In this interview we speak with Dr. Rodrigo Nehgme, electrophysiologist at the Arnold Palmer Hospital for Children in Orlando, Florida, about his first pediatric implantation case of a subcutaneous defibrillator.
What can you tell us about this first particular case? What were the reasons for the implant?
The patient is a 10-year-old boy with a history of syncope triggered by exertion. The events were characterized by the sudden onset of loss of consciousness and postural tone, followed at times by hypertonia and incontinence. On the last event prior to his hospitalization, his father who is a certified BLS provider, documented absence of palpable pulses and no breathing efforts with cyanosis and hypertonia. He gave a couple of rescue breaths and initiated chest compressions. The patient regained pulses and consciousness within two minutes. Neurological evaluation, including physical examination, EEGs, and brain CT and MRI, was normal. His cardiac evaluation demonstrated normal physical examination and baseline 12-lead ECG. Echocardiography confirmed normal cardiac anatomy and function. The origins of the right and left coronary arteries were normal. Exercise stress testing demonstrated normal heart rate and blood pressure responses to exercise, but frequent polymorphic premature ventricular contractions in couplets and triplets with a short coupling interval were seen (Figure 1). Epinephrine challenge test was negative for long QT syndrome. Electrophysiology study showed normal cardiac intervals, and atrial or ventricular arrhythmias were not inducible by programmed stimulation at baseline or under isoproterenol infusion. Genetic testing for hereditary cardiac muscle ion channel anomalies (channelopathies) was not performed.
He has moderate persistent asthma treated with Advair and albuterol. He also has insulin-dependent diabetes, which is well controlled on an insulin pump. His family history is negative for syncope, seizures, or sudden cardiac death in the young.
In summary, we had a young patient with a history of syncope with exertion, a resuscitated sudden death event (SCD), and polymorphic ventricular arrhythmia during exercise stress testing. His syncope and aborted SCD is the result of a channelopathy, most likely catecholaminergic polymorphic ventricular tachycardia (CPVT). Therapy with beta-blocking agents and in some cases flecainide, helps prevent episodes of VT in these patients. However, he also met guidelines criteria for implantation of a defibrillator because of his presentation with an aborted SCD event.
Because of his age and size at 46 kg and 153 cm, his diabetes, and the possible associated complications of implanting a transvenous ICD in his case, we thought he would benefit from a subcutaneous ICD (Figure 2), the S-ICD™ System from Boston Scientific.
When did the procedure take place? How is the patient doing today?
The procedure was performed in early April 2014 in the pediatric electrophysiology laboratory at Arnold Palmer Hospital using the standard technique, without complications (Figure 3). He was discharged home on post-operative day 1. The device was programmed to treat ventricular tachycardia/fibrillation with a Shock (80 J) Zone-240 bpm and Conditional Zone-200 bpm, Gain Setting-1X, Sensing Configuration-Primary, and Post Shock Pacing-ON. He was also started on the cardioselective beta blocker atenolol at 25 mg/day. We elected not to use propranolol or nadolol, non-selective beta blockers, because of his asthma and concerns related to the use of beta blockers in insulin-dependent diabetic patients.
He has recovered well post-op, and his incisions have healed well.
Last week, three months after implantation of the S-ICD System, he received an ICD shock for treatment of polymorphic VT (Figure 4). He felt dizzy while playing at the pool and then felt the shock, which he described as a sudden pain on his chest. Device interrogation confirmed an episode of polymorphic VT that was successfully terminated and converted to sinus rhythm with a single 80-Joule shock. The device probably saved his life. We changed his medication therapy by adding flecainide to his beta blocker, and scheduled him for an exercise stress test for further medication adjustments.
Have you implanted the subcutaneous ICD in more pediatric patients since this case?
No. We recently had a similar case of a 9-year-old girl who was resuscitated after a near drowning event at her pool at home. Her workup was diagnostic of long QT syndrome and torsades de pointes ventricular tachycardia. However, she was smaller (32 kg and 131 cm) and thin, with inadequate subcutaneous tissue to safely create a pocket for the subcutaneous ICD, which is larger at 70 cc than a small transvenous ICD at 26 cc.
Is the subcutaneous ICD currently being used in adult patients at other Orlando Health hospitals as well?
Yes. I understand the internal medicine electrophysiologists have implanted a few devices in adult patients at Orlando Regional Medical Center.
Why is the subcutaneous ICD a good option for pediatric patients? What have complication rates been like?
ICD therapy reduces the risk of sudden death in patients at high risk of developing ventricular arrhythmias. Conventional ICD systems use a transvenous lead for pacing, sensing and delivery of electrical therapy. Subcutaneous ICD systems use a subcutaneous lead for sensing and delivery of ICD therapy. Both use the can of the pulse generator as the other defibrillation pole. The implantation of both systems is associated with risks such as pocket hematoma and infection, and lead displacement or dislodgement. Placement of transvenous leads carries additional complications including pneumothorax, vascular damage, hemothorax, tricuspid valve damage, cardiac perforation, pericardial effusion, tamponade, embolism, venous thrombosis, systemic infection, and endocarditis. In children, continuing growth, active lifestyle, and longer life expectancy when compared to their adult counterparts pose additional challenges for endocardial leads. Children will normally outlive their leads, and therefore, they will be exposed to considerable morbidity and even mortality from transvenous lead-related complications. Thus, an entirely subcutaneous system is desirable in young patients, since the lack of intravascular elements in the S-ICD System will help avoid those complications.
Are there any patients who are not suitable for the subcutaneous ICD?
Yes. The S-ICD System does not provide atrial or ventricular pacing for the treatment of bradycardia. Patients who require pacing therapy for bradycardia or ventricular resynchronization (CRT) will benefit from a capable device using transvenous or epicardial pacing leads. Thus, the subcutaneous ICD is not suitable when bradycardia pacing is indicated, when CRT is indicated, or when VT can be reliably terminated with anti-tachycardia pacing. Other patients not suitable for the S-ICD System are those with unipolar pacing implants and epicardial defibrillation patches. Patients with incessant VT are not good candidates for ICD therapy. The S-ICD generator is also a large device that may not be suitable for small pediatric patients in its current generation, because of technical implantation issues and concerns of erosion over time. As technology evolves, we hope the S-ICD devices will become even smaller.
How long is the battery life of the subcutaneous ICD compared with a traditional ICD?
Battery life depends on usage. The S-ICD System’s estimated longevity with normal use is five years. Normal use is defined as three full-energy device capacitor charges, with or without shock delivery, per year. Transvenous ICD longevity is approximately twice as long.
Is there a difference in procedure time when implanting the subcutaneous ICD?
I expect the procedure implant times to be similar for the transvenous ICD and S-ICD Systems.
Has the subcutaneous ICD been evaluated for pediatric use?
No, the S-ICD System has not been evaluated for pediatric use. There are anecdotal reports of pediatric patients receiving the S-ICD System. The trials have primarily included patients older than 18 years. The lack of experience or trial evaluation is not unusual in pediatric cardiology because of the small number of children requiring this type of therapy.
Why was it important for Arnold Palmer Hospital to offer this technology as an option for pediatric patients?
The S-ICD System is a new technology that has advantages for certain pediatric patients who require lifelong ICD therapy as previously explained. We believe we should offer our pediatric patients the best possible available therapy, as well as technological and technical advances to improve their health and quality of life.
Disclosure: Dr. Nehgme has no conflicts of interest to report regarding the article herein.