Introduction: Ventricular tachycardia and fibrillation are both life-threatening arrhythmias. Implantable cardioverter defibrillators (ICDs) can be used to cardiovert these arrhythmias via high-voltage therapy. However, ICDs must distinguish life-threatening arrhythmias from physiological cardiac rhythms, doing so via algorithms specific to device type and manufacturer. The aim of this service evaluation was to determine rates of appropriate and inappropriate therapies (IT) delivered between single and dual chamber (SC and DC) ICDs, across a range of manufacturers with standardised settings.
Methods: A retrospective service evaluation was conducted at a tertiary centre. The population included all patients with SC and DC devices implanted between 1 January 2017 and 1 May 2020. Device parameters and events were assessed from remote monitoring data and electronic health records. Categorical data comparisons were made using Fisher’s tests. The audit was registered with the clinical effectiveness unit (CEU).
Results: A total of 701 patients with SC (n=217, 31%) and DC (n=484, 69%) ICDs were included (74.1% male, mean age 63 ± 15.8 years). Mean follow-up periods for SC and DC devices were both 20 ± 10 months. A total of 20 (9%) SC devices delivered appropriate therapies compared with 54 (11%) DC devices. Differences in rate of IT across device type did not meet significance, occurring in 1% and 3% in SC and DC devices, respectively (OR 0.29, 95% CI 0.07–1.20; p=0.08). The most common cause of IT was atrial fibrillation and atrial tachycardia: 11/15 (73%) incidences in DC and 2 (100%) incidences in SC devices. Other causes of IT in DC devices were attributed to the incorrect classification of ventricular tachycardia (20%) and ventricular fibrillation. The mean follow-up across manufacturers (Boston Scientific, Medtronic, Biotronik and Abbott) was 21 ± 10 months, 23 ± 10 months, 27 ± 10 months and 17 ± 10 months, respectively. Boston Scientific accounted for the highest proportion of devices at 55%, with Abbott, Medtronic and Biotronik accounting for 25%, 16% and 4%, respectively. There were small differences in IT burden between manufacturers: Boston Scientific (3.4%), Medtronic (2.7%), Abbott (0.6%) and 0% of Biotronik devices; however, these did not meet statistical significance during pairwise comparison (all p>0.05). A trend towards differences in IT rates between the two largest manufacturers in the cohort (Abbott and Boston Scientific OR 0.16, 95% CI 0.015–1.001; p=0.076) may warrant further investigation during longer follow-up.
Conclusion: There was no difference in rate of IT between SC and DC device types, or across manufacturers. However, a trend towards differences in rate of IT between the largest manufacturers in the cohort indicates an area of potential further investigation. IT of atrial arrhythmias was the leading cause of IT.