The subcutaneous implantable cardioverter defibrillator (S-ICD) has become an alternative
to the transvenous ICD in indicated patients. However, inappropriate shock or failed
ventricular tachycardia/fibrillation conversion is the most alarming complication
of S-ICD. Therefore, defibrillation test (DFT) is recommended for the S-ICD implantation.
However, the DFT can provoke or worsen cardiac arrhythmias. We present two induced
atrial fibrillation (AF) cases by DC bursts on DFT during S-ICD implantation. The
AF was not terminated by the 65-J S-ICD shock, even when ventricular fibrillation
Case 1. A 49-year-old female patient was transferred to our emergency room with sudden
collapse due to the ventricular fibrillation (VF). After DC cardioversion by the emergency
medical team on the spot, her rhythm was recovered. There was no reversible cause
for her VF, and implantation of the S-ICD was planned. The device was an EMBLEMTM
MRI S-ICD (Boston Scientific, Marlborough, MA, United States). The ICD implantation
was performed under conscious sedation with local anesthesia. Two incisions were made
at the midaxillary and subxiphoid areas respectively, and the pulse generator was
placed into the intermuscular space on the left midaxillary line between ribs five
and six. The subcutaneous lead was placed parallel to the left of the sternum, targeting
near the sternal notch.[1, 2] Standardized DFT was performed by delivery via the programmer.
The first shock energy was set to 65-J, the second shock energy was set to 80-J, followed
by an external rescue shock to 360-J if ineffective. The sensing vector (primary,
secondary, or alternate) was automatically selected by the device and 50-Hz, 200-mA
DC bursts for four to six seconds were used for the induction of VF. The first induced
VF was spontaneously terminated; however, the AF was induced and persisted after the
DC bursts (Figure 1). The second VF induction showed the same pattern of non-sustained
VF and the AF was still ongoing, which was spontaneously terminated in two minutes.
The third instance of DC bursts for four seconds finally induced sustained VF, which
was successfully terminated by 65-J of the S-ICD shock. However, the AF was again
induced and sustained after the shock and spontaneously terminated ten minutes later
(Figure 2). The implantation procedures were completed without further complications.
After recovering the sinus rhythm, the AF was no longer observed until the discharge
of the patient.
Non-sustained VF was induced by 50-Hz DC bursts.
After the spontaneous termination of the VF, the atrial fibrillation was induced and
persisted. VF: ventricular fibrillation.
DC bursts for four seconds induced sustained ventricular fibrillation, which was successfully
terminated by 65-J of the S-ICD shock.
However, atrial fibrillation was induced and sustained after the shock.
Case 2. A 46-year-old woman was delivered to our emergency room with sudden collapse
due to the VF. Before her collapse, she had consumed two bottles of alcohol. After
DC cardioversion by the emergency medical team on the spot, her rhythm was recovered.
She had no history of any illness or medication. Her initial electrocardiogram after
DC version was normal sinus rhythm. Echocardiography showed normal heart function
and ergonovine provocation coronary angiogram showed negative findings. Consequently,
the implantation of S-ICD was planned. The S-ICD was the same product and the implantation
procedure was identical to that in Case 1. Standardized DFT was performed and the
shock setting and induction method were the same as those in Case 1. The sensing vector
was automatically selected by the device and 50-Hz, 200-mA DC bursts for four seconds
were used for the induction of VF. However, the AF was induced instead of VF (Figure
3). Notably, the AF was terminated spontaneously within a short period of time. Subsequently,
the VF induction was successful and the VF was successfully terminated by the first
65-J of the S-ICD shock. The implantation procedures were completed without further
complications and the AF was not observed after DFT.
DC bursts for four seconds were attempted for the induction of VF.
However, the atrial fibrillation was induced instead of VF. VF: ventricular fibrillation.
The S-ICD has become an alternative to the transvenous ICD in indicated patients.
However, the S-ICD can also cause several complications. Among them, inappropriate
shock due to oversensing or failed ventricular tachycardia/fibrillation conversion
is the most critical complication of S-ICD. As the subcutaneously positioned electrodes
are widely spaced and are placed at greater distances from the ventricle, a higher
amount of energy is required for the successful termination of arrhythmias.[1, 3]
Therefore, the DFT is recommended as a class I indication for assessing arrhythmia
detection and termination for the S-ICD implantation.[3-6] However, the DFT itself
or cardioversion shock has the capacity to provoke or worsen cardiac arrhythmias.
The majority of the reported episodes are transient; however, they may be sustained
in patients with the substrate to support AF or atrial flutter and induced AF with
a rapid ventricular response may cause several serious situations. In addition,
supraventricular tachycardias (SVT) are complicated in 6% of external cardioversions
for ventricular tachyarrhythmia. Judging from these results, SVT, especially the
AF could be complicated by the DFT during the S-ICD implantation. To the best of our
knowledge, there is no report of induced AF during the DFT on S-ICD implantation.
In our center, two cases of induced AF were observed by DC bursts on S-ICD implantation.
The AF in Case 1 was not terminated by the 65-J S-ICD shock, even when the VF was
terminated. Further research and case reports about induced AF or SVT burden, adequate
management, and prognosis during the DFT on S-ICD implantation will be required.
All authors had no conflicts of interest to disclose.