Author + information
- Louise R.A. Olde Nordkamp, MD, PhD∗ (, )
- Giulio Conte, MD, PhD,
- Boudewijn R.A.M. Rosenmöller, MSc,
- Joppe L.F. Warnaars, MD,
- Hanno L. Tan, MD, PhD,
- Maria L. Caputo, MD,
- Francois Regoli, MD, PhD,
- Tiziano Moccetti, MD,
- Angelo Auricchio, MD, PhD,
- Reinoud E. Knops, MD and
- Arthur A.M. Wilde, MD, PhD
- ↵∗Department of Cardiology, Academic Medical Center, PO Box 22700, 1100 DE Amsterdam, the Netherlands
The subcutaneous implantable cardioverter-defibrillator (S-ICD) avoids important periprocedural and long-term complications associated with transvenous leads of the conventional ICD (1). This may be particularly beneficial for younger patients with inherited arrhythmia syndromes who do not need pacing therapy, such as patients with Brugada syndrome (BrS).
Sensing the heart rhythm is different in the S-ICD compared with the transvenous ICD. The arrhythmia discrimination algorithm is based on a comparison between a template acquired after the implantation and a spontaneously occurring supraventricular or ventricular arrhythmia (2). This morphology-based sensing is susceptible to QRS-/T-wave oversensing, which is the leading cause of inappropriate shocks by the S-ICD (3). Sensing might be particularly difficult in BrS patients because of the dynamic nature of the electrocardiographic (ECG) morphology. Over time and during fever, the ECG of BrS patients may change from a type 3 or 2 Brugada ECG to type 1 Brugada ECG (BrS-ECG). Type 1 BrS-ECG, which is characterized by prominent ST-T segment changes, is particularly relevant because it is strongly linked to the occurrence of arrhythmias. We therefore studied whether BrS patients with a type 1 ECG are suitable for an S-ICD.
In consecutive patients who underwent ajmaline testing to screen them for BrS (provocation of type 1 BrS-ECG) at 2 European centers (AMC [Academic Medical Center]: n = 77; CCT [CardioCentro Ticino]: n = 11), we performed QRS-/T-wave morphology analysis before and during ajmaline infusion. We used an ECG simulating the 3 sense vectors of the S-ICD (Boston Scientific, Marlborough, Massachusetts), as recommended by the S-ICD manufacturer to screen for S-ICD suitability (2). Morphology analysis was defined as appropriate when ≥1 sense vector was acceptable in both supine and standing positions.
Eighty-eight patients (mean age 49 ± 14 years; 41 men [47%]) underwent ajmaline testing, including 19 (22%) with symptoms such as syncope or a history of ventricular fibrillation. At baseline, 67 patients (76%) had a normal ECG, 17 (19%) had a type 3 BrS-ECG, and 4 (5%) had a type 2 BrS-ECG. Eighty-six patients (98%) had appropriate morphology analysis at baseline. The 2 patients who had the morphology analysis fail had a type 3 BrS-ECG and a normal ECG at baseline, respectively.
Ajmaline testing evoked type 1 BrS-ECGs in 21 patients (24%; 6 men [29%]; mean age 55 ± 13 years). All 21 patients had appropriate morphology analysis at baseline. However, during type 1 BrS-ECG, 5 patients (24%; 4 women) had inappropriate morphology analysis and were therefore deemed not suitable for S-ICD implantation. In all patients, the reason for inappropriateness was the more pronounced T-wave during type 1 BrS-ECG (Figure 1). Moreover the primary, secondary, and alternate vectors were generally less often appropriate during the development of a type 1 BrS-ECG, with the primary sensing vector being appropriate in 18 of 21 patients at baseline and in 15 of 21 patients during type 1 BrS-ECG. The secondary sensing vector was appropriate in 19 of 21 patients at baseline and in 11 of 21 patients during type 1 BrS-ECG, and the alternate vector was appropriate in 11 of 21 patients at baseline and in 4 of 21 patients during type 1 BrS-ECG. With fewer sense vectors deemed appropriate during the development of type 1 BrS-ECG, optional vector selection during implantation or after inappropriate shocks may be hampered.
This study demonstrates that sensing of the S-ICD can change from appropriate to inappropriate during a changed ECG signal, such as development of type 1 BrS-ECG. Although the sample size may be considered small, the finding was consistent in 2 different centers. The static detection and morphology analysis can be mitigated by the development of an algorithm capable of dynamic analysis of simultaneous multiple vectors.
This is the largest report on potentially inappropriate sensing by the S-ICD in patients with BrS. The morphology analysis failed in 24% of patients upon development of type 1 BrS-ECG during ajmaline testing, although morphology analysis in these patients was appropriate at baseline. These patients are accordingly at risk for inappropriate shocks. We therefore recommend that in the presence of a type-1 Brs-ECG after S-ICD implantation, for example, during fever or during an additional ajmaline test, all 3 sensing vectors should be evaluated, and the best suitable sensing vector should be programmed. We determine suitability on the basis of the presence of QRS- or T-wave oversensing, and if absent, on the basis of the most optimal R-wave/T-wave ratio based on visualization. Hence, critical analysis is necessary to ensure appropriate sensing and to prevent inappropriate sensing in BrS patients with an S-ICD.
Please note: Dr. Regoli has received speaker’s fees from Medtronic and LivaNova. Dr. Auricchio has been a consultant to Medtronic, Boston Scientific, LivaNova, and St. Jude; and has received speaker’s fees from Medtronic, Boston Scientific, and LivaNova. Dr. Knops has received a research grant from Boston Scientific. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation
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- ↵Cameron Health. SQ-RXTM Pulse Generator. A Component of the S-ICD System. User's Manual. Model 1010. 2009.