Wearable cardioverter defibrillator after cardiac surgery: Analysis of real‐life data from patients at transient risk of sudden cardiac death

Abstract Background Especially in the first 3 months after cardiac surgery, patients are at transient risk of sudden cardiac death (SCD). To close the gap between hospital discharge and the final implantable cardioverter‐defibrillator (ICD) decision, guidelines recommend temporarily using a wearable cardioverter‐defibrillator (WCD) to protect these patients from SCD. We investigated real‐life data on the safety, effectiveness, and compliance of the WCD in this population. Methods Data for analysis were collected via the Zoll Patient Management Network (ZPM) from patients who underwent cardiac surgery and who were discharged with a WCD between 2018 and 2021 at the Cardiac Surgery Center of the University of Erlangen in Germany. Results The majority of the 55 patients were male (90.9%) and underwent a coronary artery bypass graft (80.0%). The number of patients with left ventricular ejection fraction (LVEF) >35% increased from 9.1% at the beginning of WCD use to 58.2% at the end of WCD use. Six ventricular tachycardia (VT) episodes occurred in four patients. The WCD appropriately defibrillated two patients with VT episodes. There were no inadequate shocks and no fatalities during the observation time. WCD wearing compliance was high, with a median wear time of 23.3 h/day. Conclusion This retrospective analysis in a single cardiac surgery center confirms prior data on the safety and effectiveness of the WCD in patients in post‐surgery care in a real‐life setting. The WCD successfully protected patients from SCD during life‐threatening VT episodes. WCD wearing compliance was high.


| INTRODUC TI ON
Sudden cardiac arrest (SCA) is the sudden cessation of cardiac activity. If there is no spontaneous resolution restoring blood circulation, or if no rapid measures are taken, such as defibrillation, cardioversion, or resuscitation, SCA can lead within minutes to sudden cardiac death (SCD), which is defined as death due to cardiac causes within an hour of symptom onset (ACC/ AHA/HRS et al., 2006;Priori et al., 2001). In Germany, the SCD rate is approximately 81 cases/100,000 person/year, corresponding to 65,000 deaths per year (Martens et al., 2014). In 75-80% of the cases, life-threatening ventricular tachycardia/ventricular fibrillation (VT/VF) are identified as a cause of SCD (Bayés de Luna et al., 1989;Demirovic & Myerburg, 1994;Priori et al., 2001). Severely reduced left ventricular ejection fraction (LVEF) is the most important risk factor for SCD (Priori et al., 2001) and highly correlates to life-threatening VT/VF (Kutyifa et al., 2015). Cardiac surgery is recommended in patients with aortic valve stenosis and left ventricle (LV) dysfunction or significant ventricular arrhythmias (VA) even if they are asymptomatic (Priori et al., 2001) and can reduce the risk for SCD. Despite vast advances in surgery techniques, post-surgery mortality risk is high, especially in the first 3 months after the intervention, and often due to reduced LVEF and life-threatening VT/VF (Kaul et al., 1998;Rao et al., 2017).
The European Society of Cardiology (ESC) guideline for the diagnosis and treatment of acute and chronic heart failure recommends an implantable cardioverter-defibrillator (ICD) to reduce the risk for SCD for patients with ongoing reduced LVEF for 3 months or longer after diagnosis of heart failure and despite surgery and/ or guideline-directed medical treatment (McDonagh et al., 2021). To close the gap between hospital discharge and the final decision on ICD implantation, the ESC guideline for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death recommends since 2015 the use of a wearable cardioverterdefibrillator (WCD) to reduce the risk of SCD in this particularly vulnerable time (Priori et al., 2015).
A WCD is a vest with non-adhesive electrocardiography electrodes, which continuously monitor the patient's heart rhythm, and defibrillation electrodes, which are designed to automatically deliver a therapeutic shock in case of potentially fatal ventricular tachyarrhythmia (Deneke et al., 2019;Kutyifa et al., 2015). The safety and effectiveness of using WCD were confirmed in the randomized controlled trial "VEST" and several large real-world studies. The VEST trial showed a significant reduction of overall mortality in the intention-to-treat analysis (Olgin et al., 2018) and a significant reduction in mortality due to arrhythmia in the per-protocol and astreated analysis (Olgin et al., 2020).
Data on WCD use after cardiac surgery and after hospital discharge, until a final decision on the implantation of an ICD has been made, are limited.
The aim of this retrospective data analysis of a single cardiac surgery center in Germany was to collect clinical and demographic data on cardiac surgery patients, as well as to analyze the safety, effectiveness, and compliance of WCD use in a real-life setting.

| Study design and patient population
For this retrospective analysis, data from 55 patients who underwent cardiac surgery between 2018 and 2021 at the Cardiac Surgery Center of the University of Erlangen, Germany were included. These patients were at risk for sudden cardiac death (SCD) and were discharged with a wearable cardioverter-defibrillator (WCD, LifeVest® Wearable Cardioverter Defibrillator; ZOLL Pittsburgh, Pennsylvania, USA). According to the ethics committee of the Faculty of Medicine University of Erlangen, Erlangen, Germany, this retrospective analysis with fully anonymized patient data did not require a specific assessment by the ethics committee.

| Zoll patient management network (ZPM)
The WCD-integrated monitoring system documents and transfers all detected arrhythmias, as well as several other parameters, such as heart rate and rhythm, electrocardiography (ECG), and wear-time, to the Zoll Patient Management Network (ZPM). Based on this information, the treating physician can adjust therapy and medication as needed. The ZPM automatically processes and stores data.
For this retrospective data analysis, data from the ZPM, as well as data collected during clinical routine, were used. Components and detailed functionality of the WCD are described elsewhere (Klein et al., 2013).

| Data collection
Demographic characteristics, data on diagnosis, cardiac surgery, and hospital stay, as well as data on medication and cardiac arrhythmia pre-and post-surgery, were collected in routine clinical care. Moreover, LVEF was determined before surgery, at the beginning and end of WCD use. During WCD use, average wear time per day, the occurrence of arrhythmia and their treatment, post-shock rhythm as well as the reason for the end of WCD use were collected.

| Statistical analysis
The proportion of days when the WCD was worn (i.e., number of days actually wearing the WCD in relation to the number of days having the WCD), the time until the first episode with VT/VF after surgery as well as the first episode of VT/VF after the start of WCD use were calculated.
All data were analyzed descriptively. LVEF was analyzed as numeric and categorical variables (≤35% vs. >35%) at various time points (before hospital stay, at the beginning of WCD use, and at the end of WCD use). LVEF was also analyzed stratified by age (≤60 years vs. >60 years), sex, original diagnosis, and surgical procedure. Variables related to adherence (average wearing time per day, wear time in days, the proportion of days wearing the WCD) were analyzed stratified by age, sex, diagnosis, surgical procedure, LVEF before hospital stay (≤35% vs. >35%), and reason for the end of WCD use.
All analyses were performed using statistical software (SAS, version 9.4).

| Patient and clinical characteristics
In total, 55 patients, who received a WCD after cardiac surgery at discharge from the hospital, were included in this retrospective data analysis. Most of the patients were male (90.9%) with a median age of 60 years (IQR: 55-70 years) ( Table 1). A total of 44 patients (80%) underwent coronary artery bypass graft (4 [7.3%] in combination with heart valve intervention), and six patients (10.9%) had an ICD explantation mainly due to device infection. The median time in the hospital was 17 days (IQR: 13-24). 14.5% of the patients had a history of atrial fibrillation.
No deaths occurred during the use of a WCD.

| Left ventricular ejection fraction (LVEF)
Median LVEF before hospital stay and at start of WCD use was 25.0% (IQR before hospital stay: 20.0-35.0%; IQR at start of WCD use: 20.0-30.0%) and improved at the end of WCD use (median: 40.0%, IQR: 25.0-45.0%) (Figure 1a). The proportion of patients with LVEF >35% dropped from 21.8% before hospital stay to 9.1% after surgery/beginning of WCD use and increased to 58.2% at the end of WCD use (Figure 1b).
The percentage of patients with LVEF >35% for each time point by subgroups is given in Table 3. At each time point, the percentages of men and women with LVEF >35% were similar. While the percentage of patients with LVEF >35% before hospital stay and at the beginning of WCD use did not differ essentially between age groups, a higher percentage of patients ≤60 years of age (67.9%) showed LVEF >35% at the end of WCD therapy compared to older patients (48.1%). Because of the low number of patients in some of the subgroups, the results should be interpreted with caution.

| VT/VF episodes and treatment shocks during WCD use
During WCD use, only appropriate shocks (i.e., no superfluous or inappropriate shocks) were delivered. Ten patients (18.2%) experienced atrial fibrillation, and four patients (7.3%) experienced VT episodes (in total, 6 VT episodes). All initial VT episodes occurred within 3 months after surgery (range: 14-58 days). No treatment shocks were required for 4 VT episodes because of the following reasons: For two VT episodes, patients were conscious and pressed the response button to F I G U R E 1 Progress of LVEF.

TA B L E 3
Patients with LVEF >35% in subgroups.
prevent the shock; one episode was a non-sustainable VT (nsVT) (15 s), and one episode showed only two short ventricular salves. Two VT episodes warranted shocks and were adequately treated by the WCD. These two patients are described in detail in Table 4.
Both patients were male and underwent cardiac surgery without complications. Patient 1 underwent cardiac surgery because of Ebstein malformation, and patient 2 had an ICD explantation because of infection. Initially, ICD was implanted as secondary prophylaxis.
While patient 1 had LVEF >35% before surgery, at the beginning and at the end of WCD use, patient 2 had LVEF ≤35% at all time points.
After WCD use, patient 1 underwent an ICD implantation for the first time, and patient 2 underwent ICD re-implantation. Patient 1 experienced VT episodes 21 and 30 days after surgery, respectively.
Patient 2 experienced VT episodes 29 and 110 days after surgery, respectively. In both patients, WCD defibrillation was successful in re-establishing a sinus rhythm.

| WCD compliance
The general WCD wearing compliance was very satisfactory.
However, one patient refused to wear the WCD at all. For about half of the patients (50.9%), WCD use could be discontinued upon doctor's advice because of improvement of their LVEF (Table 5). For more than one-third of the patients (36.4%), WCD use was discontinued because an ICD implantation was performed. WCD use was terminated for five patients (9.1%) because of non-compliance.

| DISCUSS ION
In this retrospective analysis from a single cardiac surgery center in Germany, safety, effectiveness, and compliance of WCD use were investigated in patients after cardiac surgery in a real-life setting.
The presented data complement the study results of a recent, large German multi-center study reported by Kuehn et al. (2022) In post-surgical patients, the temporary use of WCD is particularly warranted in patients at high risk for SCD. In our study population, 50 (90.9%) patients had an LVEF ≤35% after surgery and were, therefore, by broad consensus, at high risk for SCD. A substantial number (n = 4, 7.3%) of the study patients experienced VT episodes while wearing the WCD. In these patients, as expected, the first VT episode occurred within 3 months (14-58 days) after surgery. In two patients (3.6%) the WCD registered a life-threatening VT warranting an intervention and successfully delivered a defibrillation shock in both cases. During the observational time, none of the WCD devices delivered inappropriate shocks. In four instances, shock delivery was not necessary, and VT episodes were, correctly, not treated. These findings on the effective delivery of shocks are in line with the recently published German multi-center study, which included 1168 patients using WCD after cardiac surgery (Kuehn et al., 2022) Therefore a prospective observational study was designed which should be completed in the next 5 years to address whether the patient's physical activity after the operation might influence the recovery of the myocardium.
To ensure high effectiveness, the continuous wearing of the WCD is one of the main requirements for effective protection from SCD (Olgin et al., 2020). In this real-life setting, WCD-wearing compliance of patients in post-surgery care with transient risk for SCD was very high, as the device was worn on almost all days (96%), with an average daily wearing time of more than 23 h. These findings are in accordance with previous studies on patients using a WCD (Kuehn et al., 2022;Nguyen et al., 2018).

| Strengths and limitations
A limitation of this study is the rather low number of patients from a single cardiac surgery center, making comparisons between subgroups difficult. However, our study still gives valuable insight into the efficacy of the WCD in a real-life setting. Moreover, our study supports the reported findings of a large German multi-center study (Kuehn et al., 2022).

| CON CLUS IONS
In conclusion, our retrospective analysis confirms the effectiveness and safety of the WCD in a real-life setting. It supports prior data on good patient compliance in spite of the specific situation of heart surgery patients, especially those after thoracotomy. We showed that the WCD successfully protected patients from SCD during lifethreatening VT episodes after cardiac surgery. The collected data support the high benefit of WCD use to increase patient safety after cardiac surgery.

AUTH O R CO NTR I B UTI O N S
The concept/design was done by M.B. and T.S., and critical revision

ACK N OWLED G M ENTS
The authors would like to thank GKM Gesellschaft für Therapieforschung mbH (Munich, Germany) for support in statistical analysis. Open Access funding enabled and organized by Projekt DEAL.

FU N D I N G I N FO R M ATI O N
The authors received no financial support for the research, authorship, and/or publication of this article.

CO N FLI C T O F I NTER E S T S TATEM ENT
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The raw data supporting the conclusions of this article will be made available by the authors without undue reservation to any qualified researcher.

E TH I C A L A PPROVA L
The Institutional Review Board was waived due to the retrospective nature of the study as well as the fully anatomized identity of the research subjects.