Implantable Cardioverter-Defibrillator of Korean Patients in a Single Center Registry

Background and Objectives: The safety and efficacy of implantable cardioverter-defibrillator (ICD) for Korean is unclear. We investigated the clinical characteristics and outcomes of Korean patients undergoing ICD for primary or secondary prevention. Materials and Methods: From October 1999 to December 2016, 396 cases (365 patients) of ICD implantation were performed: Baseline characteristics, procedural findings, and clinical outcome data were collected retrospectively from our ICD registry. The primary outcome was composite of cardiac death, appropriate shock or antitachycardia pacing. Results: Among 365 patients, 91 patients (25.9%) had ICD for primary prevention and 274 patients (75.1%) were for secondary prevention (51.2±17.10 years, male was 80.8%). The median follow-up period was 3.1 years (interquartile range: 1.6–6.0 days). The most prevalent etiology was dilated cardiomyopathy (46.2%) in the primary prevention and idiopathic ventricular tachycardia or fibrillation (24.4%) in the secondary prevention. The primary outcome was noted in 28.6% of the primary prevention and 33.2% of the secondary prevention (P=0.44). The rate of cardiac death was 2.2% in the primary prevention and 1.8% in the secondary prevention (P=1.00). The hospitalization due to heart failure was higher in the primary prevention compared with the secondary prevention (23.1% versus 13.5%, P=0.03). ICD therapy occurred in 134 patients (36.7%). Among them, 60 patients (44.8% of ICD therapy) experienced inappropriate shock. The most common cause of inappropriate shock was atrial fibrillation of flutter (AF/AFL). Conclusion: The clinical efficacy and safety of ICD in Korean is consistent with the data from Western countries.


Introduction
Annually, 500,000 people experience sudden cardiac death (SCD) in the USA. 1 Since the first implantation of implantable cardioverter-defibrillator (ICD) in 1980, cardiac care in high-risk patients with potentially life-threatening arrhythmias has significantly changed. Large-scale clinical trials clearly demonstrated that the ICD increases survival rates in selected patients, with a 30% to 50% reduction in mortality risk. [2][3][4] In these randomized controlled studies, the efficacy of ICD for the primary prevention of SCD has been established. An observational study has also reported similar results for primary prevention that were observed in randomized controlled trials. 5 Although research on the efficacy of ICD for secondary prevention is limited, recent guidelines recommend consideration of an ICD implantation for either primary or secondary prevention in selected patients. 6,7 For this reason, ICD implantation is widely performed in developed countries despite its high cost. Studies conducted to date have involved mostly Westerners, with only a few Asians being included.
In Korea, ICD has been available since the 1990s. Although the safety and efficacy of ICDs have been substantiated in patients from Western countries, only a few studies have proven its safety and efficacy in Korean patients. 8,9 Therefore, we retrospectively reviewed the experience of patients with ICDs in our center and evaluated the clinical efficacy of ICD implantation in Korean patients.

Study population
From October 1999 to December 2016, ICD implantation was performed in 396 cases (365 patients) in Samsung Medical Center, Seoul, Korea ( Figure 1). The initial implantation of ICD system was performed in 357 cases (357 patients). Generator change for elective replacement interval was performed in 28 cases, 22 of whom were initially implanted with ICD in our center, 2 experienced generator change twice, and 4 were implanted with ICD in another center. Lead reposition immediately after initial implantation was performed in 3 cases. Reimplantation of ICD system was also performed in 3 cases because of ICD system infection. Either lead or generator was changed in 2 cases for Riata lead recall, 2 cases for lead fracture, and 1 case for generator recall. All procedures were performed using standard techniques. All decisions about ICD implantation were based on contemporary guidelines. 6,7 Baseline characteristics, procedural findings, and clinical outcome data were collected retrospectively from the medical records in our ICD registry by research coordinators. All procedures were performed in accordance with the institutional guidelines of Samsung Medical Center, and all patients waived their written informed consent.

ICD devices and programming
All commercially available devices approved by the Korea Food & Drug Administration were implanted. The use of singlechamber or dual-chamber and single-coil or dual-coil ICDs depended on the preference of physicians. The ICD programming, including discriminator usage, also depended on the discretion of physicians. The therapy zone was divided into three zones (VF zone, VT2 zone, and VT1 zone), and the total number of zones where ICD therapy was set was counted for categorization.

ICD therapy event analysis
The ICDs were interrogated every 3-4 months after

Definition of clinical events
The primary outcome was defined as a composite of cardiac

Demographic and clinical characteristics
A total of 365 patients with ICD for primary or secondary prevention were analyzed in the study. The patient's baseline characteristics were categorized based on the intention of ICD implantation. Table 1

Clinical outcomes
The median follow-up period was 3.1 years (interquartile range: 1.6-6.0 years). The outcome data were compared based on the baseline etiology of heart failure and purpose of ICD implantation. The results were described in Table 3. The primary outcome was noted in 28.6% and 33.2% of patients with ICD for primary and secondary prevention, respectively (p=0.44). The survival rate from the primary outcome was not significantly different between these patients (log-rank p=0.87, Figure 3).
Among the patients with ICD for primary prevention, 2 patients (2.2%) died because of cardiac nonischemic cause. In contrast, among patients with ICD for secondary prevention, cardiac death was noted in 5 patients (1.8%, 3 and 2 because of nonischemic and ischemic causes, respectively). The survival rate from cardiac death was not significantly different between patients with ICD for primary and secondary prevention with respect to purpose and etiology ( Figure 4A). The rate of hospitalization because of heart failure was higher in patients with ICD for primary prevention than in those for secondary prevention (23.1% versus 13.5%, p=0.03). Hospitalization because of heart failure was more prevalent in the ischemic group than in the nonischemic group with ICD for secondary prevention (10.5% versus 23.0%, p=0.01). The hospitalization-free survival rate was significantly higher in the nonischemic group with ICD for secondary prevention than in other groups (log-rank p=0.01, Figure 4B).
Heart transplantation was performed in 7.7% and 4.7% of patients with ICD for primary and secondary prevention, respectively.  Values are mean ± standard deviation or n (%). ATP, anti-tachycardia pacing; VT, ventricular tachycardia; VF, ventricular fibrillation  Table 4 shows the independent risk factors to predict the Characteristics and Outcomes of Korean Patients Undergoing of Implantable Cardioverter-Defibrillator p=0.02) were consistently associated with an increased risk of primary outcome.

Discussion
The major findings of the study were that dilated CMP and idiopathic VT/VF were the most common etiologies for ICD implantation for primary and secondary prevention, respectively, and that coronary artery disease was the second most common.
The implantation rate was much higher in men than in women. The increasing pattern in the ICD implantation procedures over a 17-year study period is similar to that in other studies in the same periods. 12,13 However, the increasing rate of annual implantation is smaller than that in other studies probably because of different conditions of countries such as insurance regulations. In this study, the implantation rate in men was much higher than in women, and the finding is consistent with overserved in the USA and Europe. [13][14][15] Several factors are found to produce sex difference in the use of ICD. Curtis et al. analyzed the reason in their study and suggested that, at the presentation of disease, women tend to be older than men and the physicians have been less likely to recommend ICD implantation. 14 According to current guidelines, ICD therapy is recommended Characteristics and Outcomes of Korean Patients Undergoing of Implantable Cardioverter-Defibrillator in the patients expected survival more than 1 year with good functional status. 6,7 Our study showed that the ICD implantation rate was the highest in the 50s, which may explain why most patients are male.
The beneficial effects of ICD therapy have been well established in primary and secondary prevention. 3 According to the data of Daubert et al., more aggressive use of the available SVT discriminators could reduce the incidence of inappropriate therapy. 19 However, the information about stability or sudden onset was not available in our registry, and we could not analyze their effect. Dual-chamber ICD systems are commonly used to reduce the inappropriate therapy. The Detect Supraventricular Tachycardia Study reported a reduction of inappropriate detection in the dual-chamber system (30.9%) compared with that of the single-chamber system (39.5%).
However, several conflicting studies exist about the benefit of dual-chamber system. 21,22 In our study, 10.8% of patients with the dual-chamber ICD system experienced inappropriate shock, and the incidence was not significantly reduced compared with that of the single-chamber system (17.1%).

Study limitations
This study has several limitations. First, all parameters were based on the initial setting. As the patient's condition changed or many patients experienced ICD shock events, the parameters related to ICD therapy were changed in some patients. The changes of the ICD parameters could not be analyzed in a timedependent fashion. Second, the electrocardiogram interpretation to decide the suitability of the therapy was based on only available data. In some patients, missing electrocardiogram could not be confirmed the arrhythmia triggered therapy. Third, some unrecorded data on the registry could not be analyzed. For example, we could not get the data for stability and sudden-onset programming on the electronic medical record in a significant number of patients.

Conclusion
The most common etiologies for ICD implantation were dilated CMP and idiopathic VT/VF in patients with ICD for primary and secondary prevention, respectively. Inappropriate shocks were caused most commonly by AF/AFL.