A. The modern implantable cardioverter—defibrillator (ICD) is a multifunctional, multiprogrammable electronic device designed to abort life-threatening arrhythmias. It is programmed to automatically detect and manage episodes of ventricular tachycardia (VT), ventricular fibrillation (VF), or bradycardia. Current ICDs are able to deliver multitiered therapies, which may include a combination of antitachycardia pacing (ATP), cardioversion, and defibrillation. The devices also offer bradycardic support, which may include rate-responsive single- or dual-chamber pacing and automatic mode switch function. Modern ICDs are able to deliver resynchronization therapy, a significant advancement in the management of heart failure. The devices are also able to store electrograms (EGMs), which can be easily retrieved. This function can be of immense use for follow-up management of the patient and programming of the device.

Multiple clinical trials have demonstrated the efficacy of ICDs to accurately detect and manage sudden cardiac death (SCD). The ICDs are superior to conventional therapy, with medications in both primary and secondary prophylaxis of SCD. The majority of patients who have indications for an ICD implant are those with left ventricular (LV) dysfunction, both ischemic and nonischemic.

B. Mirowski first introduced the concept of an ICD in the 1960s, with the first human implant reported in 1980. The early ICD implantations required a thoracotomy approach for placement of an epicardial lead system. Subsequent advancements in device and lead technology over the last 30 years have significantly reduced the size of the pulse generator, yet improved the programmability and diagnostic data stored within the device. An improved understanding of VF, defibrillation, and cardiac pacing has resulted in the development of biphasic shock waveforms and transvenous pace/defibrillation lead systems that preclude the need for epicardial patches. As a result, modern ICDs are more compact devices, with expansive programming capability placed by a transvenous approach. The newest generation of devices has the added capability of trans-telephonic interrogation.

A. The current-day ICD is a sophisticated and intelligent computer. It consists of a generator and leads. The ICD generator consists of a battery, capacitors, DC—DC converter using an oscillator rectifier mechanism, a microprocessor, and telemetry communication coils and their connections. The generator serves as an active electrode within the shocking configuration in most of the modern ICDs and is thus called the “hot can.” The battery used in most of the ICDs is a lithium—silver vanadium oxide cell. This can generate approximately 3.2 V at full charge. Because most ICDs use two batteries connected in series, the full initial voltage is approximately 6.4 V. The generator has capacitors that can charge within 7 to 30 seconds to store up to 30 to 40 J of energy. This can be delivered to the heart within a 10- to 20-millisecond interval when therapy is required.

B. The three essential functions of the ICD—tachycardia detection, tachycardia therapy, and bradycardia pacing—are delivered through the active electrodes, which are the noninsulated segments of the leads. Most of the current-day leads have sensing and pacing electrodes at the tip and a distal (right ventricle) and proximal (superior vena cava) shocking coil. The function of ventricular sensing and pacing is achieved by a technology similar to that in pacemakers. This is done through two “dedicated bipolar” electrodes at the distal end of the right ventricular (RV) lead (tip/ring). Sometimes, it may be achieved by “integrated bipolar” electrodes, wherein the bipole is formed by the tip of the ventricular lead and the distal shocking coil (tip/coil). Ventricular pacing in biventricular ICDs is from the tip of the RV and LV leads, respectively, to either the ring (true bipolar) or the distal shocking coil (integrated bipolar). The sensing could be from both RV and LV leads but could give rise to false tachycardia detection due to the problem of “double counting.” It is for this reason that the newer devices restrict the sensing function to the RV lead alone.

C. For the delivery of shock therapy, most systems now incorporate a combined RV coil, superior vena cava coil, and active pulse generator can or sometimes a single RV coil with a hot can active pulse generator. Modern technology makes it feasible to incorporate all these electrodes and coils in a single lead implantable in a manner similar to a pacemaker.

A. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities. These are the most current guidelines for the implantation of ICDs. The guidelines stratify the various indications as class I, class II (a and b), and class III on the basis of the data from clinical trials and opinion of a panel of experts.

B. Class I indications. These are clinical situations or conditions for which there is evidence and/or general agreement that ICDs are useful and effective.

(1) Survivors of SCD secondary to VF or hemodynamically unstable VT

(2) Syncope of unknown etiology with inducible VF or hemodynamically significant VT during electrophysiology study

(3) Structural heart disease and spontaneous hemodynamically unstable or stable VT

(4) Ischemic cardiomyopathy, New York Heart Association (NYHA) class I, and a left ventricular ejection fraction (LVEF) < 30% who are at least 40 days post myocardial infarction (MI)

(5) Ischemic cardiomyopathy, NYHA class II or III with an LVEF < 35% who are at least 40 days post-MI

(6) Ischemic cardiomyopathy, ejection fraction (EF) < 40%, nonsustained ventricular tachycardia, and inducible VF or sustained VT at electrophysiology study Nonischemic cardiomyopathy, NYHA class II or III, and LVEF < 35%.

C. Class IIa indications. These are conditions for which there is conflicting evidence about the usefulness of ICD therapy, with the weight of evidence/opinion in favor of usefulness/efficacy.

1. Unexplained syncope with significant LV dysfunction and nonischemic cardiomyopathy

2. Normal or nearly normal LVEF with sustained VT

3. Patients with hypertrophic cardiomyopathy and at least one risk factor for SCD

4. Patients with arrhythmogenic RV dysplasia with at least one risk factor for SCD

5. Patients with long QT with syncope or VT while taking β-blockers

6. Patients waiting heart transplantation (nonhospitalized)

7. Patients with Brugada with a history of syncope or VT but no episodes of cardiac arrest

8. Patients with catecholaminergic polymorphic VT with syncope or sustained VT while taking β-blockers

9. Patients with cardiac sarcoid, giant cell myocarditis, or Chagas disease.

D. Class IIb (usefulness/efficacy is less well established by evidence/opinion)

1. Nonischemic cardiomyopathy with an EF < 35% and NYHA class I

2. Long QT and risk factors for SCD

3. LV noncompaction patients

4. Patients with familial cardiomyopathy and a predisposition to SCD

5. Patients with structural heart disease and syncope but with no identifiable etiology

E. Class III indications/contraindications. These are conditions for which there is a general agreement that ICDs are not useful and possibly harmful. These include patients with a structurally normal heart and syncope without any inducible ventricular arrhythmias. ICDs should also be avoided in patients with VT and a treatable/ablatable cause (Wolff-Parkinson-White syndrome, outflow tract VTs, fascicular VTs, etc.) or a reversible cause (acute MI, myocardial ischemia, electrolyte imbalance, drug toxicity, or trauma). It is also important to avoid using ICDs in patients with severe psychiatric illnesses or in patients with terminal illnesses, where the expected life span is less than 12 months. ICDs could do more harm than good in patients with incessant ventricular arrhythmias, where it is important to control the arrhythmia before ICD implantation to avoid recurrent painful shocks. ICDs are also contraindicated in patients with NYHA class IV heart failure that are drug refractory and are not candidates for heart transplantation or cardiac resynchronization therapy (CRT).

A. Device implantation. Currently, available devices are small enough to allow implantation in the left pectoral region. Animal studies have shown that the defibrillation efficacy of the hot-can ICDs is superior in the left pectoral or axillary regions followed by the right pectoral and then the abdominal sites. A right pectoral system may be necessary in patients who have vascular access problems on the left side or who have undergone pectoral surgery (e.g., mastectomy). For patients with high defibrillation thresholds (DFTs), additional lead placement, such as a subcutaneous array/coil, an azygous coil, a coronary sinus coil, or an epicardial patch, may be necessary. Epicardial patch placement is usually reserved for patients who have failed to meet implantation criteria with a transvenous lead system or if there has been previous bilateral pectoral or tricuspid valve replacement surgery.

For pectoral implants, a single 2″ to 3″ incision is made transversely below the clavicle, about 1 cm below and parallel to the deltopectoral groove. Transvenous lead placement is achieved through a subclavian vein puncture or by cephalic vein cutdown. An “extrathoracic” subclavian vein puncture or cephalic vein cutdown for access minimizes the risk of pneumothorax and also the risk of lead failure due to subclavian crush injury.

B. Lead placement. The lead is advanced to the RV apex under fluoroscopic guidance, where the tip is secured via an active fixation screw or embedded in the trabeculae with passive fixation tines. It is important to assess the quality of signals at the time of implant, as it is the best guide to the adequacy of long-term sensing of the lead. The DFT is optimized with the lead placed at the RV apex; therefore, this position is often preferred even if there is compromise of the sensing thresholds. If there is already a pacemaker lead in the RV apex, then septal placement of the lead tip is chosen so that the lead tips are at maximal distance from each other to avoid device—device interactions. On occasion, placing an additional pacing-sensing lead in the right ventricle may be necessary when the defibrillation efficacy and pacesense function of the leads are optimized at different locations.

C. Threshold studies. The lead is tested for pace-sense thresholds using an external high-voltage system analyzer or pacing system analyzer. In general, an acute pacing threshold of 2 V or less, R-wave amplitude of 5 mV or more, and lead impedance within the accepted range of the manufacturer (typically 300 to 1,200 Ω) are
necessary to meet the implant criteria. The lead is secured within the pocket with a suture sleeve tie-down. If the device uses an atrial and/or an LV lead, then these are implanted at this time. The leads are attached to the pulse generator and the system is placed in either a submuscular or a subcutaneous pocket. The pulse generator should be placed with excess lead coiled posteriorly to reduce the risk of damaging the leads at the time of generator change and to maximize the ability to communicate with an external programming wand. The device is then interrogated to assure appropriate communication. Pace-sense thresholds are again tested by telemetry to demonstrate consistency.

D.

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