Ventricular tachycardia initiation patterns on electrograms of implantable defibrillator devices

Abstract Introduction Sudden cardiac death is an unexpected death from a cardiac origin attributed by arrhythmias such as ventricular fibrillation (VF) and ventricular tachycardia (VT). The predominant treatment to terminate VT and VF is the implantation of an implantable cardioverter defibrillator (ICD). Currently, VT initiation in specific and small cohorts such as structural heart disease and reduced left ventricular ejection fraction patients have been explored. However, there is limited literature comparing the association between VT initiation patterns and defibrillators therapy outcome. This study aimed to investigate the most prevalent type of VT initiation from stored electrograms on ICDs and to explore the association between VT initiation pattern and therapy outcome (i.e., the ability to terminate VT). Method 344 stored electrograms amongst 65 patients from an existing database were visually inspected to classify VT initiation pattern as sudden onset (not preceded by premature ventricular complexes), non-sudden onset (preceded by premature ventricular complexes) and pacing-induced (device induced). Wilcoxon rank sum and Fisher’s Exact tests were used to assess differences between these groups. Mixed-effect logistic regression models accounting for multiple events occurring in individual patients were used to investigate association between the VT initiation pattern and therapy outcome. Results The mean age for the study group was 53±20 years and 54 (83%) subjects were males. Aetiology includes: 29 ischemic heart disease (45%), 10 hypertrophic cardiomyopathy (15%), 8 dilated cardiomyopathy (12%) and 18 other conditions (28%). Non-sudden onset VT (51%) was the most prevalent type of VT initiation pattern on defibrillators followed by sudden onset (44%) and pacing induced (5%). Non-sudden onset was 3 times more likely than the other 2 groups combined to be associated with unsuccessful therapies with an OR: 3.05 (95% confidence interval: 1.14, 8.15); p =0.03. There was no association between pacing-induced onset and unsuccessful therapies with an OR: 0.33 (95% confidence interval: 0.03, 3.33); p = 0.35. No association was identified for any of the three initiation patterns versus the other two combined and unsuccessful therapies when mixed-effect models were constructed. Discussion/ Conclusion: This study is consistent with other findings showing that non-sudden onset (51%) is the most prevalent VT onset. Pacing-induced VT accounted for 5% of VT with the predominant reason for initiation being undersensing of R-waves leading to pacing on the T-wave. This study reiterates the importance of programming strategies to prevent pacing induced VT. No associations were found with VT initiation and therapy outcome with mixed-effect models, possibly due to pseudo-replication being a limitation of this study. Prospective studies should be carried out in future to attempt to maximise success rate and establish the most effective treatment in ICDs.