Mandibular evaluation for device size, comprehensive cardiovascular assessment, NPO status for at least 8 hours, anticoagulation management, blood type and cross-match for massive transfusion protocol, and administration of prophylactic broad-spectrum antibiotics.
Immediate transfer to the Cardiothoracic Intensive Care Unit (CTICU). Strict monitoring of hemodynamic stability, maintenance of therapeutic anticoagulation (INR monitoring), driveline exit site care, physical therapy rehabilitation, and education on portable pneumatic driver operation. Long-term inpatient monitoring for potential infection or thromboembolic events.
1. Comprehensive Introduction & Overview
The SynCardia Total Artificial Heart (TAH) represents one of the most significant engineering marvels in modern cardiovascular medicine. Unlike a Ventricular Assist Device (VAD), which merely supplements the function of a failing natural heart, the SynCardia TAH is a biventricular replacement system. It is designed to replace both failing ventricles of the human heart, effectively serving as a bridge to transplant for patients suffering from end-stage biventricular heart failure.
The device is a pulsatile, pneumatically driven system that mimics the physiological function of the native heart. It is indicated for use in patients who are at imminent risk of death from irreversible biventricular failure and are awaiting a donor heart. By providing full circulatory support, the SynCardia TAH restores systemic perfusion, allows for the reversal of end-organ damage caused by low cardiac output, and stabilizes the patient’s clinical status while they await a suitable organ match.
2. Technical Specifications & Mechanisms
The SynCardia TAH is a sophisticated piece of bio-engineering. It consists of two independent ventricles made of a segmented polyurethane solution (specifically, Angioflex), which provides superior durability and hemocompatibility.
Key Components
- The Pump: Two independent chambers (left and right) that function as the artificial ventricles.
- Diaphragms: A flexible membrane within each chamber that moves to pump blood.
- Valves: Four tilting-disk mechanical valves that ensure unidirectional blood flow, mimicking the mitral, tricuspid, aortic, and pulmonary valves.
- Drivelines: Percutaneous tubes that connect the internal pump to the external driver.
- The Driver (Freedom Driver): A portable, wearable power unit that provides the pneumatic pulses required to actuate the diaphragms.
Physiological Mechanism
The system operates on a pneumatic principle. The external driver delivers precise pulses of compressed air through the drivelines into the space behind the polyurethane diaphragms. As the air pushes the diaphragm, blood is ejected from the ventricles into the systemic and pulmonary circulations. When the air pressure is released (systole to diastole transition), the diaphragm retracts, allowing the ventricles to fill with blood from the atria. This process is synchronized to maintain a physiological heart rate and cardiac output, typically adjustable between 5 to 9.5 liters per minute depending on the patient's metabolic demand.
3. Clinical Indications & Usage
The primary indication for the SynCardia TAH is "Bridge to Transplant" (BTT). It is specifically reserved for patients who are not candidates for standard VAD therapy due to anatomical constraints or the severity of biventricular failure.
Patient Selection Criteria
| Criteria Category | Requirement |
|---|---|
| Cardiac Status | End-stage biventricular failure (NYHA Class IV) |
| Anatomical Fit | Sufficient space in the thoracic cavity to accommodate the device |
| Urgency | Imminent risk of death; refractory to medical management |
| Transplant Eligibility | Must be a candidate for cardiac transplantation |
| Exclusion Criteria | Irreversible multi-organ failure, active systemic infection, contraindication to anticoagulation |
Clinical Goals
- Hemodynamic Stabilization: Restoration of blood pressure and tissue perfusion.
- End-Organ Recovery: Improvement of renal and hepatic function impaired by chronic venous congestion or low output.
- Nutritional Optimization: Allowing the patient to gain strength and weight in preparation for the physical trauma of a transplant.
4. Pre-Operative Preparation & Surgical Procedure
Pre-Operative Protocol
Patients are typically managed in the Intensive Care Unit (ICU) prior to surgery. Preparation includes:
* Multidisciplinary Review: Cardiology, Cardiothoracic Surgery, Anesthesiology, and Transplant Coordination.
* Diagnostic Imaging: Computed Tomography (CT) scan of the chest is mandatory to ensure the "fit" of the device within the patient’s pericardial space.
* Anticoagulation Profiling: Establishing a baseline for coagulation status to manage the high risk of thrombus formation.
The Surgical Procedure
The implantation is a major open-heart surgery performed under cardiopulmonary bypass.
1. Excision: The surgeon removes the native left and right ventricles, leaving the native atria, the aorta, and the pulmonary artery intact.
2. Cuff Attachment: Dacron cuffs are sutured to the remnant atria, the aorta, and the pulmonary artery.
3. Pump Insertion: The TAH is inserted and connected to these four cuffs using quick-connect couplings.
4. De-airing: Meticulous removal of all air bubbles from the system to prevent systemic embolization.
5. Driveline Tunneling: The drivelines are tunneled through the abdominal wall to connect to the external driver.
5. Post-Operative Recovery & Long-Term Management
Post-operative care is intensive and requires a specialized team.
- Anticoagulation: Patients must be on a lifelong anticoagulation regimen (typically Warfarin and Aspirin) to prevent mechanical valve thrombosis and thromboembolic events.
- Driver Transition: Patients are transitioned from the "Big Blue" hospital driver to the wearable "Freedom Driver" as they stabilize, allowing for increased mobility and physical therapy.
- Monitoring: Daily assessment of drive pressures, heart rate, and cardiac output. Periodic echocardiography ensures that the atrial cuffs and connections remain stable.
- Rehabilitation: Aggressive physical therapy is encouraged to prevent muscle atrophy while awaiting transplant.
6. Risks, Side Effects, and Contraindications
As with any mechanical circulatory support, the SynCardia TAH carries significant risks:
- Infection: The percutaneous driveline site is a constant portal for potential infection, which can lead to mediastinitis or sepsis.
- Thromboembolism: Risk of stroke or peripheral embolism due to blood contact with synthetic surfaces.
- Bleeding: Often exacerbated by the necessary anticoagulation therapy.
- Device Malfunction: Mechanical failure of the driver or the pump components.
- Renal/Hepatic Complications: Although the device improves organ function, the bypass and surgery carry inherent risks of acute kidney injury (AKI).
7. Alternative Treatments
When a patient is not a candidate for the SynCardia TAH, alternative strategies include:
1. Left Ventricular Assist Device (LVAD): If only the left ventricle is failing, an LVAD is preferred as it is less invasive.
2. Extracorporeal Membrane Oxygenation (ECMO): A temporary, short-term bridge for acute cardiogenic shock.
3. Inotropic Therapy: For patients who are not candidates for mechanical support, palliative inotropic support may be used.
4. Heart Transplant: The ultimate goal, though limited by donor availability.
8. Frequently Asked Questions (FAQ)
1. How long can a patient live with the SynCardia TAH?
The device is intended as a bridge to transplant. While some patients have lived with the device for several years, it is not designed to be a permanent "destination therapy" device in the same way modern LVADs are.
2. Can the patient walk and exercise with the TAH?
Yes. Once stabilized on the wearable Freedom Driver, patients are encouraged to participate in cardiac rehabilitation and light physical activity.
3. What happens if the power fails?
The Freedom Driver has redundant batteries and an AC power option. It is designed with alarms to alert the patient immediately of any power or pneumatic issues.
4. Is the TAH noisy?
The device makes a distinct "clicking" sound during each heartbeat, which is normal. Most patients become accustomed to the sound quickly.
5. Can a patient travel while on the TAH?
Travel is possible but requires extensive planning, coordination with the transplant center, and ensuring that backup equipment is available at the destination.
6. What is the biggest risk with the TAH?
The most significant risks are infection at the driveline exit site and thromboembolic events (stroke).
7. Does the TAH require an EKG?
No, the TAH is a fixed-rate device. It does not respond to the patient's native electrical activity; instead, it provides a consistent, set heart rate.
8. How is the device maintained?
The external driver is periodically serviced by the manufacturer. The internal components are permanent until the transplant surgery.
9. Are there age restrictions for this procedure?
While there is no strict chronological age limit, biological age, comorbidities, and the ability to tolerate major surgery are critical factors in patient selection.
10. What happens to the device during the transplant?
During the heart transplant surgery, the SynCardia TAH is surgically removed, and the donor heart is implanted into the atrial remnants and great vessels left behind.
9. Conclusion
The SynCardia Total Artificial Heart remains a life-saving intervention for the most critically ill cardiac patients. By providing a total replacement of ventricular function, it bridges the gap between near-certain mortality and the possibility of a life-extending heart transplant. While the procedure carries substantial risks and requires a high level of patient commitment, the clinical outcomes in terms of end-organ recovery and improved quality of life demonstrate its indispensable role in the modern cardiothoracic surgical armamentarium. Future advancements in driver portability and hemocompatibility will likely continue to improve the patient experience for those awaiting the "gift of life."