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Department of Critical Care Medicine and ECMO Unit, University Hospitals of Leicester National Health Service Trust, Glenfield Hospital, Leicester, United Kingdom
A range of devices now exist to provide temporary mechanical circulatory support (MCS) for the RV in the setting of cardiogenic shock, RV infarction, pulmonary hypertension, post-cardiac surgery, and left ventricular (LV) assist device implantation.
The decision to wean from MCS is dependent on the pertinent assessment of cardiac recovery. Both hemodynamic and echocardiographic parameters are used in conjunction with the evaluation of other major organ function, being cognizant not to view the heart in isolation.
Echocardiographic parameters suggesting LV recovery have been studied extensively, validated in further studies, and have been incorporated into weaning algorithms.
The “TIDE”-Algorithm for the weaning of patients with cardiogenic shock and temporary mechanical left ventricular support with impella devices. A cardiovascular physiology-based approach.
Typically, LV ejection fraction (EF) ≥25%, aortic velocity-time integral (VTI) ≥10 cm, and mitral annular systolic velocity ≥6 cm/s, with minimal MCS support, are predictive of a successful wean.
However, robust objective echocardiographic measures of RV recovery remain more elusive.
The complex geometry of the RV makes it more challenging to obtain accurate and reproducible quantification of its function using two-dimensional echocardiography. In addition, the RV remodels disparately to different pathophysiologic states,
Furthermore, when the variable loading and unloading conditions provided by different MCS devices are thrown into the mix, the ability to identify echocardiographic parameters to accurately predict successful weaning becomes problematic.
The RV may be divided into three functional regions: inflow area, apex, and outflow tract (OT) (Fig 1). The free wall of the RV is composed of two sets of muscle fibers, longitudinal and transverse, which facilitate contraction. The interventricular septum (IVS) contains oblique fibers that also contribute to RV systole. Global RV systolic function can be attributed to the following
Inward movement of the free wall, due to basal transverse fiber contraction.
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Longitudinal motion, pulling the tricuspid annulus toward apex, caused by both IVS and free wall longitudinal fiber shortening.
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RV outflow tract (RVOT) contraction, occurring late in systole.
Fig 1Three-dimensional echocardiographic reconstruction of the right ventricle showing the three functional regions: inflow (green), apex (red), and outflow tract (yellow).
Longitudinal shortening accounts for the majority of right ventricular contraction and improves after pulmonary vasodilator therapy in normal subjects and patients with pulmonary arterial hypertension.
This explains the validity of the echocardiographic measures of longitudinal RV systolic function, tricuspid annular plane systolic excursion (TAPSE), and tricuspid annular systolic velocity (S’), in representing global RV function, but also highlights the importance of “ventricular interdependence” and the role of the IVS.
Cardiac magnetic resonance imaging provides the gold-standard reference for RV volumes and RV ejection fraction (RVEF), but is impractical in the setting of MCS weaning.
Recommendations for cardiac chamber quantification by echocardiography in adults: An update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging.
Evaluation of the clinical utility of transesophageal echocardiography and invasive monitoring to assess right ventricular function during and after pulmonary endarterectomy.
Guidelines for the echocardiographic assessment of the right heart in adults: A report from the American Society of Echocardiography endorsed by the European Association of Echocardiography.
but only examines one area of the RV, loses accuracy in the presence of regional abnormalities, and is not a technique recommended by current guidelines,
Recommendations for cardiac chamber quantification by echocardiography in adults: An update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging.
Strain imaging shows promise because it avoids geometric assumptions, is less load-dependent, and reflects inherent myocardial contractility, but relies on precise positioning of the region of interest and does not necessarily correlate with RV stroke volume (Fig 2).
Evaluation of right ventricular systolic function after mitral valve repair: A two-dimensional Doppler, speckle-tracking, and three-dimensional echocardiographic study.
Feasibility of intraoperative three-dimensional transesophageal echocardiography in the evaluation of right ventricular volumes and function in patients undergoing cardiac surgery.
but RVEF is load-dependent, can be misleading in the presence of significant tricuspid valve regurgitation (TR), and may not detect subclinical RV dysfunction.
Recommendations for cardiac chamber quantification by echocardiography in adults: An update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging.
Fig 3Calculation of right ventricular volumes and ejection fraction using three-dimensional echocardiographic reconstruction of the right ventricle and automated technology.
Moreover, all of these methods are reliant upon the acquisition of good quality two-dimensional imaging without artifact hindrance, which may not always be possible when MCS devices are positioned in the chambers of the heart (Fig 4).
Fig 4Two-dimensional transesophageal echocardiography upper esophageal view, showing temporary right ventricular assist device outflow cannula in the pulmonary artery (red arrow), and with color-flow Doppler displaying flow.
The weaning of temporary MCS typically involves reducing the flows through the MCS device in a stepwise manner, while observing both echocardiographic and hemodynamic parameters to detect evidence of RV recovery. Most weaning protocols assess cardiac function at approximately 1 L/min MCS flow before concluding to either wean off altogether or reestablish MCS support.
Evidence to predict successful weaning of RV MCS is sparse. Several studies reporting the weaning of RV MCS failed to specify which echocardiographic measures were applied to determine suitability for weaning, used “visual assessment” of RV function, or did not define cut-off values if parameters were used.
The “TIDE”-Algorithm for the weaning of patients with cardiogenic shock and temporary mechanical left ventricular support with impella devices. A cardiovascular physiology-based approach.
were able to show “reduced RV dysfunction” in patients successfully weaned from venoarterial (VA) extracorporeal membrane oxygenation (ECMO), defined as having at least two of the following criteria: severe TR, basal RV end-diastolic diameter >35 mm, TAPSE <15 mm, S’ <10 cm/s, and “poor ejection fraction.” Anderson et al.
defined RV failure as TAPSE ≤14 mm, basal RV end-diastolic diameter >42 mm, or mid-RV end-diastolic diameter >35 mm, as inclusion criteria to receive an Impella RP (Abiomed, Danvers, MA), but only specified “improvement of RV contractility” as an indication for MCS weaning.
In 46 patients with refractory circulatory collapse supported with peripheral VA-ECMO, Huang et al.
Three-dimensional echocardiography-derived right ventricular ejection fraction correlates with success of decannulation and prognosis in patients stabilized by venoarterial extracorporeal life support.
were able to identify several RV echocardiographic parameters, with cut-off values, capable of predicting a successful wean from MCS: RVEF >24.6%, RVFAC >25.1%, and RV free-wall strain >10.9%. RVEF had the greatest area under the curve and also was associated with 30-day mortality. In addition, adequate imaging was feasible in most patients and both interobserver and intraobserver variability were high.
Contradictory to previous studies, both TAPSE and severity of TR failed to predict weaning success. In patients who required temporary RV MCS after LV assist device insertion Dandel et al.
formulated an estimate of RV functional reserve to anticipate the ability of the RV to adapt to an increase in load after MCS weaning: load adaptation index (LAIRV). LAIRV = (VTITR × RVEDlength) / RVEDarea, where a LAIRV value ≥18 indicated normal RV adaptability. Kim et al.
studied 92 patients with refractory cardiogenic shock, supported with peripheral VA-ECMO, and compared echocardiographic parameters at baseline ECMO support to those at 30-50% flows. With respect to RV function, only S’ >10% increase from baseline proved to be an independent predictor of successful ECMO weaning. This indicated that fewer load-dependent measures, such as S’, could be more appropriate in the setting of MCS, and that a trend in a parameter, rather than an exact cut-off value, may provide a more pragmatic approach.
Less dependent to loading conditions, TAPSE and S peak systolic tricuspid velocity are the 2 most robust indices to investigate right ventricular systolic function.
The limited evidence available and the disparity of findings lead us back to the age-old problem with echocardiographic assessment of the RV—each parameter has its advantages and limitations. Future research may need to focus on identifying predictive parameters specific to the MCS device, such as peripheral VA-ECMO, central VA-ECMO, Impella RP, ProtekDuo (Cardiac Assist Inc, Pittsburgh, PA), depending upon whether the pericardium previously had been opened, whether artifacts interfered with image acquisition, and the differing changes in loading conditions as the support was weaned. Furthermore, patients with isolated RV failure will behave differently from those with concurrent LV failure, due to the impact of “ventricular interdependence” and the role of the IVS, so different measures of RV recovery would be prudent for the two subsets of patients. Aortic VTI often is used as a surrogate for LV stroke volume and as a predictor for successful weaning of left-sided MCS. However, RVOT VTI and its Doppler envelope appear to have been overlooked in the setting of RV MCS, despite extensive research in the setting of pulmonary hypertension.
The RV no longer is the neglected ventricle and is much better understood, but there is still much more to comprehend, as Albert Einstein cautioned, “The more I learn, the more I realize how much I don't know.”
Financial Disclosures
The present work was performed without any direct or indirect financial support.
Declarations of Interest
All authors declare no competing interests.
References
Kaul TK
Fields BL.
Postoperative acute refractory right ventricular failure: Incidence, pathogenesis, management and prognosis.
The “TIDE”-Algorithm for the weaning of patients with cardiogenic shock and temporary mechanical left ventricular support with impella devices. A cardiovascular physiology-based approach.
Longitudinal shortening accounts for the majority of right ventricular contraction and improves after pulmonary vasodilator therapy in normal subjects and patients with pulmonary arterial hypertension.
Recommendations for cardiac chamber quantification by echocardiography in adults: An update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging.
Evaluation of the clinical utility of transesophageal echocardiography and invasive monitoring to assess right ventricular function during and after pulmonary endarterectomy.
Guidelines for the echocardiographic assessment of the right heart in adults: A report from the American Society of Echocardiography endorsed by the European Association of Echocardiography.
Evaluation of right ventricular systolic function after mitral valve repair: A two-dimensional Doppler, speckle-tracking, and three-dimensional echocardiographic study.
Feasibility of intraoperative three-dimensional transesophageal echocardiography in the evaluation of right ventricular volumes and function in patients undergoing cardiac surgery.
Three-dimensional echocardiography-derived right ventricular ejection fraction correlates with success of decannulation and prognosis in patients stabilized by venoarterial extracorporeal life support.
Less dependent to loading conditions, TAPSE and S peak systolic tricuspid velocity are the 2 most robust indices to investigate right ventricular systolic function.
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