Subcutaneous and transvenous implantable cardioverter defibrillators : developing an individualised approach to assessment and treatment

• Main Author: Wilson, David G.
• Other Authors: Dimitrov, Borislav ; Morgan, John ; Roderick, Paul
• Published: University of Southampton 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.729668

In recent years the subcutaneous implantable cardioverter-defibrillator (S-ICD) has emerged as a novel technology which offers an alternative choice to the traditional transvenous implantable cardioverter-defibrillator (TV-ICD) in treatment and prevention of sudden cardiac death. Early experience with the S-ICD however has highlighted that its capacity to accurately sense the cardiac signal can be challenged, in particular with regard to the risk of varying amplitude of signals and risk of T wave oversensing. S-ICD sensing is therefore an important weakness of this technology which this thesis addresses. Initially only a relatively small group of patients were thought to be suitable for S-ICD, in particular patients with difficult venous anatomy or young patients. Therefore I explored how the important ECG parameters in S-ICD sensing, the R wave, the T wave and the R:T ratio, vary when measured from a right compared to a left parasternal lead position in a population of patients with complex congenital heart disease and normal controls. I go on to explore how the R wave, T wave and R:T ratio in the same patient population vary with posture and discuss how this relates to potentially clinically important in relation to S-ICD sensing. As the sensed S-ICD signal resembles the signal measured with a standard 12 lead ECG, I go on to evaluate what are the ECG predictors of T-wave oversensing are. Lastly, I explore how application of mathematical vector transformation techniques can help reconstruct an 8 lead ECG from 2 S-ICD vectors, and from then create a 12-lead ECG, and I discuss how this technique may potentially help solve some sensing problems related to the S-ICD. Within this thesis, I demonstrate that much could be done at an individual level (optimise lead position, identify patients at risk of T wave oversensing and using vector transformation to reduce the likelihood of inappropriate therapy) in order to maximise the potential benefit (and reduce the unwanted consequences) of S-ICDs. This thesis has advanced the understanding of how to improve therapy to treat SCD by reducing the unwanted events of S-ICD therapy by developing a concept of a tailored assessment of patient’s suitability for ICD therapy.