Shock Reduction Programming and Heart Function Recovery in Japanese Patients Undergoing Implantable Cardioverter Defibrillator Implantation for Primary Prevention　― A Single-Center Prospective Study ―

Abstract

Background: Although implantable cardioverter-defibrillators (ICD) offer prognostic benefit for patients with reduced left ventricular ejection fraction (LVEF), they remain underused in Japan.

Methods and Results: We analyzed 25 patients who underwent primary prevention ICD implantation. During a median follow-up of 52.6 months, no appropriate shocks occurred, but non-sustained ventricular tachycardia (NSVT) was frequently observed. Two patients underwent antitachycardia pacing. LVEF improved to >35% in nearly half of the patients.

Conclusions: Cardiac resynchronization therapy and pharmacotherapy possibly improved cardiac function. Unnecessary shock delivery programming may have also contributed to the favorable outcomes.

Central Figure

Study highlights. Among 25 Japanese patients with HF undergoing ICD treatment for primary prevention, 80% of patients experienced NSVT, and 8% developed sustained VT, all cases of which were successfully terminated with ATP. CRT and ARNI possibly contributed to the improvement in LVEF, with low rates of all-cause death and HF rehospitalization.

Implantable cardioverter-defibrillators (ICD) mitigate deaths of patients with reduced left ventricular ejection fraction (LVEF), but despite the demonstrated benefit of ICD in Japanese populations,¹ their use remains limited.² This study aimed to assess ventricular arrhythmic events, cardiac function changes, and the impact of shock-reduction programming in real-world patients who received an ICD for primary prevention in Japan.

Methods

This single-center prospective observational study included 25 consecutive patients who underwent ICD implantation for primary prevention between 2019 and 2022. All the participants satisfied the indication criteria (Class I or Class IIa) as outlined in the 2019 JCS/JHRS guidelines.³ The study was conducted according to the ethical guidelines of the Declaration of Helsinki. The study protocol was approved by the Medical Ethics Committee of Tosei General Hospital. Shock reduction programming, including a high-rate cutoff and prolonged detection duration, was applied in all patients in accordance with current consensus recommendations.⁴

Results

The mean age of the participants was 70.6±12.8 years; 9/25 (36%) had ischemic cardiomyopathy (ICM). The average LVEF was 28.5±5.3%, and 13 (52%) patients were classified as ICD Class I indication. Cardiac resynchronization therapy (CRT) was utilized in 12 (48%) patients, and 84% had a history of HF hospitalization. Medications included β-blockers (84%), angiotensin converting enzyme inhibitors (60%), angiotensin receptor-neprilysin inhibitors (ARNI [16%]), and sodium–glucose cotransporter 2 (SGLT2) inhibitors (20%) (Central Figure).

Over a mean follow-up of 52.6±14.3 months, NSVT occurred in 20 patients (80%), and its incidence was comparable between Class I and IIa indications. Sustained VT occurred in 2 patients (8%), and in both cases it was successfully terminated by antitachycardia pacing. HF hospitalization occurred in 2 patients (8%), and 2 (8%) died from non-arrhythmic causes. LVEF improved significantly from 28.5±5.3% to 41.6±12.2% at follow-up. Patients who received CRT, ARNI, or SGLT2 inhibitors had greater improvement in LVEF than those who received none (∆8.5% vs. ∆6.0%, P=0.002). Specifically, the LVEF improvement was more pronounced in patients with CRT-on (∆13.3%) and ARNI-on (∆16.6%).

Discussion

In this real-world analysis of Japanese patients who received ICD for primary prevention, a high incidence of NSVT was observed, even among patients with Class IIa indications. No patients experienced appropriate shock therapy or sudden death, and the overall prognosis was favorable. Substantial improvement in LVEF was noted, suggesting a role of CRT or optimized medical therapy in stabilizing arrhythmias and supporting functional recovery. The low use of ARNI and SGLT2 inhibitors at the time of device implantation likely reflects their recent introduction in Japan during the study period. In patients with borderline blood pressure, initiating these agents before device implantation was often difficult. Thus, the observed LVEF improvement in ARNI users may be influenced by this fact. In addition, the consistent findings across different indication classes and the absence of shocks imply that shock reduction programming, such as high-rate cutoff and prolonged detection duration, may have contributed in suppressing unnecessary interventions while maintaining patient safety.

Study Limitations

This was a single-center analysis with a limited sample size. We acknowledge that our study cannot provide a definitive assessment of the safety of the shock-reduction strategy.

Conclusions

No appropriate shocks or sudden cardiac deaths occurred despite frequent NSVT. Improved LVEF, especially in patients receiving CRT and ARNI, suggests that optimized ICD programming and concomitant HF therapy may have contributed to the favorable outcomes.

Disclosure and Funding

This report did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of Interest Statement

There are no conflicts of interest to declare.

Declarations

IRB Information: The present study was approved by the Institutional Review Board of Tosei General Hospital. Reference number: 784.

Informed Consent: All patients provided written informed consent for the ablation procedure and enrollment in the ablation registry.

Animal Studies: N/A.

Data Availability

The deidentified participant data will not be shared.

References

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