Background: According to current ESC guidelines the implantable subcutaneous defibrillator (S-ICD) should be recommended in primary and secondary prevention of sudden cardiac death if there is no need for cardiac pacing. However, the number of patients that will require pacing during follow-up is under debate.

Methods and results: Our large-scaled S-ICD registry (n=383 patients, follow-up duration up to 11 years) was screened for patients who had to switch the ICD system to a transvenous ICD because of need for pacing for symptomatic bradycardia. Of these patients, the S-ICD was implanted for prevention in 54% and for secondary prevention of sudden cardiac death in 46%. 76% had structural heart disease.

During follow-up only one patient who underwent resection of an atrial myxoma developed symptomatic sick sinus syndrome during follow-up and was therefore changed to a DDD-ICD. One further patient was admitted to the ICU after cardiac arrest despite having an S-ICD. ECG ad admission showed sinus bradycardia. The patient died on the ICU due to hypoxic brain damage, cause of cardiac arrest could not sufficiently be cleared. Additionally, there were suspect syncopes in 5 patients with an S-ICD without any ECG recordings and no arrhythmias in the S-ICD storage. In these patients implantable loop recorders were additionally implanted for bradycardia screening. However, there was no bradycardia detected by a loop recorder during follow-up.

Conclusion: In a large consecutive cohort of S-ICD patients symptomatic bradycardia is a very uncommon finding so that the need for future pacing may be overestimated . During long follow-up, documented bradycardia only led to one explantation of an S-ICD. Thus, there is need for better prediction of patients at real risk for bradycardia who may rather benefit from a transvenous ICD than a S-ICD.