By Katrina Augustin MD, BSN-RN

Peer Reviewed by Randi Connor-Schuler MD

Case: 82 yo male with PMHX of DM, HTN, and HLD presenting via EMS after a syncopal episode. Patient reports recent recurrent angina and dyspnea that has been worsening over several months. Reports recent GI symptoms with N/V and subsequent syncopal episode today. Hypotensive on arrival. Exam notable for high pitched mid-systolic ejection murmur at right upper sternal border, EKG with LVH, and CXR with evidence of AV calcification.

Another case of CARDIOGENIC SHOCK…and after ruling out other common etiologies such as

…you are left with another case of valvular heart disease! Since acute regurgitant lesions were already discussed in episode CV-EMCrit 321, this post will focus on critical valvular stenosis, specifically critical aortic stenosis (AS).  AS is one of the most common forms of valvular heart disease with increasing prevalence with age (0.2% in 50s to 9.8% in octogenarians) (PMID: 33914604).

AS is classically a progressive chronic disease.…SO WHY SHOULD I CARE? I thought our focus was on ACUTE LIFE-THREATENING cardiac conditions! IT IS!

AS without intervention can deteriorate to acute decompensated heart failure and cardiogenic shock due to either progressive valve and myocardial dysfunction or perhaps even more frequently, a superimposed disease process. Life expectancy is only 1-2 years after the development of symptoms of LV failure with only an 18% survival to 5 years (PMID: 32314662).

This post will cover critical aortic stenosis

• Mechanism & Etiology
• Pathophysiology
• Signs & Symptoms
• Echocardiographic Definition of Severe AS
• Diagnosis
• Management

Remember when assessing a patient with valvular heart disease ALWAYS ASK…Is the patient SICK BECAUSE of a valvular lesion, or SICK WITH an existing valvular lesion?

…meaning

Can I explain my patients shock and decompensation on a worsening valvular lesion like severe aortic stenosis, OR does my patient have a chronic AS with a superimposed systemic illness causing their acute decompensation?

This is important because treatment is different.  Valvular disease causing CS, as discussed on previous post, requires targeted medical stabilization often with the addition of mechanical circulatory support (MCS) and early expert consultation for definitive surgical or interventional treatment; while patients with decompensation of their chronic valvular heart disease in the setting of a systemic illness need therapy targeted at the underlying systemic process often leading to resolution of their acute presentation (PMID: 32314662).

Critical Aortic Stenosis (AS)

Mechanism and Etiology:

Why is there an “obstruction” to blood flow from the left ventricle to the aorta?

This post will focus primarily on valvular stenosis (most common etiology) as supravalvular and subvalvular (subaortic) AS are rare etiologies beyond the scope of this post.

Degenerative tricuspid AS is associated with long standing stress on the valve with inflammatory changes, similar to atherosclerosis, leading to significant calcification and subsequent aortic valve orifice narrowing. Typically presents in 6th-8th decade of life. Often have co-existing coronary artery disease.

Degenerative Bicuspid aortic valve (BAV) frequently occurs by midlife due to increased stresses on the valve in setting of aberrant valve morphology. BAV is present in 1-2% of the population (PMID: 18296454). BAV is associated with an increased risk of endocarditis, aortic aneurysm, dissection, and aortic rupture.

Rheumatic heart disease causing AS is less common in the developed world but typically occurs in conjunction with mitral valve disease when it occurs. It is marked by commissural fusion rather than calcification as seen in degenerative AS. Prosthetic valve thrombosis is a rare etiology of AS but important to consider in patients with a history of valve replacement.

(PMID: 33914604).

Figure 1: A) Video clip illustrating severely calcified, stenotic aortic valve with limited valve leaflet mobility B) Color flow doppler demonstrating turbulent, high-velocity flow or “aliasing” through the severely stenotic AV orifice, clip courtesy of Randi Connor-Schuler MD

Pathophysiology:

PMID: 33914604

In a normal cardiac cycle, left ventricular (LV) pressure increases till it reaches aortic pressure, the AV then opens with ejection of blood and the LV and aortic pressures are relatively identical. When pressure in LV falls below aortic pressure the AV closes ending systole. In AS there is a small stenotic orifice (think pin hole in cap), thus the LV needs to exert more pressure to eject blood through valve leading to transvalvular gradient with LV pressure higher than aortic pressure (aortic pressure + transvalvular gradient=LV pressure).

The stenotic orifice creates a fixed obstruction thus increasing LV afterload or “wall stress.” To maintain stroke volume and cardiac output, the LV compensates by hypertrophying (increasing muscle mass) according to the Law of Laplace.

With time, progressive LV hypertrophy to compensate for worsening AS can become maladaptive leading to decreased compliance with impaired diastolic function and LV wall fibrosis that can cause systolic dysfunction and subsequent clinical decompensation (PMID: 33914604).

This excessive hypertrophy with impaired diastolic filling makes patients with critical AS very preload dependent and they will often require higher filling pressures to maintain adequate preload. Eventual pressure overload leads to LV remodeling placing patients at risk for secondary mitral regurgitation (think remodeled ventricle preventing MV leaflets from touching or “coapting”), elevated PCWP, and even post-capillary pulmonary hypertension (Type II pHTN) and right ventricular dysfunction making these patients especially challenging to manage. It is always important to always assess for other co-existing valvular pathology and right sided dysfunction in these patients.

Signs & Symptoms:

Compensatory LV hypertrophy in AS causes impaired diastolic function and a decreased reserve in coronary perfusion leading to THE CLASSIC symptoms of severe AS which are

Syncope, Angina, Dyspnea think S-A-D.

Oxygen extraction in coronary vessels, unlike other vascular beds, is near maximum at baseline. To increase oxygen delivery, coronary blood flow must be increased but this is limited by severe LV hypertrophy and increased left ventricular end diastolic pressure (LVEDP) causing endocardial compression (think compression of vasculature by massive left ventricular muscle) leading to impaired coronary perfusion pressure and myocardial ischemia with subsequent symptomatic AS.

Decreased exercise capacity and syncope are common presenting symptoms in AS. During normal exercise, systemic vascular resistance (SVR) decreases. The subsequent decrease in LV afterload allows for increased CO; however, in severe AS there is a fixed obstruction and the LV is unable to adequately generate increased CO causing patients to develop decreased exercise capacity and syncope.

Development of dyspnea secondary to heart failure in these patients is ominous and signals that compensatory LVH is no longer able to compensate for the worsening severe obstruction with resultant severe diastolic dysfunction and/or the development of systolic dysfunction with impaired EF (PMID: 33914604).

…and then there is the physical exam, which for those of us who have forgotten how to use a stethoscope, this may be just the time to brush the dust off it and take it to bedside!

Classical AS exam:

• High pitched mid-systolic ejection murmur at right upper sternal border (late peaking in severe AS)
• Paradoxically split S2 or inaudible S2 (severe AS)
• Pulsus parvus et tardus (weak delayed carotid pulse felt after S2 rather than simultaneously)
• S3 due to heart failure and/or S4 due to compensatory LVH

Diagnosis of Severe AS: 

Valvular heart disease is a great masquerader making diagnosis nuanced thus it is imperative to keep it at the forefront of every differential to prevent it from being missed. Diagnosis of AS is ultimately made via echocardiography; however, many routine tests that we obtain may give us additional clues such as an EKG with evidence of LVH and chest x-ray with evidence of aortic valve calcification.

As with our previous post on regurgitant valvular lesions CV-EMCrit 321, formal diagnosis of aortic stenosis is made via comprehensive echocardiography with guidelines for valvular assessment by ASE and EAE which include complex spectral and color wave doppler image acquisition to get precise measurements, perform complex calculations, and integrate multiple diagnostic criteria (PMID: 32314662)–exams that require extensive expertise and time.

Echocardiographic Definition of Severe AS:

PMID: 33914604

THINK 1440 for Classic Severe AS 

BUT TO OF COURSE COMPLICATE IT….

You can have low flow, low gradient AS where the valve area is <1cm2 but peak velocity and mean gradient DO NOT meet criteria for severe disease. This is seen in patients with reduced EF (classic low flow, low gradient) or preserved EF (paradoxical low flow/low gradient).

In classic low flow, low gradient with reduced EF, the weak ventricle is unable to generate enough flow (stroke volume) to create an elevated flow velocity or pressure gradient despite a severely stenotic valve.

Less intuitive, but in paradoxical low flow/low gradient AS, patients have a preserved EF but with SMALL CHAMBER SIZE and SMALL SV (stroke volume index <35 ml/m2 ) despite preserved EF.  This can be seen with patients with severe diastolic dysfunction or restrictive physiology with a hypertrophied ventricle. This small SV does not generate a high velocity flow or gradients despite small valve orifice.

But why should I care about low flow, low gradient AS?

Recognizing low flow, low gradient AS is imperative because it is not only common, with approximately 35-40% of patients with severe AS presenting with a low mean gradient (<40 mmHg) despite AV area <1 m2, but it is also associated with a worse prognosis. Low flow, low gradient AS is further characterized by a dobutamine stress test but that is a labor-intensive study not readily available for diagnosis in the rapidly decompensating patient! So how can I diagnose this emergently in my unstable patient (PMID: 33914604  & DOI: 10.5772/intechopen.84435)

… THE DIMENSIONLESS INDEX! But WAIT, before you SKIP to the next section to avoid the ultrasound deep dive I promise we will once again attempt to make valvular ultrasound simple!

The dimensionless index (DI) can be thought of as a ratio of the peak velocity of blood flowing through the left ventricular outflow tract (LVOT) divided by the peak velocity of blood flowing through the AV. In severe AS the narrow AV orifice will cause a significant increase in velocity as the blood flows through it compared to the wider LVOT.  Think of crimping a garden hose where suddenly decreasing the hose cross sectional area leads to faster flow or velocity. The velocity ratio obtained can be used to estimate the AV area as a proportion of the LVOT area. A ratio of less than 0.25 is concerning for severe AS. Commonly the velocity time integral (VTI) of the LVOT and AV obtained by spectral doppler is substituted for peak velocities to perform the DI (PMID: 33076698).

Qualitative point of care ultrasound (POCUS), using skills familiar to emergency medicine physicians.  One study showed that emergency medicine physicians, with limited echocardiogram training, were able to identify severe AS based off two echocardiographic views with good specificity (PMID: 25932319). The objective of this post is to focus on simple, efficient identification of acute SEVERE aortic stenosis causing decompensation, NOT a comprehensive review of aortic stenosis which is beyond the scope of this post.

POCUS Diagnosis

In 2D:

• Look for AV calcification, presence of LVH, AV leaflet mobility (very limited in severe AS)
• AV morphology (eccentric valve closure line on PSLA with m-mode suggesting bicuspid AV)
• Assess qualitative LV EF

Figure 4: Clip illustrating AV calcification with restricted AV leaflet mobility, courtesy of Randi Connor-Schuler MD

Next turn on spectral doppler. 

…WAIT DO WHAT? Thought you promised ultrasound made simple?

Now that we have discussed the basics…

In spectral doppler (apical 5 chamber view):

• Place pulse wave doppler (PWD) through LVOT and trace waveform to get LVOT VTI the same as you would when obtaining measurement to evaluate stroke volume

Figure 5: PWD through LVOT with waveform traced to obtain LV VTI, courtesy of Randi Connor-Schuler MD

• Place continuous wave doppler (CWD) through AV and trace waveform to automatically get aortic VTI, peak velocity (Vmax), peak gradient (maxPG), and calculation of mean gradient (mean PG) through the AV when using cardiac preset on ultrasound.
• Note it is important to use CWD through AV due to the higher velocities when compared to the lower LVOT velocities which are captured with PWD.
• Can SKIP the following for simplification if using cardiac preset, if NOT…

• • Peak velocity is obtained by measuring peak of AV VTI envelope, peak gradient can be calculated through modified Bernoulli equation as pressure gradient = 4Velocity²
  • Tracing AV VTI envelope will allow US to automatically calculate mean gradient
  • REMEMBER the machine is MEASURING VELOCITIES and using these to CALCULATE the gradients through the modified Bernoulli equation

Figure 6: CWD through aortic valve depicting elevated peak velocity, mean gradient and AVA of 1 cm consistent with severe AS, courtesy of Randi Connor-Schuler MD

• Obtain dimensionless index (DI) by dividing LV VTI by AV VTI as noted above

Remember AV mean gradient >40 mmHg, peak velocity >4 m/s, peak gradient >64 mmHg, and DI< 0.25 are consistent with severe AS. In low flow, low gradient AS may have a DI <0.25 indicating severe AS even though the velocities/gradients do not meet criteria for severe AS

Ultimately you can obtain the above discussed values with only TWO quick ultrasound measurements

• PWD through LVOT
• CWD through AV

Management:

ASK: Why did my patient with chronic AS develop heart failure and cardiogenic shock? Do they have progressive valvular or myocardial dysfunction with reduced EF or severe diastolic dysfunction, or did they decompensate secondary to a superimposed disease process? Important differentiation as treatment is different.

Focus of this post is management of severe AS presenting with hypotension and cardiogenic shock. Treatment of severe AS presenting with normotension or hypertension is nuanced and not the focus of this post as they do not typically present in extremis; however, it is worth noting that they can be preload dependent so it is best to avoid EXCESSIVE diuresis or venodilators as they can precipitate marked hypotension and instability. There may be times in the normotensive or hypertensive aortic stenosis patient, with reduced EF, that careful afterload reduction with vasodilators is beneficial but that is beyond the scope of this post. DOI: 10.1056/NEJMoa022021

Maintaining adequate diastolic blood pressure is vital to perfusing the hypertrophied LV in severe AS.

REMEMBER

Patients with severe AS who are hypotensive not only have low aortic diastolic pressure but also have an elevated LVEDP (secondary to the stenotic valve with pressure overload/LVH) causing significantly decreased CPP with subsequent myocardial ischemia, worsening myocardial dysfunction, and shock. Frequently these patients will require vasopressors to maintain adequate MAP/diastolic BP. Goal is to maintain adequate aortic diastolic pressure to ensure coronary perfusion but avoid excessive afterload.

When choosing a vasopressor avoid agents with significant chronotropic effects as they can impair diastolic filling time leading to decreased forward flow in an impaired ventricle with significant diastolic dysfunction and narrow valve orifice. Classic teaching is to use phenylephrine (pure alpha agonist) for treatment of severe AS with CS. This may be beneficial in pts with preserved EF (classic high flow, high gradient AS) to maintain MAP, CPP, and perhaps even cause reflexive bradycardia leading to increased diastolic filling time. Norepinephrine can be considered in patients with impaired forward flow as it has mild inotropic effects as well as vasopressor effects and is less likely to cause significant tachycardia such as epinephrine (PMID: 32314662).

In severe AS there is a fixed obstruction leading to increased afterload with subsequent marked LVH leading to diastolic dysfunction requiring higher filling pressures to maintain CO (ie preload dependent). Avoid venodilators and diuretics in these patients as they can cause acute decompensation. In patients presenting with severe AS and cardiogenic shock without evidence of volume overload (B-lines on POCUS, congestion on CXR) consider a 250 ml crystalloid bolus and reassess (PMID: 32314662).

Remember while these patients are dependent on higher filling pressures, elevated left sided pressures predispose them to functional MR, elevated PCWP, post-capillary pulmonary hypertension, and subsequent RV failure thus fluid administration must be judicious with constant reassessment of volume status.

Tachycardia can be maladaptive as it impairs diastolic filling time as well as decreases time for ejection through the severely stenotic aortic valve. Goal HR is slow to normal in the setting of AS with severe LVH and diastolic dysfunction.

Patients with classic low flow, low gradient AS with cardiogenic shock in the setting of reduced EF may require inotropic support. This is nuanced as inotropes can cause excessive chronotropy further impairing diastolic filling time thus inotropic agents must be utilized with care. Consider low dose inotropes that have less effect on chronotropy. Avoid beta blockers and calcium channel blockers that impair contractility.

Patients with chronic AS can have an acute decompensation in the setting of a systemic illness or stressor thus it is important to identify these stressors and treat any reversible causes.

• New onset atrial fibrillation with rapid ventricular rate can lead to decompensation due to loss of atrial kick as well as tachycardia which combined can significantly impair diastolic filling. Consider cardioversion in unstable patients.
• Sepsis presenting with low SVR state and hypotension can impair coronary perfusion pressure to severely hypertrophied ventricle with acute decompensation. Support MAP as noted above.
• Hypovolemia/ GI bleed can cause acute decompensation as these patients are preload dependent. Resuscitate as needed.

Intubation can cause hypotension (secondary to induction agents, decreased sympathetic response, PPV) thus impairing CPP leading to myocardial ischemia, worsening CS, and even cardiac arrest. If intubation is unavoidable resuscitate first.

• Have vasopressors such as phenylephrine or norepinephrine inline (or infusing)
• Consider a small fluid bolus,
• Use hemodynamically stable induction agents (consider awake intubation)
• Minimize peep as it can decrease preload

When severe AS is identified as the etiology of acute decompensated heart failure and cardiogenic shock (CS), definitive valve intervention is required. Many patients with CS secondary to severe AS may fail to stabilize with medical therapy alone and will require mechanical circulatory support (MCS) and/or temporizing balloon aortic valvuloplasty (BAV) as a bridge to definitive interventional or surgical treatment. Early consultation with interventional cardiology and/or cardiothoracic surgery is imperative.

MCS: Can consider IABP (decrease afterload, increase CPP & MAP), impella (can be difficult to place with severely stenotic AV), or V-A ECMO to help stabilize till definitive treatment.

Definitive treatment:

Surgical aortic valve replacement (SAVR), often considered the gold standard for severe AS treatment, is frequently associated with prohibitive surgical risk in patients with severe AS presenting in CS thus transcatheter aortic valve implementation (TAVI) is now the preferred definitive treatment in this population. Unfortunately, 30-day mortality in patients with severe AS causing CS undergoing emergent TAVI is as high as 33.3%, thus ideally patients should be stabilized hemodynamically with improving end organ function prior to undergoing TAVI. Balloon aortic valvuloplasty (primarily palliative due to early restenosis) can be used as a bridge to TAVI in patients unable to be stabilized by medical therapy plus MCS (PMID: 32314662).

Take Home Messages 

• Always include valvular heart disease in your differential in patients with unexplained shock
• Severe aortic stenosis is often associated with significant LVH & diastolic dysfunction making patients dependent on adequate preload and slower heart rates to allow time for LV filling
• Maintain adequate diastolic blood pressure to ensure coronary perfusion and prevent ischemia of the hypertrophied left ventricle
• Early consultation is imperative as these patients may need mechanical circulatory support or balloon aortic valvuloplasty in addition to medical therapy to stabilize them till definitive interventional or surgical treatment

Additional References/Resources:

• Western Sono: Dimensionless Index
• UBC IM POCUS: Aortic Stenosis vs Sclerosis
• Bicuspid Aortic Valve and Eccentricity Index
• Deranged Physiology: Aortic Stenosis

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Katrina Augustin

Cardiovascular Intensivist and emergency Medicine Consultant at Mayo Clinic, Rochester, MN Campus

Katrina (Trina) Augustin is a Cardiovascular Intensivist and Emergency Medicine consultant at Mayo Clinic in Rochester Minnesota where she also works as part of the ECMO team. She completed an Emergency Medicine Residency and chief residency at the University of Pittsburgh Medical Center. Trina's interests include cardiovascular critical care with a focus on mechanical circulatory support devices including ECMO. She is passionate about using FOAMed as an educational opportunity to improve the care of patients presenting with cardiovascular emergencies.

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