Echocardiographic evaluation of patients with a left ventricular device

Use of gated cardiac computed tomography angiography in the assessment of left ventricular assist device dysfunction

The purpose of this study is to describe the utility and limitations of gated contrast-enhanced cardiac computed tomography angiography in assessing left ventricular assist device function. Computed tomography angiography (CTA) was used in 14 patients with left ventricular assist devices (LVADs) who had persistent heart failure symptoms, hemodynamic instability, or potential problems with LVAD flows. Retrospectively gated contrast-enhanced CTA was performed on 64-detector scanner, and the CTA images were postprocessed in multiple curved projections on TeraRecon workstation. This study describes the use of CTA to identify LVAD-related issues that altered clinical management and explores the role of CTA and other techniques in evaluating LVAD function. Six of 14 LVAD patients who demonstrated no abnormality on CTA remained stable with medical management. In the remaining eight patients, CTA was abnormal, including abnormalities specifically related to the LVAD cannula. As a result of findings detected by CTA, six patients underwent surgical intervention, including device exchange and heart transplant. Computed tomography angiography is a noninvasive method that enhances diagnostic evaluation of patients with suspected LVAD dysfunction and can lead to changes in patient management.

Perioperative echocardiographic examination for ventricular assist device implantation

Ventricular assist devices (VADs) are systems for mechanical circulatory support of the patient with severe heart failure. Perioperative transesophageal echocardiography is a major component of patient management, and important for surgical and anesthetic decision making. In this review we present the rationale and available data for a comprehensive echocardiographic assessment of patients receiving a VAD. In addition to the standard examination, device-specific pre-, intra-, and postoperative considerations are essential to the echocardiographic evaluation. These include: (a) the pre-VAD insertion examination of the heart and large vessels to exclude significant aortic regurgitation, tricuspid regurgitation, mitral stenosis, patent foramen ovale, or other cardiac abnormality that could lead to right-to-left shunt after left VAD placement, intracardiac thrombi, ventricular scars, pulmonic regurgitation, pulmonary hypertension, pulmonary embolism, and atherosclerotic disease in the ascending aorta; and to assess right ventricular function; and (b) the post-VAD insertion examination of the device and reassessment of the heart and large vessels. The examination of the device aims to confirm completeness of device and heart deairing, cannulas alignment and patency, and competency of device valves using two-dimensional, and color, continuous and pulsed wave Doppler modalities. The goal for the heart examination after implantation should be to exclude aortic regurgitation, or an uncovered right-to-left shunt; and to assess right ventricular function, left ventricular unloading, and the effect of device settings on global heart function. The variety of VAD models with different basic and operation principles requires specific echocardiographic assessment targeted to the characteristics of the implanted device.

Performance study on newly developed impellers for a left ventricular assist device

Our research develops a performance study on newly developed impellers for a left ventricular assist device. In order to analyze the hemodynamic characteristics of blood flow through the ventricular assist device, the CFX-TASCflow software is adopted to investigate the flow-field characteristics. The numerical results provide not only the flow characteristics for the overall field, but also the data of relationship for flow rate and pressure head. In the conceptual design process, hemodynamic study for an initial impeller design is presented first and a geometry change is recommended. Two design models are developed and the associated flow rate and pressure head performances are evaluated as well. According to design criteria, the most efficient design is the one with a smooth flow passage and with a low possibility for vortex generation. We suggest the superior design be chosen for further in vitro testing and be prepared for the new design generation. It has been shown that the design can provide a flow rate of 3.0 l/min with a pressure head of 127.09 mmHg. Both the flow rate and pressure head can meet requirements for the left ventricular assist device to work normally.

Left Ventricular Assist Device Malfunction

OBJECTIVES

A protocol using transthoracic echocardiography was designed to diagnose the common malfunctions of patients on chronic support with a left ventricular assist device (LVAD).

BACKGROUND

Mechanical circulatory support, primarily with a LVAD, is increasingly used for treatment of advanced heart failure as a bridge to transplant and for long-term treatment of heart failure. The LVAD dysfunction is a recognized complication. To date, no studies have defined the role of transthoracic echocardiography in evaluating long-term mechanical complications of chronic LVAD support.

METHODS

Transthoracic echocardiography was used in a protocol designed to detect the common types of mechanical malfunction. Patients were followed up with serial echocardiograms, and clinical validations were made with findings from a catheter-based protocol and inspection at the time of cardiac transplant or corrective surgery.

RESULTS

Thirty-two patients with 44 LVADs were followed up during a four-year period using this protocol that correctly identified 11 patients with inflow valve regurgitation, 2 with intermittent inflow conduit obstruction, 1 with severe kinking of the outflow graft, and 9 with new insufficiency of the native aortic valve.

CONCLUSIONS

As LVAD use for end-stage heart failure becomes widespread, and durations of support are extended, dysfunction will be increasingly prevalent. Transthoracic echocardiography provides a practical method to accurately identify the causes of mechanical dysfunction with patients on chronic LVAD support.

Evaluation of a patient with left ventricular assist device dysfunction

With the increasing number of LVAD recipients due to lack of donor availability and use of an LVAD as destination therapy, there will be a significant proportion of this population presenting with device related complications. Initial evaluation should be with TEE because conduit obstruction would be a significant complication, among others. As observed in this case report, it is sometimes difficult to noninvasively detect device malfunction, and even surgical exploration left questions unanswered. Echocardiography has been the principal modality used so far to assess the LVAD cannulas. More reliance on Doppler velocities and establishment of a normal range of values and flow profiles of the inflow and outflow cannulas are necessary. Baseline echocardiographic studies could be used for future comparisons. Fluoroscopy and selective angiography have also been reported to be helpful. We would also recommend measuring LV hemodynamics, which have not been previously described, as an additional mode of evaluation of this emerging problem. This case report demonstrates the need for additional noninvasive modalities for diagnosis of ventricular assist device malfunction.

Evaluation of cardiac function during left ventricular assist by a centrifugal blood pump

In this study, the effects on varying cardiac function during a left ventricular (LV) bypass from the apex to the descending aorta using a centrifugal blood pump were evaluated by analyzing the left ventricular pressure and the motor current of the centrifugal pump in a mock circulatory loop. Failing heart models (preload 15 mm Hg, afterload 40 mm Hg) and normal heart models (preload 5 mm Hg, afterload 100 mm Hg) were simulated by adjusting the contractility of the latex rubber left ventricle. In Study 1, the bypass flow rate, left ventricular pressure, aortic pressure, and motor current levels were measured in each model as the centrifugal pump rpm were increased from 1,000 to 1,500 to 2,000. In Study 2, the pump rpm were fixed at 1,300, 1,500, and 1,700, and at each rpm, the left ventricular peak pressure was increased from 40 to 140 mm Hg by steps of 20 mm Hg. The same measurements as in Study 1 were performed. In Study 1, the bypass flow rate and mean aortic pressure both increased with the increase in pump rpm while the mean left ventricular pressure decreased. In Study 2, a fairly good correlation between the left ventricular pressure and the motor current of the centrifugal pump was obtained. These results suggest that cardiac function as indicated by left ventricular pressure may be estimated from a motor current analysis of the centrifugal blood pump during left heart bypass.