Transthoracic Echocardiographic Assessment of Continuous-Flow Left Ventricular Assist Devices

Point-of-Care Ultrasound in the Evaluation of Patients with Left Ventricular Assist Devices at the Emergency Department

BACKGROUND

Left ventricular assist devices (LVADs) can be used as a bridging therapy for myocardial recovery or cardiac transplant, as well as a destination therapy for long-term support in patients with advanced heart failure. Patients with LVADs can present to the emergency department (ED) for acute deterioration and emergency physicians (EPs) must be equipped with the necessary knowledge and skill to treat this unique population.

OBJECTIVE

This review describes the role of point-of-care ultrasound (POCUS) in the evaluation of patients with LVADs and illustrates how EPs can incorporate POCUS into the evaluation of these patients in the ED.

DISCUSSION

The clinical applications for which POCUS may be useful in patients with LVADs include hypotension or shock, dyspnea, cardiac failure, dysrhythmia, syncope, and cardiac arrest. The normal features of POCUS in patients with LVADs and the features of POCUS associated with diseased states are presented.

CONCLUSIONS

Patients with LVADs have altered anatomy and physiology. Therefore, an understanding of key modifications to standard POCUS views is necessary so that EPs can use POCUS effectively in their evaluation of these patients.

Echocardiography for left ventricular assist device implantation and evaluation: an indispensable tool

Echocardiography is an indispensable tool in the evaluation, placement, management and follow-up of patients with left ventricular assist devices (LVAD). While transoesophageal echocardiography is the ideal tool in guiding the implantation procedure, transthoracic echocardiography is essential during the initial evaluation, patient selection and in the post-operative follow-up. This review attempts to summarize which parameters the echocardiographic assessment should focused on during each step. In particular, during the pre-operative assessment, it is of paramount importance to assess the presence of aortic regurgitation and most importantly to evaluate right ventricular function, since it is one of the strongest predictor of post-implant right ventricular failure. During the procedure, through transoesophageal echocardiography, it is possible to confirm the correct placement of the inflow cannula, to assess right ventricular function and to guide the choice of the right pump speed. Transthoracic echocardiographic is an essential part in the patient's follow-up once the LVAD has been implanted, in order to attest the onset of possible complications.

Cardiac computed tomography improves the identification of cardiomechanical complications among patients with suspected left ventricular assist device malfunction

BACKGROUND

Left ventricular assist devices (LVAD) are increasingly used for durable mechanical circulatory support in advanced heart failure. While LVAD therapy provides substantial improvement in mortality and quality of life, long-term therapy confers increased risk for device complications. We evaluated if cardiac computed tomography (CCT) improves the detection of cardiomechanical complications among patients with LVAD and suspected device malfunction.

METHODS

In this study, we compared the diagnostic performance of CCT and transthoracic echocardiography (TTE) for the identification of cardiomechanical LVAD complications, including thrombus or neointimal hyperplasia, inflow cannula malposition with dynamic obstruction, fixed outflow obstruction, device infection, and severe aortic regurgitation. Complications were confirmed with surgical evaluation, pathologic assessment, or response to therapeutic intervention.

RESULTS

Among 58 LVAD patients, who underwent CCT and TTE for suspected LVAD dysfunction, there were 49 confirmed cardiomechanical LVAD complications among 43 (74.1%) patients. The most common LVAD complication was thrombus or neointimal hyperplasia (65.3%), followed by dynamic obstruction (26.5%). Individually, CCT identified 29 of the 49 (59.2%) confirmed LVAD cardiomechanical complications, whereas TTE alone identified a complication in 11 cases (22.4%). However, diagnostic performance was greatest when the two modalities were used in combination, yielding a sensitivity of 67%, specificity of 93%, PPV of 97%, NPV of 47% and diagnostic accuracy of 73%.

CONCLUSION

The novel and complementary use of CCT with TTE for the evaluation of suspected device malfunction improves the accurate identification of cardiomechanical LVAD complication compared to either modality alone.

Right Ventricular Strain to Assess Early Right Heart Failure in the Left Ventricular Assist Device Candidate

PURPOSE OF REVIEW

Right heart failure (RHF) following left ventricular assist device implantation (LVAD) remains the primary cause of postoperative mortality and morbidity, and prediction of RHF is the main interest of the transplantation community. In this review, we outline the role and impact of right ventricular strain in the evaluation of the right ventricle function before LVAD implantation.

RECENT FINDINGS

Accumulating data suggest that measurement of right ventricular longitudinal strain (RVLS) has a critical role in predicting RHF preoperatively and may improve morbidity and mortality following LVAD implantation. However, the significant intraobserver, interobserver variability, the lack of multicenter, prospective studies, and the need for a learning curve remain the most critical limitations in the clinical practice at present. This review highlighted the importance of right ventricular strain in the diagnosis of RHF preoperatively and revealed that RVLS might have a crucial clinical measurement for the selection and management of LVAD patients in the future with the more extensive multicenter studies.

Contrast Microsphere Destruction by a Continuous Flow Ventricular Assist Device: An In Vitro Evaluation Using a Mock Circulation Loop

OBJECTIVES

Transthoracic echocardiography (TTE) is fundamental in managing patients supported with ventricular assist devices (VAD). However imaging can be difficult in these patients. Contrast improves image quality but they are hydrodynamically fragile agents. The aim was to assess contrast concentration following passage through a VAD utilising a mock circulation loop (MCL).

METHODS

Heartware continuous flow (CF) VAD was incorporated into a MCL. Definity® contrast was infused into the MCL with imaging before and after CF-VAD. 5 mm2 regions of interest were used to obtain signal intensity (decibels), as a surrogate of contrast concentration.

RESULTS

Four pump speeds revealed significant reduction in contrast signal intensity after CF-VAD compared to before CF-VAD (all p < 0.0001). Combined pre- and postpump data at all speeds showed a 22.2% absolute reduction in contrast signal intensity across the CF-VAD (14.8 ± 0.8 dB prepump versus 11.6 ± 1.4 dB postpump; p < 0.0001). Mean signal intensity reduction at each speed showed an inverse relationship between speed and relative reduction in signal intensity.

CONCLUSION

Contrast microsphere transit through a CF-VAD within a MCL resulted in significant reduction in signal intensity, consistent with destruction within the pump. This was evident at all CF-VAD pump speeds but relative signal drop was inversely proportional to pump speed.

[Rehabilitation standards for follow-up treatment and rehabilitation of patients with ventricular assist device (VAD)]

The increasing use of ventricular assist devices (VADs) in terminal heart failure patients provides new challenges to cardiac rehabilitation physicians. Structured cardiac rehabilitation strategies are still poorly implemented for this special patient group. Clear guidance and more evidence for optimal modalities are needed. Thereby, attention has to be paid to specific aspects, such as psychological and social support and education (e.g., device management, INR self-management, drive-line care, and medication).In Germany, the post-implant treatment and rehabilitation of VAD Patients working group was founded in 2012. This working group has developed clear recommendations for the rehabilitation of VAD patients according to the available literature. All facets of VAD patients' rehabilitation are covered. The present paper is unique in Europe and represents a milestone to overcome the heterogeneity of VAD patient rehabilitation.

Simulation of aortic valve dynamics during ventricular support

Existing commercially-used left ventricular assist devices (LVADs) make no attempt to automatically detect the aortic valve condition in their control methods to optimize ventricular assistance. An important design goal for LVADs is the ability to reliably and accurately detect aortic valve (AV) states during heart pump support that can cause harmful effects on AV structure and function. In this paper, we have investigated the correlation between AV performance and LVAD motor current as well as speed set points, simulating aortic valve blood flow, pressure, pump flow and LV mechanics using a simplified two-dimensional fluid-structure interaction finite-element model of AV dynamics.

Estimation of Left Ventricular Pressure with the Pump as “Sensor” in Patients with a Continuous Flow LVAD

Introduction

In long-term ventricular support of patients with LVADs, left ventricular pressure (plv is relevant for indicating the unloading level of the heart. Monitoring of plv over time might give more insight into the increase or decrease in native ventricular function. In this study, we aim to assess dynamic plv noninvasively, using the LVAD as a pressure sensor.

Methods

Pressure head (dplvad) was estimated from pump flow with a dynamic pump model ( 1 ). Estimated dplvad and measured aortic pressure were used to calculate left ventricular pressure. Moreover, parameters dp/dtmax and mean, minimum, and maximum plv were derived. The method was validated with a porcine ex vivo beating heart model by measurements conducted in 4 hearts supported with a Micromed DeBakey VAD and 3 hearts with a Heartmate II VAD. During each measurement, aortic and left ventricular pressure, pump flow, and pressure head were recorded for 30 s with a sampling frequency of 1 kHz.

Results

The estimation of left ventricular pressure appeared to be accurate for both pumps. The parameters mean and minimum pressure were estimated with high accuracy. The degree of accuracy of the estimated plv was proportional to the degree of accuracy of the dynamic pump model.

Conclusions

We proved that the LVAD model described in this paper can be used as a pressure indicator to determine LV pressure at any time based on noninvasive measurements of pump flow, aortic pressure, and the properties of the outlet graft.

Slope of the anterior mitral valve leaflet: a new measurement of left ventricular unloading for left ventricular assist devices and systolic dysfunction

Left ventricular assist device (LVAD)-supported patients are evaluated routinely with use of transthoracic echocardiography. Values of left ventricular unloading in this unique patient population are needed to evaluate LVAD function and assist in patient follow-up. We introduce a new M-mode measurement, the slope of the anterior mitral valve leaflet (SLAM), and compare its efficacy with that of other standard echocardiographically evaluated values for left ventricular loading, including E/e' and pulmonary artery systolic pressures. Average SLAM values were determined retrospectively for cohorts of random, non-LVAD patients with moderately to severely impaired left ventricular ejection fraction (LVEF) (<0.35, n=60). In addition, pre- and post-LVAD implantation echocardiographic images of 81 patients were reviewed. The average SLAM in patients with an LVEF <0.35 was 11.6 cm/s (95% confidence interval, 10.4-12.8); SLAM had a moderately strong correlation with E/e' in these patients. Implantation of LVADs significantly increased the SLAM from 7.3 ± 2.44 to 14.7 ± 5.01 cm/s (n=42, P <0.0001). The LVAD-supported patients readmitted for exacerbation of congestive heart failure exhibited decreased SLAM from 12 ± 3.93 to 7.3 ± 3.5 cm/s (n=6, P=0.041). In addition, a cutpoint of 10 cm/s distinguished random patients with LVEF <0.35 from those in end-stage congestive heart failure (pre-LVAD) with an 88% sensitivity and a 55% specificity. Evaluating ventricular unloading in LVAD patients remains challenging. Our novel M-mode value correlates with echocardiographic values of left ventricular filling in patients with moderate-to-severe systolic function and dynamically improves with the ventricular unloading of an LVAD.

Critical Care Transthoracic Echocardiography: Atrial Sinus Rhythm During Ventricular Fibrillation

A 70-year-old man with end-stage heart failure and a continuous-flow left ventricular assist device received repeated electrical discharges from his biventricular implantable cardiac defibrillator. Although the electrocardiogram demonstrated ventricular fibrillation, the patient was awake and in no distress. A focused transthoracic echocardiogram was performed to assess ventricular function revealing simultaneous atrial sinus rhythm and ventricular fibrillation. This clinical scenario highlights a unique clinical finding, the complexity of the care of continuous-flow left ventricular assist device patients, and the challenges of intensivist-performed bedside focused transthoracic echocardiogram.

A novel echocardiographic imaging technique, intracatheter echocardiography, to guide veno-venous extracorporeal membrane oxygenation cannulae placement in a validated ovine model

Background

Echocardiography plays a fundamental role in cannulae insertion and positioning for extracorporeal membrane oxygenation (ECMO). Optimal access and return cannulae orientation is required to prevent recirculation. The aim of this study was to compare a novel imaging technique, intracatheter echocardiography (iCATHe), with conventional intracardiac echocardiography (ICE) to guide placement of ECMO access and return venous cannulae.

Methods

Twenty sheep were commenced on veno-venous ECMO (VV ECMO). Access and return ECMO cannulae were positioned using an ICE-guided technique. Following the assessment of cannulae position, the ICE probe was then introduced inside the cannulae, noting location of the tip. After 24 h, the sheep were euthanized and cannulae position was determined at post mortem. The two-tailed McNemar test was used to compare iCATHe with ICE cannulae positioning.

Results

ICE and iCATHe imaging was possible in all 20 sheep commenced on ECMO. There was no significant difference between the two methods in assessing access cannula position (proportion correct for each 90%, incorrect 10%). However, there was a significant difference between ICE and iCATHe success rates for the return cannula (p = 0.001). Proportion correct for iCATHe and ICE was 80% and 15% respectively. iCATHe was 65% more successful (95% CI 27% to 75%) at predicting the placement of the return cannula. There were no complications related to the ICE or iCATHe imaging.

Conclusion

iCATHe is a safe and feasible imaging technique to guide real-time VV ECMO cannulae placement and improves accuracy of return cannula positioning compared to ICE.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-2-2) contains supplementary material, which is available to authorized users.

Assessment of myocardial viability and left ventricular function in patients supported by a left ventricular assist device

BACKGROUND

Chronically supported left ventricular assist device (LVAD) patients may be candidates for novel therapies aimed at promoting reverse remodeling and myocardial recovery. However, the effect of hemodynamic unloading with a LVAD on myocardial viability and LV function in chronically supported LVAD patients has not been fully characterized. We aimed to develop a non-invasive imaging protocol to serially quantify native cardiac structure, function, and myocardial viability while at reduced LVAD support.

METHODS

Clinically stable (n = 18) ambulatory patients (83% men, median age, 61 years) supported by a HeartMate II (Thoratec, Pleasanton, CA) LVAD (median durations of heart failure 4.6 years and LVAD support 7 months) were evaluated by echocardiography and technetium-99m ((99m)Tc)-sestamibi single photon emission computed tomography (SPECT) imaging at baseline and after an interval of 2 to 3 months. Echocardiographic measures of LV size and function, including speckle tracking-derived circumferential strain, were compared between ambulatory and reduced LVAD support at baseline and between baseline and follow-up at reduced LVAD support. The extent of myocardial viability by SPECT was compared between baseline and follow-up at reduced LVAD support.

RESULTS

With reduction in LVAD speeds (6,600 rpm; interquartile range: 6,200, 7,400 rpm), LV size increased, LV systolic function remained stable, and filling pressures nominally worsened. After a median 2.1 months, cardiac structure, function, and the extent of viable myocardium, globally and regionally, was unchanged on repeat imaging while at reduced LVAD speed.

CONCLUSIONS

In clinically stable chronically supported LVAD patients, intrinsic cardiac structure, function, and myocardial viability did not significantly change over the pre-specified time frame. Echocardiographic circumferential strain and (99m)Tc-sestamibi SPECT myocardial viability imaging may provide useful non-invasive end points for the assessment of cardiac structure and function, particularly for phase II studies of novel therapies aimed at promoting reverse remodeling and myocardial recovery in LVAD patients.

Medical management of patients with continuous-flow left ventricular assist devices

OPINION STATEMENT

The prevalence of patients living with advanced heart failure continues to rise. For a subset of these patients, continuous-flow left ventricular assist devices (LVADs) are a life-saving therapy. Given the efficacy and durability of contemporary LVAD devices, their use has increased exponentially in recent years. The medical management of patients with an LVAD is an area of expertise for advanced heart failure clinicians, but a general understanding of the initial approach to, and stabilization of, LVAD patients is an important skillset for many health care providers. The rapidly changing field of the medical management of LVAD patients is largely based on clinical experience and limited published data. In this manuscript, we integrate the available published data on the medical management of LVAD patients with the growing clinical experience.

Speckle tracking echocardiography as a new technique to evaluate right ventricular function in patients with left ventricular assist device therapy

BACKGROUND

Right ventricular (RV) systolic function has a critical role in determining the clinical outcome and the success of using left ventricular assist devices (LVADs) in patients with refractory heart failure. RV deformation analysis by speckle tracking echocardiography (STE) has recently allowed a deeper analysis of RV longitudinal function. The aim of the study was to observe RV function by STE in patients with advanced heart failure before and after LVAD implantation.

METHODS

Transthoracic echo Doppler was performed in 10 patients referred for LVAD therapy at baseline and with serial echocardiograms after LVAD implantation. In a sub-group of 4 patients, an echocardiographic evaluation was also made after intra-aortic balloon pump (IABP) support was initiated and before LVAD implantation. All echocardiographic images were analyzed off-line to calculate the free wall RV longitudinal strain (RVLS).

RESULTS

Three patients who presented the lowest free wall RVLS values at baseline, showed a progressive decline of RVLS after LVAD implant, presenting finally RV failure; however, patients with higher values of RVLS at baseline presented a further and overt increase of strain values in the course of follow-up. The overall performance for the prediction of RV failure after LVAD implant was greatest for free wall RVLS (area under the curve, 0.93). For the sub-group receiving the IABP as an intermediate step, only 2 patients with an increase of RVLS after IABP implantation also showed an increase of RVLS levels, after subsequent LVAD implantation. The 2 patients without an increase of RVLS after IABP implantation also presented with RV failure after LVAD therapy.

CONCLUSIONS

This study of 10 patients indicates that the new parameter of RVLS, representing RV myocardial deformation, may have important clinical implications for the selection and management of LVAD patients. A large multicenter study is required to confirm these observations and to quantify the clinical significance of changes in RVLS value.

Management of patients with implanted ventricular assist devices for noncardiac surgery: a clinical review

While originally primarily used as bridge to cardiac transplantation and bridge to recovery, more commonly ventricular assist devices (VADs) are being inserted as destination therapy. These patients are being discharged from transplant and mechanical assist centers, living as outpatients, and thus the pool of community-dwelling patients with VADs continues to expand. Not infrequently they present for surgical procedures either directly related to the device itself or more often incidental to the fact that they have a VAD. This scenario may be more common in patients with VADs placed for destination therapy because these patients tend to be older and have more comorbidities and are living longer with their device. Thus, it is important for all anesthesiologists to be aware of the special anesthesia needs of patients with VADs requiring noncardiac surgery.

Effects of the HeartMate II left ventricular assist device as observed by serial echocardiography

BACKGROUND

The HeartMate II is the most frequently used left ventricular assist device (LVAD) in patients with end-stage heart failure. There is a paucity of data regarding its longitudinal cardiac effects, particularly that on diastole.

METHODS

This retrospective study was an evaluation of echocardiograms preoperatively and at 3, 6, and 12 months postoperatively in patients with a HeartMate II. Measurements included left ventricle (LV) dimensions, ejection fraction (EF), right ventricle (RV) size and function, parameters of diastolic function, and an analysis of mitral regurgitation (MR), tricuspid regurgitation (TR), aortic insufficiency (AI), and aortic valve thickening.

RESULTS

Forty-seven patients were evaluated. LV dimensions decreased but EF, RV size, and RV function were unchanged. Right ventricular systolic pressure (RVSP) and diastolic parameters including mitral inflow E/A, deceleration time (DT), pulmonary vein inflow, left atrial size, and overall diastolic grade improved. LV relaxation measured by tissue Doppler (e') was unchanged and the E/e' ratio was also unchanged. Regarding valve function, MR decreased, TR was unchanged, and the aortic valve became increasingly thickened with increased AI severity.

CONCLUSIONS

The HeartMate II unloads the LV as shown by decreased LV size, decreased MR, reduced RVSP, and improved patterns of mitral inflow. However, neither systolic function nor diastolic relaxation improves in this cohort. RV size and function also remain unchanged. The aortic valve shows increased thickening and AI likely from valve leaflet fusion. These results provide detailed functional and hemodynamic information regarding the longitudinal effects of the HeartMate II.

Right ventricular longitudinal strain correlates well with right ventricular stroke work index in patients with advanced heart failure referred for heart transplantation

BACKGROUND

Right ventricular (RV) systolic function has a critical role in determining the clinical outcome and success of using left ventricular assist devices (LVADs) in patients with refractory heart failure. Tissue Doppler and M-mode measurements of tricuspid systolic motion (tricuspid S' and tricuspid annular plane systolic excursion [TAPSE]) are the most currently used methods for the quantification of RV longitudinal function; RV deformation analysis by speckle-tracking echocardiography (STE) has recently allowed the analysis of global RV longitudinal function. Using cardiac catheterization as the reference standard, this study aimed at exploring the correlation between RV longitudinal function by STE and RV stroke work index (RVSWI) in patients referred for cardiac transplantation.

METHODS AND RESULTS

Right-side heart catheterization and transthoracic echo Doppler were simultaneously performed in 41 patients referred for cardiac transplantation evaluation for advanced systolic heart failure. Thermodilution RV stroke volume and invasive pulmonary pressures were used to obtain RVSWI. RV longitudinal strain (RVLS) by STE was assessed averaging all segments in apical 4-chamber view (global RVLS) and by averaging RV free-wall segments (free-wall RVLS). Tricuspid S' and TAPSE were also calculated. No significant correlations were found for TAPSE or tricuspid S' with RVSWI (r = 0.14; r = 0.06; respectively). Close negative correlations between global RVLS and free-wall RVLS with the RVSWI were found (r = -0.75; r = -0.82; respectively; both P < .0001). Furthermore, free-wall RVLS demonstrated the highest diagnostic accuracy (area under the receiver operating characteristic (ROC) curve 0.90) and good sensitivity and specificity of 92% and 86%, respectively, to predict depressed RVSWI using a cutoff value of less than -11.8%.

CONCLUSIONS

In a group of patients referred for heart transplantation, TAPSE and tricuspid S' did not correlate with invasively obtained RVSWI. RV longitudinal deformation analysis by STE correlated well with RVSWI, providing a better estimation of RV systolic performance.