The Enabler Cannula Pump: A Novel Circulatory Support System

Background

The enabler circulatory support system is a catheter pump which expels blood from the left or right ventricular cavity and provides pulsatile flow in the ascending aorta or pulmonary artery. It is driven by a bedside installed pulsatile driving console. The device can easily be implanted by a minimal invasive approach, similar to the Hemopump.

Purpose

To demonstrate the hemodynamic performance of this new intracardiac support system.

Methods

In a series of 9 sheep, hemodynamic evolutions were recorded in various conditions of myocardial contractility (the non-failing, the moderately failing and the severely failing heart). Heart failure was induced by injection of microspheres in the coronary arteries.

Results

Introduction of the cannula through the aortic valve was feasible in all cases. Pump flow by the enabler was gradually increased to a maximum of 3.5 L/min. Diastolic (and mean) aortic blood pressure is significantly increased in the non-failing and moderately failing condition (counterpulsation mode). In heart failure, cardiac output is significantly increased by the pump (p<0.0001). A drop in left atrial pressure (indicating unloading) is achieved in all conditions but reaches significant levels only during heart failure (p=0.0068).

Conclusions

This new circulatory support system contributes to stabilization of the circulation in the presence of cardiac unloading. In heart failure it actually supports the circulation by increasing cardiac output and perfusion pressure.

Pre-Clinical Evaluation of a Novel, Pneumatic, Ventricular Assist Device (Medos® HIA-VAD®) under Pathophysiological Conditions

To evaluate a new cardiac assist system, the Medos® HIA-VAD®, we studied the effects of mechanical unloading on regional and global myocardial dysfunction. As a model for the regional temporary contractile dysfunction we chose an anesthetized, open chest preparation in sheep. We occluded the diagonal coronary artery for 15 minutes and reperfused for 90 minutes. Hemodynamic parameters and wall thickening were monitored. Unloading with the 60-ml Medos® HIA-VAD® was performed either during ischemia (group II) or during reperfusion (group III). The recovery of non-uniformity indicated by post-ejection wall thickening was significantly faster (p<0.05) in both groups if compared to the non-assisted group (group I) (all groups n=4). Recovery of systolic wall thickening in the postischemic region in group I was only 76±12%, while it was 103±11% and 92±11% in groups II and III, respectively (p<0.05). In a canine model of global left ventricular failure, we occluded the left anterior descending coronary artery for 20 min, and after 5 minutes of reperfusion, the circumflex artery for 45 min (group I, n=5). After 5 min of CX occlusion in group II we performed assisted circulation for 90 min with the 10-ml (n=5) and the 25-ml (n=5) Medos® HIA-VAD®. In group I, no dog survided, in group II, all survided 4 hours of reperfusion (n=10). Lactate at the end of the experiment was 1.1±0.9 mmol/L (10-ml) and 1.1±0.2 mmol/L (25-ml) (p>0.05 vs. base line). We conclude that the Medos® HIA-VAD® is a reliable assist device that enhances myocardial recovery and allows sufficient peripheral circulation in the case of cardiogenic shock.

Role of myocardial protection for coronary artery bypass grafting on the beating heart

BACKGROUND

Minimal invasive coronary artery bypass grafting is often performed on the warm, beating heart. This setting requires special measures for protection of the myocardium during acute regional ischemia under normothermic conditions.

METHODS

A first possibility to enhance the tolerance to ischemia during short episodes of coronary artery occlusion is based on a pharmacologic approach. A second possibility is mechanical unloading of the ischemic heart during and after regional ischemia.

RESULTS

To interfere with the ionic imbalances leading to necrosis, blockade of the Na(+)-H+ exchanges can be induced. It is shown that the selective Na(+)-H+ exchange inhibitor HOE 694 is able to prevent ischemic contracture in the experimental setting. Another pharmacologic approach is the use of endogenous adenosine accumulation in the ischemic myocardium. This can be achieved by the use of nucleoside transport inhibitors (lidoflazine or nitrobenzylthioinosine) having the ability to accumulate adenosine at the site of its production. Adenosine has a strong cardioprotective effect via adenosine A1 receptor stimulation and induces bradycardia by opening K+ channels and increasing the potassium current. It is also shown that left ventricular unloading by an axial flow pump (Hemopump) improves postischemic myocardial dysfunction (stunning) in an experimental model of short regional ischemia and reperfusion.

CONCLUSIONS

Further clinical investigation of both pharmacologic and mechanical techniques for cardioprotection during minimally invasive coronary artery bypass grafting is required.