Much like the traditional implantable cardioverter defibrillators (ICDs), subcutaneous implantable cardioverter defibrillators (S-ICDs) are used to treat patients who have experienced or are at risk for ventricular tachycardia and ventricular fibrillation (life-threatening heart arrhythmias). These devices continuously monitor the heartbeat and automatically deliver a small electrical shock to the heart to convert a potentially lethal rhythm into one that will sustain life.
Unlike the transvenous ICDs, which utilize wire leads inserted directly into the heart through a large vein, the S-ICD system uses a subcutaneous (beneath the skin) electrode that rests near (but not in) the heart to both sense lethal heart arrhythmias and deliver therapy. The electric pulse generator is implanted just below the armpit.
How is the ICD Implanted?
- The implantation requires the patient to have general anesthesia but not X-ray fluoroscopy.
- The device’s pulse generator is placed right below the left armpit using a 4- to 5-inch incision.
- An electrode attached to the device is tunneled across the ribcage above the heart and is anchored in place under the skin.
The S-ICD is tested while the patient remains under general anesthesia.
Benefits of the S-ICD
- The electrode that delivers the shock is placed near but not directly into the heart. This reduces the chance of infections.
- The design of this system allows for energy to be delivered (through the electrode) to the heart without the electrode having to touch the heart or its neighboring vessels.
- The device’s electrocardiogram (mechanism that monitors heart arrhythmias) is potentially better at detecting shockable arrhythmias (ventricular tachycardia and ventricular fibrillation) and less likely to discharge in the event of a non-life threatening arrhythmia such as atrial fibrillation.
- The placement of the pulse generator under the armpit reduces visible incision scarring.
Who is a candidate for the Device?
The S-ICD device, which is about the size of a large box of raisins, is about twice as large as a traditional ICD, which makes some patients—especially those who are very thin— potentially ineligible. In addition, because the detection algorithm uses a virtual surface electrocardiogram, a small percentage of patients may not qualify for the device due to T wave oversensing. The S-ICD also does not have standard pacing support or the ability to deliver antitachycardia pacing, so it would not be offered to patients with symptomatic bradycardia or who have slow ventricular tachycardia.
Patients receive detailed follow-up instructions before leaving the hospital. Adhering to these instructions is important and patients should call their doctor or nurse with any questions.
Patients also need to carry an ID card with them that can inform medical personnel of important manufacturer-specific details regarding the device. Security personnel may request that patients present this card because the device may set off security systems in airports and other high-security areas.
Alan Cheng, M.D.