Relationship of IFC Position to Preoperative Anatomy
We prospectively assessed anatomic variables that previously predicted
Heartmate II IFC malposition. These included LVEDD, BMI, LV apex-midline
distance, and LV apex-LVOT angle.
We did not find a relationship between LVEDD and malposition. A smaller
LVEDD was associated with mortality and stroke in
CF-LVADs6. We also found no association between
malposition and PT/eCVA or mortality, as discussed below. Additional
contributing factors beyond pump position likely explain this
relationship.
We also found no relationship between BMI and malposition. A large
INTERMACS registry study linked obesity with device malfunction and
thrombosis, as well as readmissions7. However, only
16.8% of patients in that study received a CF-LVAD. It is possible that
the smaller profile CF-LVADs makes them less sensitive to the effects of
abdominal obesity than Heartmate II, which requires a pre- or
intra-peritoneal pocket.
Both CT imaging measurements predicted malposition. A larger midline-LV
apex distance was associated with increasingly septal IFC deviation.
Additionally, a steeper LVOT angle predicted IFC deviation toward both
the inferior wall and lateral walls.
A larger midline-LV apex distance indicates a more laterally and
posteriorly displaced apex. This may increase the risk of malposition by
making it difficult to reach the “true” apex. This is exacerbated in
LTHS patients if the thoracotomy is not sufficiently lateral.
Additionally, in these patients, the heart often impinges on the
ribcage, so the pump can be displaced by the ribs at closure. By
contrast, a shorter midline-LV apex distance predicted increased
lateral-wall malposition. This measurement suggests an apex closer to
midline, where the anterior chest wall could push the pump medially at
closure.
A steeper LVOT angle indicates a more vertically-oriented heart. Since
the natural lie of the CF-LVAD is horizontal, inserting it an up-tilted
ventricle will tend to point it inferior to the apex-MV axis. The apex
in these heart also tend to be more medial, which could portend a
laterally displaced IFC by the mechanism discussed above.
Having become more cognizant of malposition risk, we routinely use
preoperative CTs to select the intercostal space and extent of incision
for LTHS procedures. We also obtain biplanar transesophageal echo
imaging both before and after the chest is closed, since a uniplanar
four-chamber view will miss inferior-wall malposition. We also have
found preliminary success in repositioning CF-LVADs via a thoracotomy by
pulling them inferiorly and securing them to a rib.