Ambulatory Cardiac Monitoring in Infants with Supraventricular Tachycardia

Background: Supraventricular tachycardia (SVT) is a frequent cause of tachyarrhythmia in infants < 1 year of age and ambulatory cardiac monitoring is an important tool for initial diagnosis and follow-up of these patients. While infants with SVT are frequently followed with intermittent outpatient cardiac monitoring, the utility and optimal monitoring length is unknown.

Methods: Retrospective review of all infants ( <12 months of age) who had ambulatory cardiac monitoring (1-30 days) through the Pocket ECG system (MediLynx) between January 2016 - July 2020 was performed. All patients with an ICD-10 code for SVT (I47.1) present at enrollment were analyzed separately. Age, type and length of cardiac monitoring, minimum, maximum and average heart rates, supraventricular and ventricular ectopy and arrhythmia incidence were collected and analyzed.

Results: A total of 594 patients (mean age 3.6 months, 54% M) underwent ambulatory cardiac monitoring (69% 24-hour Holter, 31% extended monitor) during the study period and 170 patients (mean age 3.4 months, 57% M) (63% 24-hour Holter, 37% extended monitor) had the I47.1 ICD-10 code used at enrollment. Forty-nine (8.2%) patients had sustained SVT or non-sustained SVT (nSVT) during the study period, including 20 patients (40.8%) which had the I47.1 ICD-10 code at enrollment. The patients with SVT or nSVT were diagnosed by extended monitoring in 61% and 24-hour Holter monitoring in the remaining 39%. In the overall group, the first episode of SVT or nSVT was diagnosed within 24 hours of monitoring in 42/49 patients (85.7%). One hundred thirty-nine patients had extended monitoring for ≥ 7 days with 24 patients (17%) diagnosed with SVT or nSVT. Within this group, 71% had a diagnostic strip within 24 hours of monitoring and 96% were diagnosed within a week of monitoring. A single patient was diagnosed with arrhythmia at day 15 of monitoring and no patients were diagnosed beyond 15 days. There was no significant difference in minimal, maximal and average minutely heart rate between patients with and without ICD-10 code I47.1 at enrollment or between patients with and without nSVT or SVT.

Conclusion: Despite the low yield, ambulatory cardiac monitors are an important diagnostic tool for infants with SVT. Although the diagnosis of nSVT or SVT was frequently made by extended monitoring, the majority of patients were diagnosed within 24 hours of monitor placement. The ideal monitor length for these patients has yet to be defined, but all patients in our cohort were identified by day 15 of monitoring.