In patients with a left ventricular assist device (LVAD), spectral Doppler waveforms are altered due to continuous flow provided by the pump in the device:
- waveforms are monophasic with a constant antegrade flow and no flow below the baseline
- the waveform is typically parvus-tardus with a slow systolic upstroke and rounded systolic peak
- less commonly there may be non-pulsatile flow with no systolic peak
- the systolic peak is thought to be due to intrinsic residual myocardial reserve pumping some of the blood, whereas lack of a systolic peak is thought to occur when the left ventricle is simply acting as a passive conduit and all blood is being pumped by the device
- peak systolic velocity (PSV) is reduced
These findings have been demonstrated diffusely in multiple arterial beds, including the carotid, vertebral, subclavian and common femoral arteries.
Radiographic features
Echocardiography
Spectral Doppler-derived indices of intracardiac hemodynamics, measured as part of repeated comprehensive echocardiographic studies, are used to serially assess cardiac structure and function. Echocardiography is typically performed in the following settings 3:
- pre-operative assessment
- typically a routine transthoracic echocardiography protocol, with a particular focus on variables which would contraindicate surgical placement of the LVAD, including 3
- moderate to severe mitral valve stenosis
- moderate to severe aortic valve regurgitation
- tricuspid valve stenosis
- typically a routine transthoracic echocardiography protocol, with a particular focus on variables which would contraindicate surgical placement of the LVAD, including 3
- perioperative monitoring
- conducted using a transesophageal approach
- allows continuous assessment of the positioning and angulation of the cannulae during introduction 4
- subsequent (spectral and color flow) Doppler assessment of the flow egress through the inflow cannula should reveal a laminar flow pattern, with a maximum velocity <2 m/s
- the patency of the outflow cannula should also be sought
- color flow Doppler is also used to screen for the presence of the following, which may portend a complicated clinical course:
- occult patent foramen ovale (PFO)
- significant aortic insufficiency
- right ventricular dysfunction
- post-surgical evaluation
- routine surveillance