Total Artificial Heart (TAH) implantation

23-year-old man with non-ischemic cardiomyopathy and end-stage biventricular heart failure who has just undergone a thoracotomy and cardiac surgery as a bridge to orthotopic heart transplant (clinical presentation initially withheld). AP chest radiograph without (Fig. 1) and with accompanying annotations (Fig. 2) demonstrate the normal post-operative appearance of a Total Artificial Heart (TAH) implantation. Both native ventricles have been removed as have all four native cardiac valves. The mechanical cardiac valves of the TAH are delineated (Fig. 2). The air-containing diaphragms related to the artificial right and left ventricle of this pneumatic pulsatile device should not be confused with myocardial chamber air, pneumopericardium, or pneumomediastinum and is a normal expected post-operative finding. The left ventricle pneumatic drive-line is seen exiting through a port in the left upper quadrant and connects to a bedside console. Two mediastinal and bilateral pleural drains are present. Note the pre-existing ICD leads have been amputated. AV-mechanical aortic valve; MV- mechanical mitral valve; PV- mechanical pulmonic valve; TV – mechanical tricuspid valve.     Diagnosis: Total Artificial Heart (TAH) implantation

Differential Diagnosis

None

 

Discussion

The total artificial heart (TAH) is presently used in the United States as a bridge for patients with end-stage biventricular heart failure awaiting heart transplantation. This mechanical device is a biventricular orthotopic pneumatic pulsatile pump with two separate artificial ventricles that replace the patient’s native ventricles. Each artificial semi-rigid polyurethane ventricle contains a seamless blood-contacting diaphragm, two intermediate diaphragms, an air diaphragm, and an inflow and outflow mechanical valve. A flexible polyurethane lined inflow connector is sewn to each atrial cuff of the recipient heart. Dacron graft outflow conduits are sewn to the patient’s native aorta and pulmonary artery, respectively. Wire reinforced conduits covered with Dacron in the transabdominal wall pathways connect to longer drivelines and to an external console that controls the mechanical heart. The external console consists of two pneumatic drivers, one primary and one backup, transport batteries, air tanks, and an alarm and computer monitoring system. Heart rate, the percentage of the cardiac cycle occupied by systole, and left and right driving pressures are manually controlled. The TAH is capable of pumping up to 9.5 liters of blood per minute.

 

Etiology

Worldwide, approximately 3,500 heart transplants performed every year. Unfortunately, about 800,000 people have an irreversible Class IV heart disease and therefore need a new organ. This disparity between supply of available organs for transplant and the demand for such has spurred considerable research into the use of non-human hearts since 1993. The TAH design used and implanted in the United States today is the modern version of the original Jarvik-7 artificial heart first implanted into Barney Clark in 1982. The TAH is primarily used as a bridge-to-heart transplant for transplant eligible patients dying from end stage biventricular failure.

 

Clinical Findings

The TAH replaces the patient’s diseased ventricles. The device reproduces the same blood flow path as the normal heart. The stroke volume of the device is 70 ml and it weighs roughly 160 grams. The TAH decreases the central venous pressure and increases the cardiac index, cardiac output and end-organ perfusion thereby increasing organ recovery. The pneumatic drive-lines connected to the bedside console may serve as a potential portal of entry for bacteria increasing the risk for infection for the duration of the device’s implantation. To reduce the risk of stroke from blood clots forming on the mechanical parts of the TAH patients must be anticoagulated.

Imaging Findings

Chest Radiography

• Sternal splitting thoracotomy (Fig. 1 and 2)
• Sternotomy may be left open in cases of peri-operative bleeding; closed at a later time
• ICD or pacer leads amputated; generator often left in place (Fig. 1 and 2)
• 1-3 mediastinal drains may be present (Fig. 1 and 2)
• Unilateral or bilateral pleural drains may be present (Fig. 1 and 2)
• 2 pneumatic drive-lines, one for each artificial ventricle, exit through a subcutaneous port in the left upper quadrant (Fig. 1 and 2)
• Artificial ventricles are not radiographically conspicuous
• 4 artificial mechanical valves can be identified (Fig. 1 and 2)
• Air-containing diaphragms for the artificial ventricles should not be misinterpreted for myocardial air, pneumopericardium, or pneumomediastinum (Fig. 1 and 2)

Prognosis

• TAH highest bridge-to-human heart transplant rate of any heart device
• 79% TAH recipients are successfully transplanted (46% controls not receiving TAH)
• Overall survival rate at 1-year: 70% among patients receiving the TAH ( 31% controls)
• 1-year and 5-year survival rates after heart transplant among these patients: 86% and 64%, respectively

CAVEATS

• All central venous catheters should terminate in a location far removed from the artificial mechanical tricuspid valve; catheter entanglement can cause device failure
• Radiologists should scrutinize all suture lines on post-operative CT scans in patients with suspected post-operative bleeding or hypotension as this may be a site of suture line dehiscence and bleeding that can be easily repaired

Selected Readings

1. Copeland JG, Smith RG, Arabia FA, Nolan PE, Gulshan PD, et al. Cardiac Replacement with a total artificial heart as a bridge to transplantation. N Engl J Med 2004; 351(9): 859-867.
2. http://www.syncardia.com/dldir1/8263_C026.pdf (accessed October 10, 2009).
3. Roussel JC, Sénage T, Baron O, Périgaud C, Habash O, et al. CardioWest (Jarvik) total artificial heart: a single-center experience with 42 patients. Ann Thorac Surg 2009; 87(1): 124-129; discussion 130.