left ventricular assist device

Left ventricular assist devices (LVAD) are mechanical circulatory support device that are surgically implanted to aid pumping blood in patients with severe refractory cardiac failure. It may be used as a bridge to cardiac transplantation, or as destination therapy in patients who are not a transplant candidate.

Principle

The LVAD acts as a conduit, diverting blood from the left ventricle, through a mechanical pump, to the aorta. There are several different brands available; one commonly used device is the HeartMate II (Thoratec, Pleasanton, California) pictured in this article. The HeartMate II consists of an inflow cannula that diverts blood from the apex of the left ventricle into a pump. The pump then propels blood forward through an outflow Dacron graft to the ascending aorta. An electrical cable connects the LVAD to an external power source carried with the patient .

First generation devices pumped blood in a pulsatile manner, but current devices now pump with continuous flow either from an axial-flow pump (e.g. HeartMate II) or centrifugal/outward-flow pump (e.g. HeartMate 3 and HeartWare HVAD System). As a result, patients have no palpable pulse or a greatly diminished pulse .

Stroke is one of the more common complications due to the risk of thrombus formation within the LVAD components, therefore patients are maintained on anticoagulation.

Basic understanding of LVADs is important in radiology for several reasons:

  • it is prudent to recognize the device on thoracoabdominal imaging
  • Doppler waveforms throughout the arterial system are significantly altered (see: Doppler ultrasound findings with LVAD)
  • anticoagulation generally cannot be withheld or reversed for LVAD patients undergoing interventional radiology procedures due to the stroke risk, though in some instances the INR may be lowered to a degree
  • the HeartMate II, HeartMate 3 and HeartWare HVAD System are incompatible with MRI machines

Radiographic features

Device specific features

These device-specific features can help distinguish between devices :

  • HeartMate II
    • compared to other devices the HeartMate II device is inserted in a sub-diaphragmatic pocket rather than the pericardial space
    • uniquely features an impeller housing that is bell-shaped
    • of note, the inflow cannula angle relative to the pump should be >55° as smaller angles are associated with incorrect device positioning and thrombosis
  • HeartMate 3
    • circular shaped impeller unit
    • central inflow cannula
    • angled out-flow cannula
  • HeartWare HVAD System
    • circular shaped impeller unit
    • central inflow cannula
    • straighter out-flow cannula

Complications

Complications following LVAD insertion can include :

  • device malfunction
  • thrombosis
  • hemorrhage
  • drive-line infections
  • development of right-sided heart failure after LVAD implantation
  • Air embolism
  • infection
  • aortic regurgitation
  • pump thrombosis
  • stroke
  • cardiac dysrhythmia

Axial-flow type devices (e.g. HeartMate II) have been associated with the development of arteriovenous malformations of the gastrointestinal tract perhaps secondary to the development of acquired von Willebrand disease .

Treatment and prognosis

As long as patient use this device, LVAD function, patient perfusion, and mean arterial pressure are being assessed and anticoagulation (warfarin) and antiplatelet therapy have to be used.

See also