Introduction to the CardioWest Total Artificial Heart (TAH)

The CardioWest Total Artificial Heart (TAH), now widely recognized as the SynCardia TAH, represents a landmark achievement in mechanical circulatory support (MCS). Unlike Left Ventricular Assist Devices (LVADs) which support a failing heart, the CardioWest TAH is designed to replace the function of both the left and right ventricles entirely. This device serves as a critical bridge-to-transplant (BTT) therapy for patients suffering from biventricular failure who are at imminent risk of death.

As an orthopedic and clinical specialist perspective, the integration of such high-stakes mechanical devices requires a deep understanding of fluid dynamics, materials science, and the physiological impact on the patient’s musculoskeletal and systemic health. This guide provides an exhaustive review of the CardioWest TAH, focusing on the engineering that makes it the gold standard in temporary mechanical heart replacement.

Technical Specifications and Biomechanical Design

The CardioWest TAH is a pneumatic, pulsatile device that mimics the anatomy and function of the native human heart. It is constructed to be orthotopically placed, meaning it occupies the same space where the native heart once resided.

Materials and Construction

The device is engineered for biocompatibility and durability under high-stress cycles.

• Housing: Rigid, polycarbonate plastic shells that protect the internal components.
• Diaphragms: Multi-layered, flexible polyurethane membranes that act as the "muscles" of the pump, facilitating blood ejection.
• Valves: Four mechanical tilting-disk valves (Medtronic-Hall) that ensure unidirectional blood flow, mirroring the tricuspid, pulmonary, mitral, and aortic valves.
• Pneumatic Actuation: External drive consoles (such as the Freedom® portable driver) provide bursts of compressed air to move the diaphragms, creating a pulsatile flow.

Biomechanical Mechanism

The TAH operates via a pneumatic displacement system. During the systolic phase, air is pumped into the space behind the diaphragm, pushing it forward and ejecting blood into the systemic and pulmonary circulations. During diastole, the air is vented, allowing the diaphragm to collapse and the chamber to fill with venous blood.

Clinical Indications and Surgical Applications

The CardioWest TAH is indicated for patients with end-stage biventricular failure who are ineligible for LVAD therapy due to anatomical constraints or severe right-sided heart failure.

Patient Selection Criteria

Candidates for the CardioWest TAH must meet stringent clinical requirements:
1. Irreversible Biventricular Failure: Confirmed by hemodynamic monitoring.
2. Transplant Candidacy: The patient must be on the active waiting list for a donor heart.
3. Anatomical Suitability: The patient’s thoracic cavity must be large enough to accommodate the device volume.
4. Ineligibility for LVAD: Patients where right ventricular support is deemed insufficient or impossible.

Surgical Protocol

The implantation is a major cardiac surgical procedure performed under cardiopulmonary bypass.
* Excision: The native ventricles are removed, leaving the atria intact.
* Anastomosis: The CardioWest TAH cuffs are sutured to the remnant atria and the great vessels (aorta and pulmonary artery).
* Driveline Tunneling: The pneumatic drivelines are tunneled through the abdominal wall to minimize infection risk and provide a secure exit point for the external driver connection.

Maintenance, Sterilization, and Usage Protocols

Because the CardioWest TAH is an externalized system, maintenance is a life-critical task for both the clinical team and the patient.

Sterile Field Management

The driveline exit site is the primary pathway for bacterial entry.
* Dressing Changes: Must be performed using aseptic technique, typically involving chlorhexidine gluconate and sterile occlusive dressings.
* Stabilization: The driveline must be anchored securely to the skin to prevent "pistoning," which can cause tissue trauma and infection.

Mechanical Maintenance

• Drive Console Checks: Daily inspection of the pneumatic console for battery life, alarm history, and air pressure output.
• Backup Systems: Every patient must have a secondary, redundant driver console immediately available in the event of a primary equipment failure.

Patient Outcome Improvements

The CardioWest TAH has revolutionized the landscape of heart transplantation. By replacing the failing organ, it allows for:
* Hemodynamic Stabilization: Immediate resolution of pulmonary hypertension and systemic congestion.
* End-Organ Recovery: Improvement in renal and hepatic function, which are often compromised in patients with biventricular failure.
* Physical Rehabilitation: Once stable, patients can often participate in physical therapy, which is crucial for maintaining muscle mass and bone density—critical factors for a successful post-transplant recovery.

Risks, Side Effects, and Contraindications

Despite its efficacy, the CardioWest TAH carries significant risks:
* Thromboembolism: Despite anticoagulation, the risk of clot formation within the mechanical chambers remains.
* Infection: Driveline infections or mediastinitis can be life-threatening.
* Bleeding: Often related to the necessary aggressive anticoagulation therapy (e.g., Warfarin or Heparin).
* Neurological Events: Stroke or transient ischemic attacks due to potential emboli.

Absolute Contraindications

• Small body surface area (BSA) that prevents the device from fitting in the chest.
• Irreversible non-cardiac organ failure (e.g., end-stage renal failure not expected to recover).
• Inability to comply with the rigorous anticoagulation and maintenance regimen.

Frequently Asked Questions (FAQ)

1. How long can a patient survive on the CardioWest TAH?

The device is intended as a bridge to transplant. Some patients have been supported for over a year, but the duration depends on the availability of a donor heart and the patient's individual recovery.

2. Does the CardioWest TAH produce a heartbeat?

Yes. Because it is a pulsatile device, it generates a palpable pulse, unlike many continuous-flow LVADs.

3. Can the patient go home with this device?

Yes, with the Freedom® portable driver, many patients are successfully discharged home while awaiting a transplant.

4. What is the most common complication?

Bleeding and infection are the most frequent complications. Meticulous driveline care is the best defense against infection.

5. Is the TAH permanent?

No. It is a temporary device designed to support the patient until a human heart transplant is performed.

6. How is the anticoagulation monitored?

Patients require frequent blood tests to monitor INR (International Normalized Ratio) and PTT to ensure the blood is thin enough to prevent clots but not so thin as to cause hemorrhage.

7. What happens if the power goes out?

The driver console has internal batteries. Additionally, patients are trained to keep a manual emergency pump available at all times.

8. Can patients exercise with the TAH?

Yes. Physical therapy is encouraged to keep the patient strong for the eventual transplant surgery. Exercise must be cleared by the transplant team.

9. How is the device sized?

Surgeons perform pre-operative imaging (CT or MRI) to measure the thoracic cavity and ensure the device fits without compressing surrounding structures.

10. Does the patient need to be on immunosuppressants?

While the TAH itself does not require immunosuppression, the patient will eventually require it after their human heart transplant.

Conclusion

The CardioWest TAH remains a pinnacle of mechanical circulatory support. For patients facing the bleak reality of end-stage biventricular failure, this device offers more than just time; it offers a physiological "reset" that allows the body to stabilize and prepare for the ultimate curative therapy: a heart transplant. Through rigorous surgical technique, dedicated maintenance of the driveline, and a comprehensive multidisciplinary approach, the CardioWest TAH continues to save lives where other interventions fail. As technology evolves, we anticipate smaller, more efficient systems, but the fundamental principle of total mechanical replacement remains a cornerstone of advanced cardiac care.