A . Calhoun et al .: J Extra Corpor Technol 2025 , 57 , 24 – 31 29
detect , may signify a missed opportunity for earlier intervention .
Of note , ECHO and hemodynamic markers of LVD are often directly related . For example , the presence of arterial pulsatility in the setting of VA-ECMO support implies AV opening . Additionally , the presence of LVOT VTI tracings on the echocardiogram suggests that the AV must be opening at least to some extent [ 2 , 43 ].
Non-invasive and invasive mechanical unloading strategies
Unloading strategies are undertaken to reduce the complications of LVD and are separated into non-invasive and invasive mechanical unloading strategies .
Non-invasive LV unloading strategies include the use of positive end-expiratory pressure , diuresis , afterload reduction with vasodilators , inotropes , and reducing ECMO flows to decrease afterload [ 5 ]. These strategies can be rapidly performed and are generally easily reversible . In the absence of clinical indicators of LVD , these low-risk strategies are generally attempted prior to the initiation of invasive mechanical unloading methods .
Invasive LV unloading strategies are generally undertaken in the presence of clinical indicators of LVD , or with the failure of non-invasive unloading strategies . Invasive unloading strategies include the use of intra-aortic balloon pump ( IABP ) counter pulsation , atrial septostomy , left atrial drainage cannula placement , left ventricular drainage cannula placement , percutaneous
transvalvular micro-axial pumps such as Impella Ò ( Abiomed , Danvers , MA , USA ), and percutaneous trans-aortic valve venting strategies ( such as transradial catheter drainage of the LV ) [ 2 , 3 , 5 ]. More novel techniques for LV mechanical unloading include left radial access to catheterize the LV and directly drain blood and LV apical dual lumen single cannula placement for direct LV drainage with aortic reinfusion [ 2 , 44 ]. Mechanical LV unloading is the definitive step in addressing clinical and subclinical LVD , though increased risks are present [ 7 , 45 ].
It is important to recognize that mechanical LV unloading strategies function in mechanistically different ways and to varying effects . For example , IABP counter pulsation functions by reducing LV afterload and improving coronary perfusion pressure but requires a sufficient degree of myocardial function to provide AV opening and LV unloading [ 2 , 46 ]. Left atrial drainage functions by decreasing left atrial pressure , resulting in reductions in pulmonary congestion and decreased LV preload but will not directly facilitate the passage of blood across the AV . Direct LV drainage via a cannula through the left superior pulmonary vein or by LV apical cannulation or a percutaneous approach , where a small drainage catheter is placed via wire guidance across the aortic valve draining directly to the ECMO circuit , reduces LV volume and pressure but also does not facilitate the passage of blood across the AV [ 3 ]. Finally , percutaneous transvalvular micro-axial pump placement decreases LV pressure and propels blood out of the LV even without the presence of underlying cardiac activity [ 2 , 5 ].
Venous access to perform atrial septostomy or left atrial cannula placement can damage any structure from the point of access to the left atrium with possible sequelae of bleeding , damage to major vascular structures , cardiac tamponade , and VA-ECMO circuit complications such as air entrainment . In the case of IABP or other arterial access , similar complications including limb ischemia , bleeding , aortic dissection , cardiac tamponade , and other damage to vascular or cardiac structures can occur . Other risks of additional mechanical support devices include infection , hemolysis , and renal failure .
Given the risks of invasive mechanical LV unloading strategies , establishing triggers or thresholds for their use is crucial . Triggers should also consider patient-specific factors . For example , patients with significant peripheral vascular disease may not be ideal candidates for arterial access methods of LV mechanical unloading and likely have improved risk profiles with the use of atrial septostomy or other transvenous strategies . Similarly , patients with mechanical AV replacement are not candidates for percutaneous transvalvular micro-axial pump placement . Improving patient outcomes may be facilitated by standardizing the definition of LVD and identifying indications and triggers for LV mechanical unloading .
Summary
Although multiple large retrospective reviews suggest a survival benefit when comparing mechanical LV unloading to no unloading ( without indications for unloading being known ), recent prospective randomized trials have not yet supported this finding [ 7 – 9 ]. Additionally , a recent large retrospective review of the national inpatient sample , suggested increased mortality in VA-ECMO patients undergoing mechanical unloading with percutaneous transvalvular micro-axial pump placement [ 45 ]. A lack of uniform criteria or specific strategies for LV unloading may partially explain the negative results of prospective randomized trials . For example , of the prospective randomized clinical trials with LV unloading triggers listed , there were no PAC-derived triggers for mechanical unloading [ 8 , 9 , 17 ]. Additionally , to date , prospective randomized trials of LV unloading have only involved the use of left atrial cannulation for drainage and not the other methods . While left atrial cannulation and drainage can reduce pulmonary edema , it is not the most common method of mechanical LV unloading and requires specific expertise to accomplish . Additionally , simple randomization to mechanical unloading versus no unloading without a more systematic method of assessing for LVD such as PAC-derived hemodynamic data is not a sufficiently refined approach to capture the patients most likely to benefit from the mechanical LV unloading . Specifically , a low LVOT VTI or a lack of ALPP could be due to acute hypovolemia from the initiation of ECMO or low afterload from an acute reduction of SVR . Similarly , without prior knowledge of baseline cardiac function , signs of ventricular dysfunction such as low ejection fraction may not be an indication for mechanical unloading in the presence of sufficient ALPP and acceptable PAC-derived filling pressures ( See Fig . 1 ).
Aside from the type of strategy , perhaps the most crucial future direction of research on LV mechanical unloading is elucidating a preclinical threshold ( such as a combination of PAC pressures and ALPP ) that results in an outcome benefit .