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PHILADELPHIA -- Meticulous positioning matters in reducing stroke risk after left ventricular assist device (LVAD) placement, according to a researcher here.

Two parameters of multi-detector cardiac CT imaging were found to be associated with stroke: LVAD outflow cannula angulation and diameter of anastomosis, reported Tanushree Agrawal, MD, of the Houston Methodist DeBakey Heart & Vascular Center.

Strokes were more likely when there was a more acute angle between the LVAD outflow cannula and the aortic root (45.9° vs 61.2° for patients who did not have strokes, P=0.042). As for the anastomosis, a smaller diameter did not bode well either (1.34 mm vs 1.52 mm, P=0.019), Agrawal's study showed during a moderated poster session at the Heart Failure Society of America annual meeting.

"In spite of excellent standardization in medical care protocols, we really lack a standard protocol for surgical techniques in terms of angulation and diameter of anastomosis," she said at the meeting.

"Therefore, it is imperative to optimize LVAD surgical implant techniques and device manufacturing to allow less acute angulation and larger anastomosis site of the outflow cannula," Agrawal and colleagues concluded.

The investigators started out with the hypothesis that some cannula positions create unfavorable hemodynamics that in turn may have an impact on platelet reactivity and thrombogenicity.

"Conceptually, the concept of angulation of the outflow cannula is important, and this has been studied before using computational models. The flow to the cerebral circulation does depend on the direction of the cannula and one could posit that it may create watershed areas that might predispose to cerebral ischemia," according to Mandeep Mehra, MD, of Brigham and Women's Hospital and Harvard Medical School in Boston.

"In the same way, the diameter discordance may play a role in shear stress and thrombogenicity," Mehra, who was not involved in the study, told MedPage Today.

In line with the stroke incidence reported from other studies, 12 out of 78 consecutive patients from Agrawal's institution had had a stroke (two hemorrhagic, the rest ischemic) within 1 year of LVAD surgery in 2011-2016. All had undergone cardiac CT either for LVAD-related complications or for routine surveillance.

The bulk of patients had received the HeartMate II LVAD (94.8%); there was one HeartWare HVAD and one HeartMate 3 implanted as well.

Average age of the cohort was 56 at implant; 73.1% were men. Investigators did not find any significant baseline differences between those who did and did not have a stroke.

Univariate analysis showed that an outflow angle cutoff of 43.5° (HR 0.97, 95% CI 0.94-1.00) and an anastomosis diameter no smaller than 1.5 mm (HR 0.06, 95% CI 0.01-0.66) were both tied to better stroke-free survival.

Such a small number of events from a relatively small series makes it difficult to do a multivariable analysis, and these are arbitrary thresholds, Mehra cautioned. "Furthermore there is a confounding by indication effect of the imaging procedure," he said.

Agrawal acknowledged the retrospective nature of the study and the predominant use of the older HeartMate II. "To be honest, it's hard to extrapolate the results from an axial-flow device to a centrifugal-flow device, which is the standard of care right now," she said.

However, she speculated that if not the angle, at least the diameter of anastomosis would be significant in these newer LVADs, given that the HeartWare HVAD in particular carries a higher risk of stroke and has the smallest anastomosis.

"With each new device, engineering improvements have led to better outcomes," commented Mark Slaughter, MD, of University of Louisville in Kentucky. "The latest device, the HeartMate 3, has significantly reduced the number strokes by changing the size of the gaps, reduced blood element trauma, and possibly the introduction of a device 'pulse.'"

"Similarly, the position of the inflow cannula and the outflow graft when optimized should have a potential benefit and reduction in the adverse interaction of the human biologic system and the device," said Slaughter, who was not involved in the study.

The present data could apply to newer devices, said Mehra, albeit with unclear relevance to clinicians and surgical technique for now.

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