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The Different Types of Implantable Cardioverter Defibrillator

Implantable cardioverter defibrillators (ICDs) are life-saving medical devices that monitor and treat dangerous heart rhythms. For patients at high risk of sudden cardiac arrest due to conditions like ventricular tachycardia or heart failure, ICDs provide continuous, automatic intervention that can prevent fatal events.

There are multiple types of implantable cardioverter defibrillators, each suited to different cardiac conditions and patient needs. Understanding how these devices work—and when to use each type—is essential for professionals like clinicians, biomedical engineers, and hospital equipment procurement teams managing ICD selection, maintenance, and replacement.

In this guide, we’ll explore ICD classifications, key functions, and how PartsSource supports healthcare providers and HTM teams with critical ICD components and services.

Types of Implantable Cardioverter Defibrillators

 

Traditional Transvenous ICDs

Transvenous ICDs are the most widely used type of implantable defibrillator. The pulse generator is implanted under the skin, usually near the collarbone, with one or more leads (wires) threaded through veins and positioned directly inside the heart.

These devices monitor for ventricular arrhythmias, such as ventricular tachycardia (VT) or ventricular fibrillation (VF), and deliver life-saving shocks when needed. Many also include pacemaker capabilities to manage bradycardia (slow heart rhythms).

Transvenous ICDs are typically used in patients with a history of cardiac arrest, high arrhythmia burden, or who require pacing for rate control.

Subcutaneous ICDs (S-ICDs)

S-ICDs are a newer generation of ICDs that eliminate the need for leads inside the heart. Instead, a single electrode is placed under the skin along the left side of the chest, and the pulse generator is implanted near the rib cage.

S-ICDs reduce the risk of complications associated with transvenous leads, such as infection, vein obstruction, or lead dislodgement. However, they do not provide pacing therapy, making them unsuitable for patients with bradycardia or those needing cardiac resynchronization.

S-ICDs are often used in younger patients, those with a high infection risk, or individuals who need shock-only therapy for ventricular arrhythmias.

Cardiac Resynchronization Therapy Defibrillators (CRT-Ds)

CRT-Ds combine traditional ICD functionality with cardiac resynchronization therapy (CRT), which is used in patients with heart failure and abnormal ventricular conduction.

These systems use three leads: one in the right atrium, one in the right ventricle, and one threaded through the coronary sinus to stimulate the left ventricle. The device synchronizes contractions between the left and right sides of the heart, improving cardiac output, reducing symptoms, and decreasing hospitalizations.

CRT-Ds are reserved for select patients with reduced ejection fraction, wide QRS complex, and persistent heart failure symptoms despite optimal medical therapy.

Key Functions of ICDs

 

Defibrillation and Cardioversion

The primary role of any ICD is to detect life-threatening arrhythmias and deliver a therapeutic shock. High-energy shocks, known as defibrillation, restore normal rhythm during ventricular fibrillation or pulseless VT. ICDs also perform cardioversion, a lower-energy synchronized shock to treat fast but organized rhythms.

Modern ICDs can distinguish between atrial fibrillation, supraventricular tachycardia, and ventricular arrhythmias, helping prevent unnecessary or inappropriate shocks.

Anti-Tachycardia Pacing (ATP)

ATP is a feature in most transvenous ICDs that delivers rapid, low-energy pulses to stop ventricular tachycardia before it escalates into a life-threatening rhythm. This can eliminate the need for a full shock and reduce discomfort for the patient while conserving battery life.

ATP is particularly beneficial for patients with frequent, sustained episodes of monomorphic VT.

Pacemaker Capabilities

Most transvenous ICDs also act as pacemakers, maintaining an appropriate heart rate in patients with bradycardia. They can provide single-chamber or dual-chamber pacing, depending on patient needs.

Pacing helps stabilize heart rhythm, especially in patients with conduction system disease, heart block, or medication-induced slow rhythms.

Choosing the Right ICD for Patients

Selecting the correct ICD requires evaluating the patient’s cardiac condition, history of arrhythmic events, and overall risk profile. Factors to consider include:

  • Prior cardiac arrest or sustained VT/VF

  • Need for pacing or CRT

  • Risk of lead complications or infection

  • Age and expected device longevity

  • Anatomy and venous access

Cardiologists, electrophysiologists, and biomedical engineers collaborate to choose and program the appropriate device. Precise device programming and follow-up testing help minimize shock frequency and optimize therapy.

How PartsSource Supports ICD Management

Managing ICDs extends beyond implantation. It includes replacement parts, ongoing monitoring, and device servicing—especially for hospitals managing high patient volumes or complex cardiac cases.

PartsSource supports this process by offering:

  • Replacement parts of defibrillators like leads, batteries, and accessories for multiple ICD systems

  • Access to both OEM and high-quality aftermarket components, supporting budget-conscious procurement

  • Support for biomedical equipment, including ICDs, through centralized sourcing and real-time availability

  • Medical equipment repair service for inoperative or damaged ICD-related systems

  • Fast shipping on different types of AEDs and parts to reduce downtime and keep devices available for emergency use

Whether you're supporting surgical ICD implantation teams or managing ICD inventories across departments, PartsSource helps you maintain operational control and ensure healthcare is Always On™.

Conclusion

ICDs are essential tools in modern cardiac care, offering continuous monitoring and life-saving therapy for patients at risk of sudden cardiac death. The types of implantable cardioverter defibrillators—including transvenous ICDs, S-ICDs, and CRT-Ds—are designed to meet a wide range of clinical needs.

For healthcare providers, clinical engineers, and HTM teams, understanding these devices and supporting their proper function is vital to delivering safe, effective care. Selecting the right system, ensuring routine monitoring, and having access to replacement components and support are key to long-term success.

Explore PartsSource for replacement parts, ICD-related accessories, and service solutions that help your team stay prepared and proactive in the management of cardiac devices.