Methods 
Study design
This study involved a retrospective analysis of data from seven patients who were admitted to our treatment center between December 2022 and January 2023 for ICD shock or ventricular arrhythmias after SARS-CoV-2 infection. All patients signed an informed consent form, and the study complied with the Declaration of Helsinki.
Data collection
The enrolled patients’ clinical data were collected and recorded, including primary data such as age and sex, device type and model, underlying disease, New York Heart Association (NYHA) cardiac function classification, and presence of comorbid diseases. Data related to device parameters and events, such as the ICD parameter settings, treatment type and frequency, arrhythmia type, and termination mode were also collected. Ancillary examination data were also obtained, including data from electrocardiograms and cardiac ultrasounds, as well as concentrations of electrolytes, markers of myocardial injury, and N-terminal pro-B-type natriuretic peptide (NT-proBNP).
Definitions related to ICD treatment of the study
Appropriate ICD treatment was defined as the correct treatment selection and delivery for persistent ventricular and hemodynamically unstable arrhythmias.
Inappropriate ICD treatment was defined as an inappropriate response to any signals other than those related to sustained ventricular and hemodynamically unstable arrhythmias.
The default event termination criteria of the ICDs were defined as eight consecutive intervals greater than or equal to the programmed diagnostic tachycardia circumference after antitachycardia pacing (ATP) or shock therapy.
The clinically recognized criteria for ICD treatment success were defined as the successful conversion of arrhythmia to sinus rhythm and its maintenance.
Ventricular electrical storm was defined as three or more sustained ventricular arrhythmic episodes occurring at least 5 min apart within a 24-h period, with each episode requiring termination by the intervention.13
Determination of the cause of inappropriate electroshock treatment
Following ICD treatment, two skilled deputy chief physicians with experience in electrophysiology ascertained the appropriateness of the electroshock treatment by examining the simulated body surface and intracavitary electrograms obtained through the program controls in conjunction with the patient’s clinical condition. If the two deputy chief physicians’ assessments were in disagreement, consensus was based on the chief physician’s assessment. This methodology was crucial for identifying the causes of any inappropriate electroshock treatments.
Results
The baseline characteristics of the patients are shown in Table 1. The mean age was 67±10 years (range: 51–78 years). Six patients were male and one was female patient. Six of the seven patients had an ICD implanted for the treatment of ischemic cardiomyopathy; the other had an ICD implanted for the treatment of long QT syndrome. Two patients had implanted CRT-Ds (Medtronic, DTBC2QQ), whereas the remaining five had ICDs (Medtronic, BVAC). Four patients received ICDs for primary prevention for the treatment of ischemic cardiomyopathy with a low left ventricular ejection fraction (LVEF). One patient received ICDs for the secondary prevention of long QT syndrome with frequent torsades de pointes. Two patients received ICDs for the secondary prevention of ischemic cardiomyopathy with VT. The mean time since device implantation was 40±18 months.
The patient implant device settings are shown in Table 2. In one patient with atrial fibrillation (AF) at the time of implantation, the VF diagnostic interval was set to 270 ms to avoid inappropriate shock of the CRT-D due to AF, with as rapid a ventricular rate as possible. In another patient, the VT diagnostic interval was set to 390 ms based on the ventricular rate measured during previous VT episodes to optimize the device’s ability to recognize VT as much as possible and provide treatment as early as possible to terminate the event.
The types of arrhythmias and the characteristics of the treatments administered by the devices for each of the seven patients are shown in Table 3. In seven patients, the average time between the initial onset of symptoms of COVID-19 infection and device shock was 9±5 days (range: 3–20 days). The average QT interval was 460±46 ms (range: 386–536 ms) in the seven patients; however, six patients exhibited QT intervals exceeding 440 ms. Five patients exhibited a significant prolongation of the QT interval after COVID-19 infection compared with the QT interval measured at the time of device implantation.
Review of the program control data from the patients’ records revealed that seven patients received a combined total of 54 ATP treatments, all of which satisfied the default ICD criteria for event termination, including one case that fulfilled the clinically determined criteria for successful treatment. Additionally, four patients briefly exhibited evidence of sinus rhythm recovery following ATP treatment, with the event ultimately terminated by shock delivery. Another patient with a low ventricular rate during a VT episode resulting from long-term β-blocker use did not undergo ATP treatment or receive a shock; that patient was placed on a programmed ICD for in vivodefibrillation, which briefly restored the rhythm before recurrence, with the VT episode eventually being terminated via external defibrillation (see Case 2 for details). In total, the seven patients experienced 80 ICD shocks post-infection, 71 (88.75%) of which were administered for VT and nine (11.25%) of which were administered for AF; overall, this resulted in 66 successful terminations of arrhythmic events (82.5% effective). In total, ATP therapy was administered 54 times, resulting in the successful termination of 48 of these arrhythmic events. Five of the seven patients received appropriate treatment; two patients received inappropriate treatment. Three of the seven patients experienced ventricular electrical storms, with a single patient receiving shocks and ATP treatment with the greatest frequency (at 53 and 35, respectively; see Case 1 for details). The remaining four patients did not meet the diagnostic criteria for ventricular electrical storms, although they did receive shocks or ATP treatment multiple times within a single day.
The laboratory examination results are presented in Table 4. All patients exhibited symptoms of SARS-CoV-2 infection and tested positive for nucleic acids before admission. All patients demonstrated leukocyte and creatinine levels either within the normal range or only slightly elevated; with the exception of Case 2, who exhibited significantly elevated levels of both leukocytes and creatinine. Seven patients presented with varying degrees of electrolyte imbalance, which was primarily characterized by low blood concentrations of potassium and calcium. Six patients exhibited potassium levels below 4.0 mmol/L (range: 3.5–3.9 mmol/L), and five of the seven patients had blood calcium levels lower than 2.11 mmol/L. Troponin levels were elevated in five of the seven patients (range: 0.023–0.297 ng/mL). Additionally, all patients exhibited significantly elevated NT-proBNP concentrations at the time of admission (range: 608.8–25,758 pg/mL). The characteristics of two cases are described in more detail.
Case 1:  A 78-year-old male with ischemic cardiomyopathy underwent CRT-D implantation for primary prevention four years previously. One week prior, he became infected with SARS-CoV-2 and was referred to our institution due to experiencing recurrent shocks from the device. Upon admission, the program control data revealed recurrent VT, with 35 and 53 episodes of ATP treatment and shock, respectively. His blood pressure and heart rate were unstable, with a maximum heart rate of 202 beats/min. The program control data revealed that each ATP treatment could terminate the tachycardia; however, sinus rhythm could not be maintained continuously. While monitored by an external defibrillator, his device underwent programming to augment the number of ATP treatments and abbreviate the VF diagnostic interval to mitigate shock administration. After ATP treatment, the patient received intravenous antiarrhythmic medications, including amiodarone, lidocaine, and esmolol. His blood pressure returned to normal after one day and remained stable.
Case 2:  A 55-year-old male with ischemic cardiomyopathy and paroxysmal VT received an ICD for secondary prevention three years ago. The patient became infected with SARS-CoV-2 11 days before presentation and developed fever, palpitations, and muscle weakness. Two days before presentation, these symptoms worsened and were accompanied by dyspnea and an inability to lie down; therefore, he visited our institution. Upon admission, his physical condition was characterized by a temperature of 36.0 ℃, blood pressure of 81/67 mmHg, and oxygen saturation of 85% in a non-oxygenated state, with wet rales in both lungs. The program suggested that he was experiencing sustained VT, with a heart rate fluctuating between 145 and 157 beats/min. No ATP or shock therapy was administered because the ventricular rate had not entered the VT/VF diagnostic interval of the program. He was administered intravenous amiodarone and received active anti-heart failure (HF) treatment. Arterial blood gas analysis indicated metabolic acidosis and type I respiratory failure, and chest computed tomography indicated diffuse, exudative lung changes, suggesting the possibility of viral pneumonia. He received ventilator-assisted respiration, antiviral drugs, antibiotic treatment with meropenem, and anti-inflammatory treatment with methylprednisolone. However, his condition did not improve, multiorgan failure developed, and he died eight days after admission.