Left Ventricular Assist Device Conditions Research Articles

Significance of Aortic Valve Insufficiency with Left Ventricular Assist Device: Duration and Regurgitant Flow in a Mock Loop Study

In patients with left ventricular assist device (LVAD), aortic valve insufficiency (AI) could occur in longer period during the cardiac cycle, throughout the diastolic and part of the isovolumetric phases. As the result, the current echocardiographic evaluation of AI grade may underestimate the degree of AI in LVAD patients, especially those with significant AI. In this study, we investigated the differences in AI duration and regurgitant volume before and during LVAD supports (Off and On LVAD) using a mock circulatory loop. All measurements were performed using a mock circulatory system with a dilated silicone LV model attached to a HeartMate II LVAD (Abbott Lab), and pressure and flow measured in the LV, LVAD, and aorta. Baseline condition was established as no LVAD condition (Off LVAD setting) which has 17% ejection fraction, 62 bpm heart rate and 65 mmHg systemic pressure. LVAD condition (On LVAD setting) at 8,800 rpm with same ejection fraction, heart rate and systemic resistance (90 mmHg systemic pressure) was established, followed by testing at three AI severity conditions. AI severity was defined as mild, moderate, or severe based on effective regurgitant orifice area. AI conditions were created with small 3-D printed stents, which were nonobstructive to forward flow, but prevented the leaflets from fully closing. AI durations and regurgitant volumes were determined from the calculated backward flow through the aortic valve. With the constant systemic resistance in the On LVAD setting at 8,800 rpm, duration of AI increased by 8.3 % (75 to 83.3%) with mild AI, 5.6% (77.8 to 83.3%) with moderate AI, and 5.6% (77.8 to 83.3%) with severe AI compared to the Off LVAD setting. With the constant systemic resistance in the On LVAD setting at 8,800 rpm, regurgitant volume of AI increased by 0.11 L/min (0.12 to 0.23 L/min, 92%) in mild AI, 0.03 L/min (0.53 to 0.56 L/min, 5.7%) in moderate AI and 0.08L/min (0.78 to 0.86 L/min, 10.3%) with severe AI compared to the Off LVAD setting. This mock loop study demonstrated that AI duration was longer and regurgitant volume through the aortic valve was greater during LVAD support compared to same AI degree before LVAD. This suggests that clinical burden of AI may be underestimated in patients with LVAD.

Theoretical Estimation of Cannulation Methods for Left Ventricular Assist Device Support as a Bridge to Recovery

Left ventricular assist device (LVAD) support under cannulation connected from the left atrium to the aorta (LA-AA) is used as a bridge to recovery in heart failure patients because it is non-invasive to ventricular muscle. However, it has serious problems, such as valve stenosis and blood thrombosis due to the low ejection fraction of the ventricle. We theoretically estimated the effect of the in-series cannulation, connected from ascending aorta to descending aorta (AA-DA), on ventricular unloading as an alternative to the LA-AA method. We developed a theoretical model of a LVAD-implanted cardiovascular system that included coronary circulation. Using this model, we compared hemodynamic responses according to various cannulation methods such as LA-AA, AA-DA, and a cannulation connected from the left ventricle to ascending aorta (LV-AA), under continuous and pulsatile LVAD supports. The AA-DA method provided 14% and 18% less left ventricular peak pressure than the LA-AA method under continuous and pulsatile LVAD conditions, respectively. The LA-AA method demonstrated higher coronary flow than AA-DA method. Therefore, the LA-AA method is more advantageous in increasing ventricular unloading whereas the AA-DA method is a better choice to increase coronary perfusion.

Analysis of the arterial blood pressure waveform during left ventricular nonpulsatile assistance in animal models.

When the rotary blood pump is used as a left ventricular assist device (LVAD), the arterial blood pressure waveform changes with the LVAD condition. Based on evidence from an in vitro study, the change of the arterial blood pressure waveform during left ventricular assistance was evaluated using animal models. After the left pleural cavity was opened through the fifth intercostal space under general anesthesia, a rotary blood pump was implanted as an LVAD into 6 healthy calves. The direct left carotid arterial blood pressure waveform was measured and recorded by an oscilloscope. The Fast Fourier Transform technique was utilized to analyze the arterial blood pressure waveform and calculate the pulsatility index (PI) and the pulse power index (PPI). Similar to the in vitro study, the PI and PPI decreased exponentially with the increase of the LVAD assist ratio. By using this analysis methodology, a physiologically effective ventricular assistance might be achieved.

Analysis of the arterial blood pressure waveform using Fast Fourier Transform technique during left ventricular nonpulsatile assistance: in vitro study.

The arterial blood pressure waveform is variable during left ventricular assistance. The aim of this study is to examine the correlation between the left ventricular assist device (LVAD) condition and the arterial blood pressure waveform in a fixed cardiac output condition using a mock circuit. This mock circulation loop was composed of an aortic compliance chamber, a left atrial compliance chamber, a pneumatic pulsatile pump as a native heart, and a rotary blood pump representing the LVAD with left atrial drainage. The Fast Fourier Transform technique was utilized to analyze the arterial blood pressure waveform and calculate the pulsatility index (PI) and the pulse power index (PPI). The PI and PPI decreased with the increase of the LVAD rotational speed, exponentially. There was a significant negative correlation between the PI, PPI, and the LVAD rotational speed, flow rate, and assist ratio. The best correlation was observed between the PPI and the assist ratio (r = 0.986). From this viewpoint, an ideal LVAD condition may be estimated from the pulsatility change of the arterial blood pressure waveform.

Feasibility of a tiny Gyro centrifugal pump as an implantable ventricular assist device.

The Gyro pumps were developed for long-term circulatory support. The first generation Gyro pump (C1E3) achieved 1 month paracorporeal circulatory support in chronic animal experiments; the second generation (PI702) implantable ventricular assist device (VAD) was successful for over 6 months. The objective of the next generation Gyro pump is for use as a long-term totally implantable VAD and for pediatric circulatory support. This tiny Gyro pump (KP101) was fabricated with the same design concept as the other Gyro pumps. The possibility of an implantable VAD was determined after performance and hemolysis test results were compared to those of the other Gyro pumps. The pump housing and impeller were fabricated from polycarbonate with an impeller diameter of 35 mm. The diameter and height of the pump housings are 52.3 mm and 29.9 mm, respectively. At this time, a DC brushless motor drives the KP101, which is the same as that for the C1E3. The pump performance was measured in 37% glycerin water at 37 degrees C. Hemolysis tests were performed utilizing a compact mock loop filled with fresh bovine blood in a left ventricular assist device (LVAD) condition at 37 degrees C. The KP101 achieved the LVAD conditions of 5 L/min and 100 mm Hg at 2,900 rpm; generated 10 L/min against 100 mm Hg at 3,200 rpm; 3 L/min against 90 mm Hg at 2,600 rpm; and 2 L/min against 80 mm Hg at 2,400 rpm. In addition, the pump efficiency during this experiment was 12.5%. The other Gyro pumps. that is, the C1E3, PI601, and PI701, in an LVAD condition require 1,600, 2,000, and 2,000 rpm, respectively. The KP101 produced a normalized index of hemolysis (NIH) value of 0.005 g/100 L. With regard to the NIH, the other Gyro pumps, namely the C1E3, PI601, and PI701 demonstrated 0.0007, 0.0028, and 0.004 g/100 L, respectively. The KP101 produced an acceptable pressure flow curve for a VAD. The NIH value was higher than that of other Gyro pumps, but is in an acceptable range.