Asystole and severe bradycardia in preterm infants

Transient episodes of apnea and bradycardia are common in preterm infants. Pronounced asystole or sinus arrest, however, is relatively rare and the clinical significance of such events is unknown. Objective: The purpose of our study was to: (1) evaluate the prevalence of severe bradycardic and asystolic events in infants studied with polygraphic cardiorespiratory monitoring, (2) characterize these events, and (3) correlate the events with other clinical findings. Methods: A total of 583 studies were performed in 454 preterm infants at a post-conceptional age 37.4 ± 2.5 (range 34-42 weeks). Asystolic pauses were defined as no QRS complex for ≥3 s consistent with a heart rate <20 beats per minute (bpm). Severe bradycardia was defined as no QRS for ≥2 s consistent with a heart rate of 21-30 bpm. Results: Eight infants (29.5 ± 3.9 weeks' gestational age, birth weight 1,283 ± 445 g) met the criteria of having had at least 1 asystolic event (heart rate ≤20 bpm). These infants had a total of 32 episodes of bradycardia ≤30 bpm, of which 22 episodes were classified as asystole. During the asystolic episodes, the P-R interval remained unchanged in 21 of 22 episodes and prolonged in 1. One patient had non-sustained ventricular tachycardia before resumption of normal sinus rhythm. All asystolic events were associated with apnea (mean duration of 17.7 ± 9.4 s) and O₂ saturations fell by 10 ± 6%. A pH probe study was available in 9 of 22 asystolic events and 6 of 10 severe bradycardic events. Gastroesophageal reflux was temporally related to only one asystolic and two bradycardic events. Clinical follow-up of these infants at a mean age of 14 months (range 1-46) reveals no symptomatic sequelae; although 1 infant died from multisystem failure associated with multiple congenital anomalies. Conclusions: Asystolic pauses occur in 1.8% of a selected population of preterm infants who have been experiencing cardiorespiratory events, are related to respiratory pauses, and appear to have a benign long-term outcome, although future study should incorporate long-term neurodevelopmental outcome.