CardioNerds (Amit Goyal and Daniel Ambinder) join Dr. Jaya Kanduri, Dr. Dan Lu, and Dr. Joe Wang from Weill Cornell Cardiology for Levain cookies in Central Park. The ECPR is provided by Dr. Harsimran Singh (Cardiology Program Director and Interventional Cardiologist with expertise in ACHD). Episode introduction by CardioNerds Clinical Trialist Dr. Jeremy Brooksbank.
We discuss a case of a 24-year-old female with a history of unicuspid aortic valve with associated aortopathy status post mechanical aortic valve replacement and Bentall procedure at age 16 presents with acute onset substernal chest pain and shortness of breath. She was found to have mechanical aortic valve obstruction and severe aortic regurgitation resulting in cardiogenic shock. Unfortunately, the shock quickly progressed to refractory cardiac arrest requiring mechanical support with VA-ECMO before valve debridement was performed in the operating room. The differential for mechanical prosthetic valve stenosis includes pannus, thrombus, or vegetation. She was eventually found to have thrombus obstructing the outflow tract and holding the mechanical leaflets open leading to torrential regurgitation. She underwent successful surgical debridement. We discuss unicuspid aortic valve and associated aortopathy, surgical considerations regarding AVR, diagnosis and management of prosthetic valve dysfunction, approach to cardiogenic shock and considerations around activating and managing VA-ECMO.
With this episode, the CardioNerds family warmly welcomes Weill Cornell Cardiology to the CardioNerds Healy Honor Roll. The CardioNerds Healy Honor Roll programs support and foster the the CardioNerds spirit and mission of democratizing cardiovascular education. Healy Honor Roll programs nominate fellows from their program who are highly motivated and are passionate about medical education. The Weill Cornell fellowship program director, Dr. Harsimran Singh has nominated Dr. Jaya Kanduri for this position.
Pearls – Mechanical Valve Thrombosis
(1) Unicuspid aortic valves present with aortic stenosis earlier in life. There can be concurrent aortic regurgitation and, like bicuspid aortic valves, unicuspids can be associated with aortopathy as well as other congenital anomalies.
(2) Prosthetic valve stenosis is assessed with different echocardiographic parameters than what we use for native valves. The differential for mechanical valve stenosis includes pannus, thrombus, or vegetation. Patient prosthesis mismatch may also lead to elevated gradients.
(3) VA-ECMO provides robust flow in the setting of cardiogenic shock as well as gas exchange. While this flow may improve end-organ perfusion, it also increases left ventricular afterload, thereby potentially worsening LV ischemia and impeding LV recovery. Elevated afterload may also decrease innate contractility and prevent aortic valve leaflets from opening. Therefore, if a patient with a mechanical valve is on VA-ECMO, ensuring valve opening to prevent valve (or ventricular) thrombosis is paramount.
(4) Venting is sometimes necessary to decrease the left ventricular end diastolic pressure from the high afterload imposed by VA-ECMO. A microaxial temporary LVAD (example – Impella device) directly unloads the left ventricle, but cannot be used in the setting of a mechanical aortic valve. TandemHeart is also a consideration (inflow cannula placed across the interatrial septum in the left atrium) to unload the LV, but does not improve flow across the aortic valve so can lead to thrombus if a mechanical valve is present. Intra-aortic balloon counterpulsation using an IABP can be used to decrease afterload on the native heart and increase coronary perfusion, but does not directly unload the left ventricle.
(5) Acute mechanical valve thrombosis can be managed with emergency surgery or with low dose fibrinolytic therapy. Surgery is preferable when operative risk is low and if there are contraindications to fibrinolytic therapy such as prior intracranial hemorrhage or active bleeding.
(6) VA-ECMO can be weaned by slowly decreasing flow rates and assessing native cardiac function, hemodynamic response, and end-organ perfusion with assessments including echocardiography and pulmonary artery catheterization.
Notes – Mechanical Valve Thrombosis
1. What is a unicuspid aortic valve?
- Unicuspid aortic valves (UAVs) are rare with an incidence of only 0.02%.
- There are two types of UAVs. Acommisural UAVs have a single cusp with a stenotic central orifice and rudimentary commissures that do not divide the valve (pin-hole shaped), and are usually complicated by severe stenosis in early childhood. Unicommisural UAVs are composed of a single cusp with a single commissural attachment to the aortic wall and an elongated orifice (slit-like orifice), which has a less aggressive course and is generally discovered in adulthood.
- Aortic stenosis is almost universal among UAVs, present with or without aortic regurgitation in 92% of cases. Some series have shown 14% of cases with concurrent aortopathy.
- UAVs may be associated with congenital abnormalities likes anomalous coronaries, PDA, VSD and coarctation.
2. How do we assess for aortic prosthetic valve stenosis?
- Assessment for mechanical valve stenosis involves different echocardiographic parameters than when evaluating a native valve. Doppler velocity index (DVI) is the dimensionless index with LVOT VTI/AV VTI, with severe stenosis suggested by a ratio of <0.25. Acceleration time (AT) is the time from onset to peak velocity of the continuous wave Doppler jet with severe stenosis suggested by >100msec (it takes longer to gush through a more stenotic valve). Effective orifice area (EOA) <0.8 suggests severe stenosis. A rounded symmetrical contour of the prosthetic valve VTI is more suggestive of severe stenosis, versus a triangular and early peaking jet.
- Acceptable ranges for prosthetic valve gradients are different from native valves due to intrinsically higher gradients, with mechanical being higher than bioprosthetic. In evaluating for prosthetic valve stenosis, we need to compare expected gradients for a given valve against those being measured. Evaluating trends over time is invaluable.
3. What are the percutaneous mechanical circulatory support options for cardiogenic shock?
- MCS options include counterpulsation using an IABP, microaxial temporary LVAD (like the Impella devie), TandemHeart, and VA-ECMO.
- The IABP improves diastolic coronary perfusion and systolic afterload reduction. However, there is only 0-1 L/min of flow provided, and no direct LV decompression.
- Microaxial temporary LVADs directly unload the LV with the flow pump placed across the aortic valve. These devices can provide 2-5L/min of flow depending on which device is used.
- The TandemHeart directly unloads the LV as well with an inflow cannula placed in the LA and outflow cannula placed in the femoral artery (requiring a transseptal puncture), and provides 2.5-5L/min of flow.
- VA-ECMO can provide up to 3-7L/min of flow.
4. What are unique considerations of mechanical support and VA-ECMO in the setting of a mechanical aortic valve?
- With a mechanical aortic valve, it is important for the valve leaflets open to prevent leaflet thrombosis. High afterload from the VA-ECMO circuit due to retrograde flow can prevent the aortic valve from opening, especially if myocardial contractility is already compromised. Therefore, special consideration needs to be given to the flow rate of the circuit and maintaining native LV output.
- Venting options are limited with a mechanical aortic valve. A device cannot be placed across the valve and so microaxial flow pumps are contraindicated. TandemHeart effectively decompresses the LV by sucking blood from the LA, but does not promote flow across the aortic valve and predisposes to thrombus formation. IABP is the ideal device in the setting of a mechanical aortic valve as flow through the aortic valve is promoted, however there is no direct decompression of the LV and efficacy may be limited.
5. What is the acute management of mechanical valve thrombosis?
- Mechanical valve thrombosis is managed acutely with emergent surgery or use of low dose fibrinolytic therapy.
- Surgery is preferable when surgical expertise is readily available, operative risk is low, and there are contraindications to fibrinolysis.
- Other reasons to prefer surgery include recurrent valve thrombosis, severe heart failure symptoms, large clot size (>0.8cm2), presence of LA thrombus or concomitant CAD in need of revascularization, presence of other valve disease, and presence of possible pannus (which would not respond to fibrinolysis).
6. What is the approach to weaning VA-ECMO?
- Assessment of echocardiographic features, hemodynamics, and end-organ perfusion is essential for a successful VA-ECMO wean. First a turndown of the circuit is performed where the ECMO flow is decreased in a protocolized fashion. This should reduce afterload and therefore increase LV contractile reserve, as well as increase preload with return of flow through the ventricles. With these changes, successful hemodynamic parameters to look for are stable cardiac index, central venous pressure, pulmonary arterial pressures, and systemic blood pressures. Successful echocardiographic parameters include an increase in LVEF >20-25%, aortic VTI ≥10 cm, lateral mitral annulus peak systolic velocity ≥6 cm/s, and a normal appearing RV with midline septum. Of note the risk of thrombosis increases with lower circuit flows, so particular attention must be given to anticoagulation during weaning.
- As antegrade flow through the native LV increases and retrograde through the VA-ECMO circuit decreases, beware of the north-south syndrome. This is caused by a mixing cloud of oxygenated blood from ECMO and potentially deoxygenated blood from the LV (if pulmonary gas exchange is compromised). As this mixing cloud progressively travels distally from the aortic root, it may predispose to coronary and then neurologic ischemia. We can monitor for this using ABGs obtained from the right arm. Stay tuned for more on this as part of the biventricular shock discussion as part of the CardioNerds Critical Care Cardiology Series.
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