In vivo fluid dynamics of the Ventura interatrial shunt device in patients with heart failure

Abstract

Aims: Interatrial shunts are under evaluation as a treatment for heart failure (HF); however, their in vivo flow performance has not been quantitatively studied. We aimed to investigate the fluid dynamics properties of the 0.51 cm orifice diameter Ventura shunt and assess its lumen integrity with serial transesophageal echocardiography (TEE).

Methods and results: Computational fluid dynamics (CFD) and bench flow tests were used to establish the flow-pressure relationship of the shunt. Open-label patients from the RELIEVE-HF trial underwent TEE at shunt implant and at 6 and 12 month follow-up. Shunt effective diameter (D_eff) was derived from the vena contracta, and flow was determined by the continuity equation. CFD and bench studies independently validated that the shunt's discharge coefficient was 0.88 to 0.89. The device was successfully implanted in all 97 enrolled patients; mean age was 70 ± 11 years, 97% were NYHA class III, and 51% had LVEF ≤40%. Patency was confirmed in all instances, except for one stenotic shunt at 6 months. D_eff remained unchanged from baseline at 12 months (0.47 ± 0.01 cm, P = 0.376), as did the trans-shunt mean pressure gradient (5.1 ± 3.9 mmHg, P = 0.316) and flow (1137 ± 463 mL/min, P = 0.384). TEE measured flow versus pressure closely correlated (R² ≥ 0.98) with a fluid dynamics model. At 12 months, the pulmonary/systemic flow Qp/Qs ratio was 1.22 ± 0.12.

Conclusions: When implanted in patients with advanced HF, this small interatrial shunt demonstrated predictable and durable patency and performance.

Keywords: Flow dynamics; Heart failure; Interatrial shunt; Transesophageal echocardiography.

Figure 1

Shunt device and computational flow dynamics (CFD) examples. (A) Anterior perspective rendering of study device showing the ePTFE encapsulated shunt. (B–E) CFD half shunt sections spatial distribution of gauge pressure, velocity, wall shear stress and vorticity during steady state flow at pressure differential of 10 mmHg.

Figure 2

Computational flow dynamics (CFD) and in vitro bench measurement of shunt device flow/pressure relationship. represents data from CFD simulations in blood and are bench measurements in saline. Error bars are standard deviations. Curved lines are respective fits to model haemodynamic equation (1) with R ² > 0.99 for each fit. $\mathrm{∆}\overline{\mathrm{P}}$, mean pressure gradient; Q, flow.

Figure 3

Central illustration: Transesophageal echocardiographic (TEE) images of a widely patent shunt. Images from 12 month follow‐up in a 67‐year‐old male with non‐ischaemic cardiomyopathy. Top: Colour Doppler short axis view showing shunt frame and locations of the vena contracta and frame neck diameter measurements. Mid: Continuous wave Doppler through the shunt with dotted line indicating mean velocity. Bottom: Measured fluid dynamics values. $\mathrm{∆}\overline{\mathrm{P}}$, mean interatrial pressure gradient; D_eff, effective diameter; D_frame, measured diameter of the frame neck; D_vc, diameter vena contracta; LA, left atrium; Q, trans‐shunt flow; RA, right atrium.

Figure 4

Colour Doppler stenotic and pseudo stenotic shunt case examples. Top left: Short axis view of shunt with severely stenotic lumen at 6 month follow‐up. Shunt is in the anterior septum and angulated towards the posterior wall of the aorta at lower right in location of foramen ovale. Top right: Short axis view of pseudo stenotic shunt lumen. Bottom: Table with measured values. $\mathrm{∆}\overline{\mathrm{P}}$, mean interatrial pressure gradient; D_frame, measured diameter of the frame neck; D_eff, effective diameter; D_vc, diameter vena contracta; Q, trans‐shunt flow.

Figure 5

In vivo shunt orifice dimensions over time. Graphs showing individual patient transesophageal echocardiographic (TEE) measurements of vena contracta, frame neck, and effective diameters at implant and at 6 and 12 month follow‐up. The stenotic threshold (red dashed line). Blue circles below this line indicate that the shunt orifice size was artifactually reduced due to non‐coaxial imaging (pseudo stenotic). The red triangle represents a single patient with a stenotic shunt at 6 month follow‐up. That patient exited the study upon receiving a left ventricular assist device (LVAD) at 8 months at which time the shunt was occluded. Mean ± standard deviation values are exclusive of stenotic shunt.

Figure 6

In vivo shunt flow/pressure relationship over time. Scatter plots showing transesophageal echocardiographic (TEE) measured shunt flow Q as a function of the mean interatrial pressure gradient $\mathrm{∆}\overline{\mathrm{P}}$ at implant and at 6 month and 12 month follow‐up. Top row: Q calculated using the vena contracta diameter (D_vc). Bottom row: Q calculated using the effective diameter (D_eff). Individual patient data (blue circles), with population means ± standard deviations (blue crosses with error bars). The red triangle represents a single patient with a stenotic shunt at 6 month follow‐up. Patient data are compared with the model derived from computational fluid dynamics simulation (black curves).