Comparative Outcomes of Subcutaneous and Transvenous Cardioverter-Defibrillators
In the world of cardiac care, implantable cardioverter-defibrillators (ICDs) play a crucial role in treating life-threatening heart rhythms. Two types of ICDs, the subcutaneous implantable cardioverter-defibrillator (S-ICD) and the transvenous ICD (T-ICD), are available. But how do they compare in terms of safety and efficacy? This study from the Chinese Medical Journal (2019) aims to answer that question.
Introduction
The S-ICD is designed as an alternative to conventional implantable defibrillators. It’s safe, effective, and avoids the problems associated with intravascular leads. It’s especially good for young patients, those without venous access for lead placement, or those prone to recurrent lead-related bloodstream infections. Previous studies like the Investigational Device Exemption (IDE) study and the Evaluation of Factors Impacting Clinical Outcomes and Cost Effectiveness of the S-ICD (EFFORTLESS) Registry showed that the S-ICD is highly effective for treating ventricular fibrillation (VF) or ventricular tachycardia (VT). However, long-term comparisons with T-ICD were lacking. The S-ICD has limitations like not being able to provide bradycardia pacing and having a concern for inappropriate therapies due to T-wave oversensing. So, this study set out to compare the efficacy and safety of S-ICD and single-chamber T-ICD.
Methods
Patient Selection
Patients who received an S-ICD at Mayo Clinic between 2012 and 2016 were included. They had indications for ICD implantation according to guidelines and no need for pacing or a history of monomorphic ventricular tachycardia requiring antitachycardia pacing. The decision to implant an S-ICD was based on factors like young age, diagnosis, primary prevention of sudden death, patient preference, and high risk of T-ICD infection or lack of transvenous access.
Matching
Using an ICD database, patients with S-ICD were 1:1 matched with those who received single-chamber T-ICD based on gender, age (±5 years), cardiomyopathy diagnosis, primary vs. secondary prevention, and left ventricular ejection fraction.
Implantation
For S-ICD, patients were screened with the Boston Scientific electrocardiography screening tool. After eligibility, they underwent standard implantation. Two techniques (three-incision and two-incision) were used. Defibrillation was performed with a 65-J shock energy. In the T-ICD group, DFT testing wasn’t routine. After implantation, chest radiography confirmed lead and generator positions.
Programming and Follow-up
In the S-ICD group, devices were programmed in two zones (VT and VF). In the T-ICD group, for primary prevention, there were two zones (VT monitor and VF). Patients had 3-month follow-ups in person and then remote or outpatient follow-ups. Device-related complications were recorded.
Statistical Analysis
Continuous variables were expressed as mean ± standard deviation, and categorical variables with numbers and frequencies. Chi-squared or Fisher exact test compared categorical variables, and t-test or Wilcoxon rank sum test compared continuous variables. Kaplan-Meier method was used for survival and freedom from shock therapies.
Results
Patient Characteristics
172 patients were included (86 S-ICD and 86 T-ICD). Mean age was 45 years, 69.2% male. The most common cardiac condition was hypertrophic cardiomyopathy (HCM, 37.8%). Mean LVEF was 50%.
Implantation Success
All S-ICD patients had successful implantation. In the T-ICD group, mean implant impedance was 693 ± 134V, pacing threshold 0.6 ± 0.2V, and sensing threshold 14.0 ± 7.8mV.
Procedure Complications
At a mean follow-up of 23 ± 15 months, there were no significant differences in device-related infection. Pocket hematoma occurred in two patients in each group. Infective endocarditis was in two T-ICD patients. No lead malfunction in S-ICD, but three lead fractures in T-ICD. Three S-ICD patients had removal/revision (pocket infection and T-wave oversensing). Five T-ICD patients had lead removal (infective endocarditis and lead malfunction).
ICD Therapies
Appropriate ICD therapy rate was 1.2% (S-ICD) vs. 4.7% (T-ICD) (P = 0.368). Inappropriate therapy rate was 9.3% (S-ICD) vs. 3.5% (T-ICD) (P = 0.211). S-ICD had higher T-wave oversensing (9.3% vs. 0%, P = 0.007).
Survival
Survival wasn’t significantly different between groups (P = 1.000). Most deaths were due to heart failure.
Patients with HCM
65 patients had HCM (32 S-ICD, 33 T-ICD). No significant difference in major complications.
Discussion
S-ICD Implant Success
All S-ICD implantations were successful. The two-incision technique was simpler and caused less discomfort. No patients failed DFT testing at 65 J, showing sufficient energy delivery.
Device-Related Complications
Avoiding transvenous lead is an S-ICD advantage, especially for infection-prone patients. No lead malfunction in S-ICD, while lead fractures were in T-ICD.
Appropriate and Inappropriate ICD Shocks
Appropriate therapy rates weren’t different. Inappropriate shocks in S-ICD were due to T-wave oversensing. Pre-implant screening is crucial. In T-ICD, inappropriate shocks were for supraventricular tachycardia and atrial fibrillation.
Survival
Mortality wasn’t different. Most deaths were from heart failure.
Benefit of ICD in HCM Patients
S-ICD is a good alternative for HCM patients to avoid transvenous lead complications. Pre-implant screening is key for HCM patients to avoid T-wave oversensing.
Limitations
This was a retrospective study. Physician bias in S-ICD selection could affect outcomes, but case-matching mitigated this. Sample size wasn’t large.
Conclusion
The S-ICD is as effective as T-ICD, especially in HCM patients. It has fewer major complications. T-wave oversensing is a challenge, but pre-implant screening and programming can help. For more information on this study, visit the original article.
This study provides valuable insights for cardiologists and patients when choosing between S-ICD and T-ICD. It helps in making informed decisions based on patient characteristics and risks.
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