Effect of IFC Position on LV Unloading and Outcomes
We found that a laterally-directed IFC predicted significantly reduced
VAD FI at three and six months (Figure 6). Computational
studies8,9 have shown that increasingly lateral IFC
position causes poor LV washout and longer particle residence times,
consistent with poor LV unloading and compromised flow.
Imamura10 found that increasing HVAD pump body area in
the coronal x-ray plane was associated with a reduced decrement in LVEDD
and pulmonary capillary wedge pressure during ramp studies. Larger pump
area would correspond to a more laterally-oriented IFC.
In contrast, we did not find an association between malposition and
decrement in MR or LVEDD from pre- to post-LVAD. However, we had only
fixed-RPM echo studies. This MR finding is contrast to our previous
work, wherein greater total malposition magnitude predict a higher
degree of post-LVAD MR11. However, the studies differ
on a few key aspects: a) Pasrija included only patients with at least
mild-moderate preoperative MR; b) they used a subset of the current
population (only patients implanted 2013-2017; N = 41 vs 83 patients in
the current study); and c) MR was graded on a more granular scale, which
captured intermediate degrees such as mild-moderate. These differences
likely explain the discrepancy.
Imamura10 also found that a steeper coronal plane IFC
angle (≥ 76 deg) was associated with increased LVEDD and wedge pressure.
However, such an angle represents relatively extreme superior-wall
directed malposition, which was rare in our study (Figure 3). Imamura’s
report has only nine patients in this group and 27 total patients, so
their findings may not be translatable to a larger population.
This and other clinical studies of IFC malposition in
CF-LVADs10,12,13 rely on two-dimensional measurements
of IFC angle relative to the spine or horizontal in the coronal plane,
and are unable to identify septal or lateral-wall malposition.
We did find that IFC malposition was associated with readmissions
(HFRAs). Patients with total malposition magnitude > 40 deg
had an increased incidence of 30-day HFRAs, while patients with a
lateral plane angle ≤ -20 deg experienced an increased incidence of
overall HFRAs. Imamura associated a higher IFC coronal angle
(> 65 deg) with increased HFRAs in HVAD
patients10, while an angle > 28 deg was
the cut-off in a larger population with the Heartmate
312. It is unclear why the two devices have such
different thresholds, since both are intrapericardial with integral IFCs
of roughly the same diameter. In contrast, Shih et
al.13 found increased “malposition-related” adverse
event rates, including HFRAs, in patients with a Heartmate 3 whose
median spine-IFC angle on chest x-ray was 66 deg at one month, compared
to 59 deg in patients without adverse events. In this study, a
higher pump-spine angle would correspond to a shallower angle using the
method of Imamura.
Finally, we did not find an association between malposition and either
PT/eCVA or survival free of malposition-related surgery. PT and eCVA
have multifactorial causes, including hypertension and inadequate
antithrombotic therapy14,15. While we did observe an
association between malposition and pump thrombosis in the Heartmate II,
we observed deviations that were much more extreme than those observed
for the HVAD, and which tended to be primarily superior-wall and
septum-directed1. The degree of malposition observed
here may not be sufficient to independently cause thrombosis. Mortality
is similarly multifactorial.