Abstract
A percutaneous temporary aortic valve hemodynamic support catheter is a device that can conceptually maintain stable hemodynamics when significant structural damage occurs to the native aortic valve ensuing acute severe aortic insufficiency. Applications may include a bridge to surgery in active aortic valve endocarditis and an option to allow for diseased valve resection prior to transcatheter aortic valve replacement. An early prototype has undergone successful fundamental mathematical, bench and animal proof-of-concept studies. Design, concept and early data are presented and discussed.
1
Introduction
Isolated structural damage to the aortic valve can occur from endocarditis or deliberate removal prior to valve replacement. In transcatheter aortic valve replacement (TAVR), resection of the diseased valve prior to valve replacement has perceived advantages and has been proposed as a strategy . Contemporary hemodynamic support devices, including the intraaortic balloon pump, TandemHeart device (Cardiac Assist Inc, Pittsburgh, PA) and Impella (Abiomed Inc, Danvers, MA) all require a competent aortic valve to operate . The need for a hemodynamic support system to manage acute aortic insufficiency (AI) is apparent.
Search for the “temporary aortic valve” design began several decades ago; few models have been studied but none reached clinical application. The reasons are likely multifactorial mirroring the difficulties for the device to satisfy several essential design criteria: ability of the device to approximate hemodynamics of the native aortic valve, to maintain adequate cardiac output, to afford acceptable coronary perfusion, to allow for aortic valve intervention (resection, replacement), ease of insertion and retrievability percutaneously as needed based on hemodynamic stability.
A prototype of a new percutaneous temporary aortic valve (TAV) catheter (HOCOR) is designed with all of the above criteria in mind. Early mathematical, bench and animal proof-of-concept models are presented and discussed.
2
Brief summary of the temporary aortic valve prototype
The balloon-based TAV is designed with the intention of a hemodynamic support device capable of insertion and retrieval like a catheter on demand based on the severity of the acute AI. A series of parallel balloons are built at the tip of a guiding catheter; the balloons serve as the temporary aortic valve when inflated in the ascending aorta, while the guiding catheter can function as a conduit for aortic valve resection and replacement.
2.1
Theoretical concept and mathematical model
During TAV balloon inflation in the ascending aorta, the gaps between the balloons and the aortic wall will determine the effective aortic stenosis (eAS) and insufficiency (eAI) at the site of the TAV deployment ( Fig. 1 ). The degree of eAS and eAI can be controlled based on the balloon configurations (balloon number, size and shape) and counter-pulsations in synchrony with the cardiac cycle . Insignificant ranges of eAS and eAI can readily be established in the ascending aorta by the TAV to support significant acute AI that may result from native aortic valve damage. Hemodynamic stability can be restored. The gaps between the balloons and the aorta will also allow for coronary perfusion avoiding myocardial ischemia during TAV deployment. A simple 3-balloon TAV design was initially used for mathematical modeling ( Fig. 1 ); the calculated eAS and eAI fell within mild-to-moderate ranges and should be well tolerated by a subject with normal left ventricle when the native aortic valve is rendered nonfunctional. Subsequent mathematical models of various balloon configurations and counter-pulsations were also provided .
2.2
In vitro flow model
A flow apparatus, using a system of water tanks, clear polyvinyl chloride (PVC) tubings and electrically controlled valves, was constructed to model the pulsatile conditions of the ascending aorta with and without simulated AI as shown in Fig. 2 . The 3-balloon TAV prototype was created with standard peripheral angioplasty balloons and indeflator for inflation–deflation of the device ( Fig. 3 ). The TAV was sized, when inflated, to fit the inner dimensions of the PVC tubing such that the gap space between the balloons and the tubing would fall within a calculated range in accordance to the mathematical model . While the gaps could add a small amount of forward flow resistance (eAS) at the site of the TAV during systole, it would prevent massive regurgitation of fluid volume retrograde into the left ventricle during diastole (eAI). The gaps could theoretically allow for diastolic coronary perfusion in an animal subject.
The findings of the in vitro flow model of the TAV showed encouraging results of the device’s ability to improve the hemodynamics from flow conditions of simulated severe AI. Specifically in simulated AI, the TAV was shown to increase the distal diastolic pressure, to reduce the widened pulse pressure, to protect the left ventricle by lowering its diastolic pressure and to reduce the aortic regurgitant volume. The TAV’s systolic pressure gradient did not cause significant reduction in the forward flow (cardiac output). Table 1 summarizes the results of in vitro flow testing of the TAV .
| Mean (standard deviation) | No AI (Baseline) | With induced AI | p-Value ⁎ | ||
|---|---|---|---|---|---|
| (Baseline) | (Proximal TAV) | (Distal TAV) | |||
| Systolic pressure (mmHg) | 90.7 (1.2) | 91.0 (1.7) | 90.3 (2.1) | 87.7 (1.2) | 0.11 |
| Diastolic pressure (mmHg) | 22.3 (1.0) | 8.7 (1.5) | 7.3 (0.6) | 11.0 (1.0) | 0.01 ⁎⁎ 0.27 ⁎⁎⁎ |
| Regurgitant volume (l) | 0 | 5.5 (0.2) | 5.0 (0.2) | 5.0 (0.2) | 0.05 |
| Cardiac output (l min − 1 ) | 9.6 (0.1) | 8.2 (0.2) | 8.1 (0.2) | 8.1 (0.2) | 0.56 |
| Cycles (RPM) | 12 | 12 | 12 | 12 | |
⁎ p-values are calculated for the parameters with induced AI only.
⁎⁎ p-value of 0.01 is between proximal and distal TAV.
⁎⁎⁎ p-value of 0.27 is between the baseline with AI and proximal TAV.
2.3
Animal model
Porcine models of approximately 90 kg were used for the studies. A prototype was constructed using 3 standard peripheral angioplasty balloons, indeflator and a guiding catheter capable of delivering a self-expanding stent to ablate the native aortic valve to create acute severe AI ( Fig. 4 ). The procedure was performed entirely percutaneously, closed-chest. Hemodynamic parameters including concomitant ECG were recorded at baseline conditions, at acute severe AI after the aortic valve was ablated and at acute AI with TAV protection. Pressure measurements were obtained in the left ventricle, proximal and distal to the TAV as indicated in Fig. 5 .
The results of the animal studies were also encouraging. First, the guiding catheter was able to deliver a self-expanding stent to the aortic annulus and successfully ablate the valve. As a result of the stent ablation, acute severe AI ensued. There were significant drop in the aortic diastolic pressure, equalization of the left ventricular and aortic diastolic pressures, acute elevation of the left ventricular diastolic pressure, a widened aortic pulse pressure.
Furthermore, in the presence of induced acute AI, deployment of the TAV in the proximal aorta was able to significantly lower the left ventricular diastolic pressure, increase the distal aortic diastolic pressure and narrow the widened pulse pressure. There was a mild systolic pressure gradient across the TAV, which did not significantly affect the cardiac output.
No ischemic changes on the ECG was noted during the TAV deployment. Fig. 6 and Table 2 summarize the results of the animal studies .
