Background: There is an unmet need for simple tools for monitoring QT intervals. The feasibility of measuring the QT interval on the single‑lead subcutaneous electrocardiogram (subECG) recorded and transmitted by implantable cardiac monitors (ICMs) has never been tested.
Methods: We performed a standard ECG in patients who had already been implanted with a long sensing vector ICM (BIOMONITOR, Biotronik SE&Co.) to calculate the corrected QT interval in lead II (QTc ECG). The QTc was then evaluated on the subECG provided by ICM both by using the programmer printout (QTc subECG) and the snapshot transmitted via home monitoring (QTc HM). Values were compared with Bland-Altman analyses.
Results: The study cohort consisted of 23 ICM recipients (age 58 ± 19 years, 35% female) implanted mainly for unexplained syncope (78%). The mean QTc ECG interval was 404 ± 31 ms. The T-wave was visible and QTc could be calculated in all patients using the ICM programmer printout and in 21 (91%) patients remotely. The QTc subECG and QTc HM were 405 ± 34 and 406 ± 32 ms. Compared to the QTc ECG, Bland-Altman analyses revealed a bias of -0.9 (95% confidence interval: -6.8/4.9) ms and 0.1 (-12.7/12.9) ms for QTc subECG and QTc HM, respectively.
Conclusions: The QTc interval can be reliably estimated on in-person and remote subECG in most patients without bias compared to the ECG lead II assessment. This technology has the potential to facilitate remote QT interval monitoring.
Keywords: Implantable cardiac monitor; Implantable loop recorder; QT prolongation; QT/QTc interval; Telemedicine.
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