Ventricular assist devices (VADs) can either support the right (RVAD) or left (LVAD) ventricles and were initially intended to be a bridge-to-transplant (BTT) in heart failure. Modern continuous flow VADs are also being used for destination therapy (DT) for those who are not candidates for cardiac transplantation or are too ill to wait for a donor. The options available for advanced heart failure therapy are growing each year, so physicians (especially intensivists) are increasingly likely to encounter patients with VADs. What are some basic things healthcare providers should know?
As shown in the video above, continuous flow VADs like the Heartmate series are based on the simplicity of an Archimedes screw rotating in a magnetic field up to 10,000 times per minute! This rotary action propels blood flow from the inflow cannula (typically the apex of the left ventricle) to the outflow cannula (proximal aorta) up to 10 liters per minute. Because of the constant flow, patients may not have a palpable pulse depending on their underlying ventricular function.
This action “assists” the left ventricle by promoting forward systemic flow, but it’s important to keep the right-sided heart failure in mind as well and consider pulmonary vasodilators with inotropic support of the right ventricle if needed. Worst case scenario, a biventricular VAD can support both sides of the heart. 🙂
Pump speed (as RPM) is the only variable programmed by an operator, but a VAD machine will read out others parameters:
- Power – basically the energy needed to create flow. An acute increase in power requirements could be related to thrombosis within the LVAD and warrants additional anticoagulation and/or thrombolytics.
- Flow – a surrogate for the cardiac output. For a fixed RPM, a higher flow rate implies decreased resistance as in sepsis or vasodilation. A lower flow suggests decreased intravascular volume (hypovolemia, bleeding, etc.)
- Pulsatility index (PI)- represents the balance of native ventricular function and unloading by the continuous flow VAD. An increase could suggest recovery of ventricular function whereas a decrease represents hypovolemia, worsening ventricular function, and excessive pump speed.
Other considerations which actually make a lot of sense:
- These patients require anticoagulation and are pre-disposed to clot formation due to stasis within the native heart, especially around the aortic valve. Look out for signs of embolic phenomena.
- Dysrhythmias are often caused by the inflow cannula irritating the ventricular septum. Fluid resuscitation and slowing the pump speed can allow the ventricle to fill more and alleviate the irritation.
- Aortic insufficiency (“regurgitation”) is fairly common the longer VADs stay in, and this can actually create a loop within the VAD. Left ventricle -> VAD inflow -> VAD outflow -> aorta -> back into the left ventricle through an incompetent aortic valve.
- Hemolysis from physical agitation of red blood cells making contact with the rotor pump. Monitor carefully whenever the pump speed is adjusted.
- Infections can occur in the VAD drive line or in a pocket housing the pump. Typical organisms include Staphlococcus, Enterococcus, and Pseudomonas. Empiric antibiotics should be initiated and sometimes surgical debridement is required for deeper wound infections.
- Arrest: In the event of cardiopulmonary arrest, if the VAD is still functional, do NOT perform chest compressions as you risk dislodging the VAD cannulas. Instead, perform a “chemical code” by administering only drugs from the ACLS protocol. There are many articles which suggest that CPR is safe in VAD patients, but in general, the evidence is scant.