Cardiac Implantable Electronic Devices: Internal Cardioverter-Defibrillators

Device Overview and Indications

• The traditional ICD system consists of a pulse generator located in the left chest wall and endovascular leads that extend into the heart.
• The ICD constantly surveils for ventricular tachyarrhythmias using the endovascular leads that sense the heart’s native electrical activity.
• When the ICD detects ventricular tachycardia or ventricular fibrillation, the device initiates a preprogrammed sequence of antitachyarrhythmia therapies.
  • This typically includes a burst of rapid antitachycardia pacing, followed by defibrillation if the ventricular tachyarrhythmia persists.
  • The defibrillation shock is delivered through a thickened portion of the endovascular lead, often described as the shock coil.
• ICDs are indicated for both primary and secondary prevention of ventricular tachyarrhythmias.
  • Patients with ICDs implanted for primary prevention typically have symptomatic heart failure with significantly reduced ejection fraction due to prior myocardial infarction or dilated cardiomyopathy.¹
  • The main secondary indications for ICDs include prior ventricular fibrillation arrest, hemodynamically unstable ventricular tachycardia, and ventricular tachyarrhythmia after a ST-elevation myocardial infarction.²
• In addition to defibrillation, ICDs are also capable of pacing the heart, a function similar to that of a traditional pacemaker.

Risk of EMI

• EMI can interfere with how ICDs sense native cardiac electrical activity.
• EMI can be mistakenly interpreted as ventricular tachycardia or ventricular fibrillation by an ICD during surgery, leading to inappropriate defibrillation (Figure 1).

• The most common source of perioperative EMI is monopolar electrosurgery, commonly used by surgeons.
  • With monopolar electrosurgery, alternating current is emitted from the electrode tip used by the surgeon to cut or coagulate tissue.
  • This current is dispersed through the patient to a grounding electrode pad.
  • Current crossing the path of the ICD can generate EMI (Figure 1) and lead to inappropriate sensing or shocking.

• In a study investigating the risk of EMI based on the anatomical location of surgery, investigators concluded that surgeries below the umbilicus confer a minimal risk of clinically significant EMI for patients with ICDs.⁴
• In contrast to monopolar electrosurgery, procedures that utilize bipolar electrosurgery have a low risk of clinically significant EMI, given the minimal current dispersion associated with bipolar electrosurgery.

Perioperative Management

Preoperative Planning

• ICDs should be interrogated within 3-6 months prior to surgery, consistent with the consensus of the American Society of Anesthesiology (ASA) task force on perioperative management of patients with cardiac implantable electronic devices.⁵
• The ICD device interrogation report provides important information about device function, programming, and pacer-dependence (Table 2).

Magnet Versus Reprogramming

• If medical records are unavailable, a chest radiograph can help distinguish the presence and type of ICD device.
• Determining a plan for managing perioperative EMI prior to surgery is critical (Figure 2).
• Surgeries above the umbilicus pose a risk of EMI that can trigger inappropriate shocks for patients with traditional ICDs. In addition, pacer-dependent patients with ICDs remain susceptible to inappropriate sensing from EMI.
• Disabling shock therapy can be accomplished either with preoperative device reprogramming or magnet application.
• The decision whether to use a magnet is individualized and must consider the surgical location, the patient’s history of defibrillation, any concomitant pacing requirement, and resource availability.
• Importantly, unlike pacemakers, a magnet does not convert the ICD to an asynchronous pacing mode.
• Patients who are dependent on the pacing function of their ICD require device reprogramming, rather than magnet application.
• Of note, anytime the ICD defibrillation function is programmed off, external defibrillation pads and supplies should be placed on the patient or made immediately accessible.

Postoperative Management

• The ASA and Heart Rhythm Society guidelines recommend interrogating a device within one month following surgery.⁶
• Certain situations merit immediate postoperative interrogation, including external cardioversion or defibrillation, transcutaneous pacing, and emergency surgery where preoperative interrogation was not possible.

ICD Malfunction

• There are multiple causes of unexpected ICD failure, including lead migration, lead fracture, and battery malfunction.
• ICD malfunction can cause two critical issues: failure to defibrillate when indicated and inappropriate defibrillation.
• In some instances, inappropriate defibrillation may occur when the ICD senses rapid supraventricular rhythms, including atrial fibrillation and supraventricular tachycardia.

ICD Lead Removal Complications

• Serious problems related to an ICD lead, including infection, lead fracture, and significant venous obstruction, can necessitate the extraction of a lead.
• Lead extraction is associated with rare, yet highly morbid complications including myocardial rupture, tamponade, and damage to the tricuspid valve.
• Risk factors for life-threatening ICD removal complications include longer lead implant duration, lack of operator experience, and the need to extract more than 3 leads.
• High-risk ICD lead extractions are typically performed in the operating room under general anesthesia to facilitate transesophageal echocardiography monitoring for complications.

Novel Subcutaneous ICDs

• To avoid the known complications associated with traditional endovascular ICD leads (vessel stenosis, infection), a novel “subcutaneous ICD” has been developed over the past decade.
• The subcutaneous ICD employs a single lead in the subcutaneous tissue superficial to the sternum, obviating the need for endovascular leads.
• Because the subcutaneous ICD lead is not in direct contact with the heart, the system must simulate a surface-level electrocardiogram to monitor intracardiac electrical activity.
• This broader sensing “antenna” generally renders subcutaneous ICDs more susceptible to the effects of electromagnetic interference.
• There is minimal clinical evidence to guide the perioperative management of subcutaneous ICDs.
• At a minimum, surgeries above the groin should be considered to have a risk of clinically significant EMI.⁷
• Unlike traditional ICDs, subcutaneous ICDs are not capable of providing long-term pacing.