardiac arrest in Vilnius University Hospital Santaros Klinikos from 2011 to 2015.

Results

During cooling, a significant reduction in the heart rate (p = 0.013), shortening of QRS complex duration (p = 0.041), and prolongation of the QTc interval (p < 0.001) were observed. During the cooling period, five patients had subtle Osborn waves, which disappeared after rewarming. The association between electrocardiographic changes during cooling and unfavourable neurological outcome or in-hospital mortality was non-significant.

Conclusions

Therapeutic hypothermia after cardiac arrest causes reversible electrocardiographic changes that do not increase the risk of in-hospital mortality or unfavourable neurological outcomes.

Modeling hypothermia induced effects for the heterogeneous ventricular tissue from cellular level to the impact on the ECG

Hypothermia has a profound impact on the electrophysiological mechanisms of the heart. Experimental investigations provide a better understanding of electrophysiological alterations associated with cooling. However, there is a lack of computer models suitable for simulating the effects of hypothermia in cardio-electrophysiology. In this work, we propose a model that describes the cooling-induced electrophysiological alterations in ventricular tissue in a temperature range from 27°C to 37°C. To model the electrophysiological conditions in a 3D left ventricular tissue block it was essential to consider the following anatomical and physiological parameters in the model: the different cell types (endocardial, M, epicardial), the heterogeneous conductivities in longitudinal, transversal and transmural direction depending on the prevailing temperature, the distinct fiber orientations and the transmural repolarization sequences. Cooling-induced alterations on the morphology of the action potential (AP) of single myocardial cells thereby are described by an extension of the selected Bueno-Orovio model for human ventricular tissue using Q10 temperature coefficients. To evaluate alterations on tissue level, the corresponding pseudo electrocardiogram (pECG) was calculated. Simulations show that cooling-induced AP and pECG-related parameters, i.e. AP duration, morphology of the notch of epicardial AP, maximum AP upstroke velocity, AP rise time, QT interval, QRS duration and J wave formation are in good accordance with literature and our experimental data. The proposed model enables us to further enhance our knowledge of cooling-induced electrophysiological alterations from cellular to tissue level in the heart and may help to better understand electrophysiological mechanisms, e.g. in arrhythmias, during hypothermia.

Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM)

BACKGROUND

This paper provides an up-to-date review of the management and outcome of accidental hypothermia patients with and without cardiac arrest.

METHODS

The authors reviewed the relevant literature in their specialist field. Summaries were merged, discussed and approved to produce this narrative review.

RESULTS

The hospital use of minimally-invasive rewarming for non-arrested, otherwise healthy, patients with primary hypothermia and stable vital signs has the potential to substantially decrease morbidity and mortality for these patients. Extracorporeal life support (ECLS) has revolutionised the management of hypothermic cardiac arrest, with survival rates approaching 100 % in some cases. Hypothermic patients with risk factors for imminent cardiac arrest (temperature <28 °C, ventricular arrhythmia, systolic blood pressure <90 mmHg), and those who have already arrested, should be transferred directly to an ECLS-centre. Cardiac arrest patients should receive continuous cardiopulmonary resuscitation (CPR) during transfer. If prolonged transport is required or terrain is difficult, mechanical CPR can be helpful. Delayed or intermittent CPR may be appropriate in hypothermic arrest when continuous CPR is impossible. Modern post-resuscitation care should be implemented following hypothermic arrest. Structured protocols should be in place to optimise pre-hospital triage, transport and treatment as well as in-hospital management, including detailed criteria and protocols for the use of ECLS and post-resuscitation care.

CONCLUSIONS

Based on new evidence, additional clinical experience and clearer management guidelines and documentation, the treatment of accidental hypothermia has been refined. ECLS has substantially improved survival and is the treatment of choice in the patient with unstable circulation or cardiac arrest.

The Role of Transmural Repolarization Gradient in the Inversion of Cardiac Electric Field: Model Study of ECG in Hypothermia

BACKGROUND

The changes in ventricular repolarization gradients lead to significant alterations of the electrocardiographic body surface T waves up to the T wave inversion. However, the contribution of a specific gradient remains to be elucidated. The objective of the present investigation was to study the role of the transmural repolarization gradient in the inversion of the body surface T wave with a mathematical model of the hypothermia-induced changes of ventricular repolarization.

METHODS

By means of mathematical simulation, we set the hypothermic action potential duration (APD) distribution on the rabbit ventricular epicardium as it was previously experimentally documented. Then the parameters of the body surface potential distribution were tested with the introduction of different scenarios of the endocardial and epicardial APD behavior in hypothermia resulting in the unchanged, reversed or enlarged transmural repolarization gradient.

RESULTS

The reversal of epicardial repolarization gradients (apicobasal, anterior-posterior and interventricular) caused the inversion of the T waves regardless of the direction of the transmural repolarization gradient. However, the most realistic body surface potentials were obtained when the endocardial APDs were not changed under hypothermia while the epicardial APDs prolonged. This produced the reversed and increased transmural repolarization gradient in absolute magnitude. The body surface potentials simulated under the unchanged transmural gradient were reduced in comparison to those simulated under the reversed transmural gradient.

CONCLUSIONS

The simulations demonstrated that the transmural repolarization gradient did not play a crucial role in the cardiac electric field inversion under hypothermia, but its magnitude and direction contribute to the T wave amplitude.

A comprehensive literature review on hypothermia and early extubation following coronary artery bypass surgery

PURPOSE

The purpose of this study was to comprehensively review the literature addressing the physiological effects of hypothermia and its association with the appropriate core body temperature for extubation following coronary artery bypass surgery.

METHODS

The electronic databases MEDLINE, CINAHL and Web of Science via OVID were used to identify studies for the literature review. Search words used included 'core temperature', 'arrhythmia', 'cardiac', 'cardiac surgery', 'hypothermia', 'extubation', 'temperature', 'rewarming', and 'shivering'.

RESULTS

The literature search yielded 55 articles that met our inclusion criteria. No studies specifically identified the benefit of extubation at 36.5 ° C. Although temperatures varied, arrhythmias resulting from hypothermia were not reported until core body temperature dropped below 33 ° C.

CONCLUSION

This comprehensive literature review suggests extubation at lower temperatures (between 34 ° C and 36 ° C) may be viable if shivering and other factors known to contribute to myocardial stress can be controlled. These findings offer the possibility of earlier extubation which may promote beneficial health outcomes.

Sudden cardiac death in a dialysis patient: hyperkalemia reconsidered

BACKGROUND

To many physicians, hyperkalemia is the first diagnosis ascribed to any patient with end-stage renal disease and abnormal electrocardiographic morphologies or dysrhythmias.

CASE REPORT

A 52-year-old man with end-stage renal disease presented in cardiac arrest. The patient was initially presumed to have hyperkalemia, based on the appearance of wide QRS complexes on the monitor. The diagnosis of hyperkalemia was incorrect; the patient was severely hypokalemic and suffered recurrent episodes of ventricular fibrillation and torsades de pointes.

WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS

An emergency physician's differential diagnosis of sudden cardiac arrest in the patient with end-stage renal disease should not be limited to hyperkalemia and myocardial infarction. Hypokalemia should also be considered. Hypokalemia may be an under-recognized cause of sudden cardiac death in this patient population.

Cardiac repolarization and autonomic regulation during short-term cold exposure in hypertensive men: an experimental study

OBJECTIVES

The aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.

METHODS

We conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55-65 years) who underwent whole-body cold exposure (15 min exposure to temperature -10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.

RESULTS

Short-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.

CONCLUSIONS

Short-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02007031.

Electrocardiographic changes in hypothermia: a review

Hypothermia is a common environmental emergency encountered by physicians and is associated with a variety of electrocardiographic (ECG) abnormalities. The classic and well-known ECG manifestations of hypothermia include the presence of J (Osborn) waves, interval (PR, QRS, QT) prolongation, and atrial and ventricular arrhythmias. There are less well defined and known ECG signs of hypothermia, which in fact may simulate findings of acute coronary ischemia, Brugada syndrome, or even pericarditis. Although classical ECG changes seen in hypothermia certainly serve as an important clinical clue for prompt identification and management of this easily curable life-threatening entity, physicians should, however, be able to maintain a high suspicion for recognition and differentiation of less common ECG abnormalities encountered in hypothermia. This article aims to provide a detailed review of all the potential ECG abnormalities that may be encountered in accidental and iatrogenic hypothermia.

Overt and latent cardiac effects of ozone inhalation in rats: evidence for autonomic modulation and increased myocardial vulnerability

BACKGROUND

Ozone (O₃) is a well-documented respiratory oxidant, but increasing epidemiological evidence points to extrapulmonary effects, including positive associations between ambient O₃ concentrations and cardiovascular morbidity and mortality.

OBJECTIVE

With preliminary reports linking O₃ exposure with changes in heart rate (HR), we investigated the hypothesis that a single inhalation exposure to O₃ will cause concentration-dependent autonomic modulation of cardiac function in rats.

METHODS

Rats implanted with telemeters to monitor HR and cardiac electrophysiology [electrocardiography (ECG)] were exposed once by whole-body inhalation for 4 hr to 0.2 or 0.8 ppm O₃ or filtered air. A separate cohort was tested for vulnerability to aconitine-induced arrhythmia 24 hr after exposure.

RESULTS

Exposure to 0.8 ppm O₃ caused bradycardia, PR prolongation, ST depression, and substantial increases in atrial premature beats, sinoatrial block, and atrioventricular block, accompanied by concurrent increases in several HR variability parameters that were suggestive of increased parasympathetic tone. Low-O₃ exposure failed to elicit any overt changes in autonomic tone, heart rhythm, or ECG. However, both 0.2 and 0.8 ppm O₃ increased sensitivity to aconitine-induced arrhythmia formation, suggesting a latent O₃-induced alteration in myocardial excitability.

CONCLUSIONS

O₃ exposure causes several alterations in cardiac electrophysiology that are likely mediated by modulation of autonomic input to the heart. Moreover, exposure to low O₃ concentrations may cause subclinical effects that manifest only when triggered by a stressor, suggesting that the adverse health effects of ambient levels of air pollutants may be insidious and potentially underestimated.

Hypothermia with pneumonia: a rare presentation of brucellosis

OBJECTIVE

To report a very rare form of brucellosis presenting with hypothermia and pneumonia.

CLINICAL PRESENTATION AND INTERVENTION

A 41-year-old male shepherd presented with a depressed level of consciousness. Clinically, his rectal temperature was 29.5°C, and he was cold, apathetic, hyporeflexic, and hypotensive, with atrial fibrillation. He had clinical and radiological evidence of bilateral bronchopneumonia. Blood culture and serologic testing were positive for Brucella melitensis. The patient recovered completely after proper management of the hypothermia and treatment of the brucellosis with antibiotics (doxycycline 100 mg orally twice daily for 6 weeks and streptomycin 1 g i.m. daily for 21 days).

CONCLUSION

This case shows that brucellosis should be considered in the differential diagnosis of septicemic patients presenting with hypothermia.

Diffuse ST segment depression from hypothermia

Hypothermia is known to cause specific electrocardiographic (EKG) changes such as Osborne waves and bradycardia. We report diffuse ST segment depression, an atypical EKG change, in a patient with a core temperature of 29.4°C (85°F). This patient had no previous cardiovascular pathology, and his EKG changes resolved gradually with aggressive warming. We also discuss the pathophysiology and clinical significance of ST depression in the general population and the typical EKG changes in hypothermia patients.