A summary of total artificial heart – part man, part machine..
Used as a bridge to cardiac transplantation when the eligible patient is at risk of imminent death from biventricular failure.
- Implanted Device (160 grams)- 2 ventricles (secured by medical grade Velcro), 2 inflow cuffs, 2 cannulae, 2 outflow grafts
- Companion Driver
- Delivers approximately 70ml stroke volume per cycle with a maximum output of 9L/min.
- Patient should have a total BSA > 1.7m2
Why use it?
- Decrease CVP, overcome PAP, Improve cardiac output, hence organ perfusion. Also allows patient to come off anti-rejection therapy.
- Eliminates complications associated with LVAD – Avoid the need for long term inotropes, Eliminates issues with LV thrombus, Arrythmias, Right heart failure, dependency on aortic valve function.
How does it work?
The native/ transplanted heart is explanted, leaving behind a small rim of atria that is sutured onto the inflow cuffs. Blood returning from the venous and pulmonary circulation enters the tAH ventricles via the inflow cuffs, with air being let out through the cannulae which results in depression of the diaphragm to allow Partial Filling (50-60ml). Once this volume of filling is achieved, air is let in that pushes the diaphragm which in turn pushes the volume of blood, through the outflow grafts (mimicking the through the RVOT, LVOT). This is known as Full Eject (look for the peak pressure rise). There are tilting discs located in the “atrio-ventricular” side that prevents retrograde flow during ejection phase, as well as discs on the “outflow tract” that prevents antegrade flow during the filling phase.
Recognizing Pericardial Tamponade
Detecting tamponade in a patient who has had a TAH-t done is different to normal practice. For one, the patient does not have a normal size right atria and the ventricle of the TAH-t, is non-compressible. The features to look for on the console monitor are – decreased in fill volume (ie < 50ml), decrease cardiac output and a decrease in flow on the Flow-time curve. An echo could be performed to visualise a dilated IVC. In the TOE shown below, the patient developed a tamponade over a period of days, more than a week after implantation.
Things to note:
- Patients will not have electrical impulse once they have had a TAH. Therefore, ECG monitoring is not needed. Heart rate is set at 125+/- 15bpm
- CPR and inotropes are ineffective in the setting of cardiac arrest.
- A backup console/ Driver should always be available in case of mechanical or battery failure.
- Hospital air source can be used to connect to the driver.
- Anticoagulation includes aspirin and dipyridamole.
- The drivelines look similar to calf compressors tubing but do not function in the same way!
Copeland JG et al. Cardiac replacement with a total artificial heart as a bridge to transplantation. N Engl J Med 2004;351:859–67.Tags: cardiomyopathy heart transplant TOE total artificial heart