Novel Left Heart Catheterization Ramp Protocol to Guide Hemodynamic Optimization in Patients Supported With Left Ventricular Assist Device Therapy

Biventricular catheterization combined with pressure-volume loop monitoring provides insight into the dynamic effects of left ventricular assist devices ramp on right ventricular function

Ramp studies are utilized for speed optimization of continuous flow left ventricular assist devices (CF-LVADs). We here report the utility of combined left and right heart catheterization during a ramp study to ensure a comprehensive understanding of the hemodynamic implications on both ventricles. Pressure-volume loop (PV loop) monitoring uncovered compromised systolic and mildly compromised right ventricular function with increasing LVAD speeds, despite improvement in left ventricular unloading. These findings informed patient management and highlight the potential utility of PV loop monitoring as an adjunct to left and right heart catheterization during ramp studies of next-generation LVADs.

In-silico hemodynamic ramp testing of ventricular assist device implanted patients using acausal cardiovascular-VAD modeling

BACKGROUND

While cardiovascular system and mechanical circulatory support devices are efficiently model the effect of disease and assistance, they can also lend valuable insights into clinical procedures. This study demonstrates the use of a CVS-VAD model for an invasive procedure; hemodynamic ramp testing, in-silico.

METHODS

The CVS model is developed using validated models in literature, using Simscape™. An analytically derived pump model is calibrated for the HeartWare VAD. Dilated cardiomyopathy is used as an illustrative example of heart failure, and heart failure patients are created virtually by calibrating the model with requisite disease parameters obtained from published patient data. A clinically applied ramp study protocol is adopted whereby speed optimization is performed following clinically accepted hemodynamic normalization criteria. Trends in hemodynamic variables in response to pump speed increments are obtained. Optimal speed ranges are obtained for the three virtual patients based on target values of central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mean arterial pressure (MAP) for hemodynamic stabilization.

RESULTS

Appreciable speed changes in the mild case (300 rpm), slight changes in the moderate case (100 rpm), and no changes in the simulated severe case are possible.

CONCLUSION

The study demonstrates a novel application of cardiovascular modeling using an open-source acausal model, which can be potentially beneficial for medical education and research.

Pulsatile Pressure Delivery of Continuous-Flow Left Ventricular Assist Devices Is Markedly Reduced Relative to Heart Failure Patients

Although continuous-flow left ventricular assist devices (CF-LVADs) provide an augmentation in systemic perfusion, there is a scarcity of in vivo data regarding systemic pulsatility on support. Patients supported on CF-LVAD therapy (n = 71) who underwent combined left/right catheterization ramp study were included. Aortic pulsatility was defined by the pulsatile power index (PPI), which was also calculated in a cohort of high-output heart failure (HOHF, n = 66) and standard HF cohort (n = 44). PPI was drastically lower in CF-LVAD-supported patients with median PPI of 0.006 (interquartile range [IQR], 0.002-0.012) compared with PPI in the HF population at 0.09 (IQR, 0.06-0.17) or HOHF population at 0.25 (IQR, 0.13-0.37; p < 0.0001 among groups). With speed augmentation during ramp, PPI values fell quickly in patients with higher PPI at baseline. PPI correlated poorly with left ventricular ejection fraction (LVEF) in all groups. In CF-LVAD patients, there was a stronger correlation with LV dP/dt (r = 0.41; p = 0.001) than LVEF (r = 0.21; p = 0.08; pint < 0.001). CF-LVAD support is associated with a dramatic reduction in arterial pulsatility as measured by PPI relative to HOHF and HF cohorts and decreases with speed. Further work is needed to determine the applicability to the next generation of device therapy.

Physiology of Continuous-Flow Left Ventricular Assist Device Therapy

The expanding use of continuous-flow left ventricular assist devices (CF-LVADs) for end-stage heart failure warrants familiarity with the physiologic interaction of the device with the native circulation. Contemporary devices utilize predominantly centrifugal flow and, to a lesser extent, axial flow rotors that vary with respect to their intrinsic flow characteristics. Flow can be manipulated with adjustments to preload and afterload as in the native heart, and ascertainment of the predicted effects is provided by differential pressure-flow (H-Q) curves or loops. Valvular heart disease, especially aortic regurgitation, may significantly affect adequacy of mechanical support. In contrast, atrioventricular and ventriculoventricular timing is of less certain significance. Although beneficial effects of device therapy are typically seen due to enhanced distal perfusion, unloading of the left ventricle and atrium, and amelioration of secondary pulmonary hypertension, negative effects of CF-LVAD therapy on right ventricular filling and function, through right-sided loading and septal interaction, can make optimization challenging. Additionally, a lack of pulsatile energy provided by CF-LVAD therapy has physiologic consequences for end-organ function and may be responsible for a series of adverse effects. Rheological effects of intravascular pumps, especially shear stress exposure, result in platelet activation and hemolysis, which may result in both thrombotic and hemorrhagic consequences. Development of novel solutions for untoward device-circulatory interactions will facilitate hemodynamic support while mitigating adverse events. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.

Left Ventricular Hemodynamics and Relationship with Myocardial Recovery and Optimization in Patients Supported on CF-LVAD Therapy

BACKGROUND

Despite interest in left ventricular (LV) recovery, there is an absence of data on the relationship between intrinsic LV hemodynamics and both reverse remodeling on continuous flow left ventricular assist device (CF-LVAD) therapy. We hypothesized that markers of intrinsic LV function would be associated with remodeling, optimization, and outcomes.

METHODS

Patients with continuous flow LVADs between 2015 and 2019 who underwent combined left and right heart catheterization (LHC/RHC) ramp protocol at a single institution were enrolled. Patients were stratified by response to CF-LVAD therapy: full responders (FR), partial responders (PR), or non-responders (NR) per Utah-Inova criteria. Hemodynamic data, including LV hemodynamics of peak LV dP/dt and tau (τ) were obtained at each phase. One-year heart failure hospitalization-free survival was the primary endpoint.

RESULTS

Among 61 patients included in the current study 38 (62%) were classified as NR, 14 (23%) PR, and 9 (15%) FR. Baseline LV dP/dt and τ varied by response status (P≤.02) and generally correlated with reverse remodeling on linear regression. Biventricular filling pressures varied with τ and there was an interaction effect of speed on the relationship between τ and PCWP (P=.04). Lastly, τ was a prognostic marker and associated with one-year HF-hospital free survival (OR 1.04, 95%CI 1.00-1.07, P=.02 per ms increase).

CONCLUSIONS

Significant correlations between τ and LV dP/dt and reverse remodeling were noted with tau serving as a prognostic marker. Higher LVAD speed was associated with a greater reliance on LVAD for unloading. Future work should focus on defining the optimal level of LVAD support in relation to LV recovery.

Clinical findings associated with incomplete hemodynamic left ventricular unloading in patients with a left ventricular assist device

INTRODUCTION AND OBJECTIVES

The effect of a centrifugal continuous-flow left ventricular assist device (cfLVAD) on hemodynamic left ventricular unloading (HLVU) and the clinical conditions that interfere with hemodynamic optimization are not well defined.

METHODS

We retrospectively evaluated the likelihood of incomplete HLVU, defined as high pulmonary capillary wedge pressure (hPCWP)> 15mmHg in 104 ambulatory cfLVAD patients when the current standard recommendations for cfLVAD rotor speed setting were applied. We also evaluated the ability of clinical, hemodynamic and echocardiographic variables to predict hPCWP in ambulatory cfLVAD patients.

RESULTS

Twenty-eight percent of the patients showed hPCWP. The variables associated with a higher risk of hPCWP were age, central venous pressure, absence of treatment with renin-angiotensin-aldosterone system inhibitors, and brain natriuretic peptide levels. Patients with optimal HLVU had a 15.2±14.7% decrease in postoperative indexed left ventricular end-diastolic diameter compared with 8.9±11.8% in the group with hPCWP (P=.041). Independent predictors of hPCWP included brain natriuretic peptide and age. Brain natriuretic peptide <300 pg/mL predicted freedom from hPCWP with a negative predictive value of 86% (P <.0001).

CONCLUSIONS

An optimal HLVU can be achieved in up to 72% of the ambulatory cfLVAD patients when the current standard recommendations for rotor speed setting are applied. Age, central venous pressure and therapy with renin-angiotensin-aldosteron system inhibitors had a substantial effect on achieving this goal. Brain natriuretic peptide levels and the magnitude of reverse left ventricular remodeling seem to be useful noninvasive tools to evaluate HLVU in patients with functioning cfLVAD.

Correction of High Afterload Improves Low Cardiac Output in Patients Supported on Left Ventricular Assist Device Therapy

There is a paucity of data describing the invasive assessment of afterload and influence on cardiac output in patients supported on left ventricular assist device (LVAD) therapy. From 2015 to 2018, patients on LVAD therapy were evaluated with simultaneous left/right heart catheterization ramp study for speed optimization. Hemodynamic parameters from 31 patients without significant aortic insufficiency were analyzed. Mean central aortic pressure (MAP) was elevated at 87 ± 13 mm Hg at baseline. No direct association between MAP and cardiac index (CI) was found (r = 0.11, p = 0.20). However, variable MAP provided vastly different patterns of cardiac output response to speed increments (positive correlation, p = 0.047 for MAP <80 mm Hg; negative trend, p = 0.25 for MAP > 100 mm Hg). Patients noted to be hypertensive (MAP > 90, n = 8) received nitrate therapy and experienced both improvement in biventricular filling pressures and a mean increase in CI from 2.4 to 2.9 L/min/m2 (+22%, p = 0.04) at a fixed revolutions per minute. High afterload is common in patients on LVAD therapy, is associated with poor response to ramp, and is ameliorated by nitrates. These findings serve as a foundation to evaluate the dynamic effects of high afterload and chronic vasodilator therapy in patients with durable LVADs.

Predicting the Risk of Right Ventricular Failure in Patients Undergoing Left Ventricular Assist Device Implantation

Background:

Right ventricular failure (RVF) is a cause of major morbidity and mortality after left ventricular assist device (LVAD) implantation. It is, therefore, integral to identify patients who may benefit from biventricular support early post-LVAD implantation. Our objective was to explore the performance of risk prediction models for RVF in adult patients undergoing LVAD implantation.

Methods:

A systematic search was performed on Medline, Embase, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews from inception until August 2019 for all relevant studies. Performance was assessed by discrimination (via C statistic) and calibration if reported. Study quality was assessed using the Prediction Model Risk of Bias Assessment Tool criteria.

Results:

After reviewing 3878 citations, 25 studies were included, featuring 20 distinctly derived models. Five models were derived from large multicenter cohorts: the European Registry for Patients With Mechanical Circulatory Support, Interagency Registry for Mechanically Assisted Circulatory Support, Kormos, Pittsburgh Bayesian, and Mechanical Circulatory Support Research Network RVF models. Seventeen studies (68%) were conducted in cohorts implanted with continuous-flow LVADs exclusively. The definition of RVF as an outcome was heterogenous among models. Seven derived models (28%) were validated in at least 2 cohorts, reporting limited discrimination (C-statistic range, 0.53–0.65). Calibration was reported in only 3 studies and was variable.

Conclusions:

Existing RVF prediction models exhibit heterogeneous derivation and validation methodologies, varying definitions of RVF, and are mostly derived from single centers. Validation studies of these prediction models demonstrate poor-to-modest discrimination. Newer models are derived in cohorts implanted with continuous-flow LVADs exclusively and exhibit modest discrimination. Derivation of enhanced discriminatory models and their validations in multicenter cohorts is needed.

Inadequate left ventricular unloading during ramp is associated with hospitalization or death during left ventricular assist device support

A combined right and left-sided heart catheterization (RHC/LHC) protocol was recently reported to optimize patients supported by left ventricular assist device (LVAD). Using this platform, we sought to evaluate the prognostic significance of several hemodynamic indices, including left ventricular end-diastolic pressure (LVEDP) and transaortic gradient (peak aortic pressure - peak left ventricular pressure in systole, TAG). We evaluated all patients undergoing RHC/LHC at our institution from 2015 through 2018, and comprehensive clinical data were obtained. Primary end points were (1) a composite outcome that included hospitalization or death and (2) 1-year overall survival after catheterization. Forty-two patients were included in the analysis. Optimization resulted in normalization of hemodynamic parameters; all variables were significantly improved from baseline (P ≤ .05). On univariate modeling, final LVEDP was associated with the primary end point (hazard ratio [HR], 1.2 per 1-mm Hg increase; 95% CI, 1.1-1.3; P = .002). After adjusting for LVAD speed, TAG, and cardiac index in a multivariate model, the association between LVEDP and the composite end point remained significant (HR, 1.2 per 1-mm Hg increase; 95% CI, 1.1-1.4; P = .001). In the setting of LVAD support, inadequate LV unloading was a significant marker of poor outcomes with time, suggesting that LVEDP is a central prognostic marker in this population.

Physiology of the Assisted Circulation in Cardiogenic Shock: A State-of-the-Art Perspective

Mechanical circulatory support (MCS) has made rapid progress over the last 3 decades. This was driven by the need to develop acute and chronic circulatory support as well as by the limited organ availability for heart transplantation. The growth of MCS was also driven by the use of extracorporeal membrane oxygenation (ECMO) after the worldwide H1N1 influenza outbreak of 2009. The majority of mechanical pumps (ECMO and left ventricular assist devices) are currently based on continuous flow pump design. It is interesting to note that in the current era, we have reverted from the mammalian pulsatile heart back to the continuous flow pumps seen in our simple multicellular ancestors. This review will highlight key physiological concepts of the assisted circulation from its effects on cardiac dynamic to principles of cardiopulmonary fitness. We will also examine the physiological principles of the ECMO-assisted circulation, anticoagulation, and the haemocompatibility challenges that arise when the blood is exposed to a foreign mechanical circuit. Finally, we conclude with a perspective on smart design for future development of devices used for MCS.

Novel Left Heart Catheterization Ramp Protocol to Guide Hemodynamic Optimization in Patients Supported With Left Ventricular Assist Device Therapy

Background Left ventricular (LV) hemodynamic assessment has been sparsely performed in patients supported on continuous-flow LV assist devices (cf LVADs ). Insight into dynamic changes of left heart parameters during ramp studies may improve LV assist device optimization and evaluate pathology. Methods and Results To complement right heart catheterization, a novel technique for left heart catheterization in patients with a cf LVAD was developed. Patients implanted with cf LVAD s underwent hemodynamic ramp left heart catheterization and right heart catheterization with transthoracic echocardiography. Continuous aortic and LV pressures were measured along with right atrial, pulmonary artery, and pulmonary capillary wedge pressures. A novel index, the transaortic gradient ( TAG ) was established. Thirty eight patients with cf LVADs were evaluated at a median of 446 days (interquartile range, 183-742) after device implant. During left heart catheterization performed for hemodynamic optimization, drop-in LV end-diastolic pressure and pulmonary capillary wedge pressure were associated with a rise in TAG . A range was identified for TAG (20-40 mm Hg) as providing the most optimal level of hemodynamic offloading. Pathologic states deviated from normal responses to ramp. LV assist device thrombosis was associated with an inability to increase in TAG during speed ramp. Significant aortic insufficiency was associated with a marked increase in LV end-diastolic pressure despite a concomitant decrease in pulmonary capillary wedge pressure with increasing LV assist device speeds. Conclusions Inclusion of left heart catheterization to a typical right heart catheterization LV assist device ramp protocol imparted unique insights to optimize cf LVAD speeds in different clinical scenarios. A novel index, the TAG was defined and provided additional resolution to optimized offloading.

Left Ventricular Assist Devices (LVADS): History, Clinical Application and Complications

Congestive heart failure is a major cause of morbidity and mortality as well as a major health care cost in the developed world. Despite the introduction of highly effective heart failure medical therapies and simple devices such as cardiac resynchronization therapy that reduce mortality, improve cardiac function and quality of life, there remains a large number of patients who do not respond to these therapies or whose heart failure progresses despite optimal therapy. For these patients, cardiac transplantation is an option but is limited by donor availability as well as co-morbidities which may limit survival post-transplant. For these patients, left ventricular assist devices (LVADs) offer an alternative that can improve survival as well as exercise tolerance and quality of life. These devices have continued to improve as technology has improved with substantially improved durability of the devices and fewer post-implant complications. Pump thrombosis, stroke, gastrointestinal bleeding and arrhythmias post-implant have become less common with the newest devices, making destination therapy where ventricular assist device are implanted permanently in patients with advanced heart failure, a reality and an appropriate option for many patients. This may offer an opportunity for long term survival in many patients. As the first of the totally implantable devices are introduced and go to clinical trials, LVADs may be introduced that may truly be alternatives to cardiac transplantation in selected patients. Post-implant right ventricular failure remains a significant complication and better ways to identify patients at risk as well as to manage this complication must be developed.