Dynamicity of hypothermia-induced J waves and the mechanism involved
2019
Background
J wavesdevelop during
hypothermia, but the dynamicity of
hypothermia-induced
J wavesis 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
hypothermiawere 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 waveswas widespread in all 19 patients. Results Nine patients showed changes in
RR intervals. When the
RR intervalshortened from 1353 ± 472 to 740 ± 391 ms ( P = .0002), the
J-waveamplitude increased from 0.50 ± 0.29 to 0.61 ±0.27 mV (P = .0075). The
J-waveamplitude increased in 7 patients (77.8%) and decreased in 2 patients (22.2%) after short
RR intervals. The augmentation of
J wavesat short
RR intervalswas 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 intervalswas suggested to accentuate the phase 1 notch of the action potential and
J wavesin
hypothermia. None developed ventricular fibrillation, and in 2 of 9 patients with atrial fibrillation, atrial fibrillation persisted after rewarming to normothermia. Conclusion
J wavesin severe
hypothermiawere augmented after short
RR intervalsin 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 intervalscan be responsible for the accentuation of the transient outward current and
J wavesduring severe
hypothermia.
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