The atrial repolarization wave: A newly described finding in the electrocardiogram of the mouse (Mus musculus)

Summary The present studies reveal, for the first time, that an atrial repolarization, or Ta, wave is a characteristic feature of the electrocardiogram of the laboratory mouse. This slowly inscribed wave, which immediately follows the P wave, was clearly visible in the electrocardiograms of all 79 adult mice (Swiss-Webster, ICR, and Strong A strains) studied. Like the Q-T interval, the P-Ta interval relative to heart rate is remarkably short in the mouse compared with that for man. The determination of cardiac temporal relations from an esophageal lead and from phonocardiograms, the sensitivity of the Ta wave to pharmacological and metabolic interventions before the P wave changed, and postnatal developmental studies clearly differentiated the Ta wave-from the atrial depolarization, or P, wave. The Ta wave amplitude was initially heightened by hyperkalemia and was increased slightly by cardioacceleration produced by right atrial electrical pacing. The Ta wave was progressively depressed and then inverted by a cardiac glycoside and by asphyxia. Newborn mice generally, but not always, lacked a visible Ta wave. At 8 days after birth, a Ta wave of low amplitude was present and the P-Ta interval was long. During the remaining juvenile stage, the Ta amplitude increased and the P-Ta and Q-T intervals progressively shortened, reaching adult levels by three to four weeks of age. The present study also demonstrates, for the first time, a diastolic sound, either an S 4 or an S 4 summated with an S 3 , and inspiratory splitting and expiratory fusion of the second heart sound in the mouse. In conclusion, the mouse has the species characteristics of a distinctive Ta wave and a short P-Ta interval (as well as Q-T interval) on the electrocardiogram.