Valvular Emergencies Part 2: Diagnosis and Management of Severe Aortic Regurgitation

December 25, 2020 via Shahriar Lahouti

CONTENTS

• Preface
• AV anatomy
  • Consideration
• Aortic regurgitation
• Differential diagnosis
• Bedside echocardiography in evaluation of severe AR in ED
• Management
  • Special conditions
• Going further
• Reference 

Abbreviations

2D, two-dimensional
ACC,American college of cardiology
ACS, acute coronary syndrome
AF, atrial fibrillation
ASE,American Society of Echocardiography
AV, aortic valve
AR, aortic regurgitation
AS, aortic stenosis
BAV, Bicuspid aortic valve
CM, cardiomyopathy
CWD, Continuous wave Doppler
CFD, color flow Doppler
EAE, European Association of Echocardiography
EF, ejection fraction
EROA, Effective regurgitant orifice area
LA, left atrium
LAE, left atrial enlargement
LAP, left atrial pressure
LV, left ventricle
LVE, left ventricle enlargement
LVOTO, left ventricular outflow tract obstruction
MV, mitral valve
MS, mitral stenosis
MR, mitral regurgitation
MVP, mitral valve prolapse
PAP, pulmonary arterial pressure
PLAX, parasternal long-axis
PSAX, parasternal short axis
PH, pulmonary hypertension
POCUS, point of care ultrasound
RA, right atrium
RV, right ventricle
TTE, transthoracic echocardiography
TEE, transesophageal echocardiography
TV, tricuspid valve
TR, tricuspid regurgitation
VHD, valvular heart disease
VC, Vena contracta
VCA, Vena contracta area
VCW, Vena contracta width.

 

Preface

In these series of valvular emergencies, identification of life threatening native valvular lesions in the emergency department are explored. Patients with aortic regurgitation can present with cardiorespiratory failure and a timely diagnosis and treatment is potentially crucial. Four essential questions should be considered when screening for valvular dysfunction by echocardiography in undifferentiated cardiorespiratory failure:

1. Is there a “severe” valvular dysfunction (in this case ‘severe AR)?
2. In the presence of the acute severe AR, what could be the possible etiology?
3. Does this explain my patient’s clinical presentation? 
4. How has this finding changed my management plan?

Aortic Valve anatomy

Aortic Root: Is a complex structure that connects the heart to the systemic circulation(figure 1). Distinct anatomical structures come together and make the aortic root1 (figure 2).

• AV leaflets: The three leaflets form the aortic valve. Each leaflet has 3 distinct anatomical parts shown below (figure 3).The echocardiographic representation of AV leaflets in PLAX is shown below (figure 4).
• Sinuses of valsalva: The three bulges of the aortic wall are named the sinuses of Valsalva (figure 3)
• Leaflet attachment: The leaflets attach to the aortic wall. At the site of their attachments they form a crown shaped thick fibrous structure called annulus (figure 5)

Sinotubular junction (STJ): The distal part of the sinuses toward the ascending aorta together with the commissures form a tubular structure called the “sinotubular junction” which separates the aortic root from the ascending aorta(Figure 1,5).

 

 

 

 

 

 

 

 

 

Considerations 

First: AV has three leaflets. This trileaflet design represents the optimal solution for low resistance valve opening and no other valve configuration can provide these characteristics, a fact prominently demonstrated in the setting of a bicuspid aortic valve (figure 6), in which some kind of valve dysfunction or degree of stenosis always co-exists depending on the configuration 2.

 

Second: AV leaflets are attached to the aortic root. In contrast to MV leaflets which are bounded by annulus, there’s no such a distinct histological entity or anatomical boundary in AV3. Moreover, The aortic valve is a mechanically passive valve. Absence of muscular structures with supporting strings (such as for MV), make AV less structurally dependent on the LV. This has hemodynamic implication:

👉While LV disease such as cardiomyopathy can cause LV enlargement and secondarily impacts MV function resulting to MR; such relation is not often true for AV. That is to say, AV function is not influenced by LV dysfunction. 

👉AV function is rather more influenced by upstream conditions such as HTN which can cause aortic root enlargement and results in AR.

Aortic Regurgitation

Definition: AR is caused by inadequate closure of AV leaflets which results in backflow of the blood into the LV during diastole

Clinical Presentation: The clinical presentation of AR depends on multiple factors including mechanism, etiology, and “severity” of AR, as well as course of the disease (rate of progression) and presence of other coexisting cardiac disease.

Severe acute AR commonly presents with signs of hemodynamic instability (dyspnea, syncope, or altered mental status) or frank cardiogenic shock. Other presenting symptoms are related to the cause of acute AR (eg, signs and symptoms of aortic dissection or endocarditis)

👉Patients with aortic dissection can present with a myriad of symptoms such as sudden onset of pain (chest/back/abdomen), syncope (due to development of tamponade), focal neurologic deficit (more on this here).

Patients with chronic AR may remain asymptomatic for decades, even if there is progressive ventricular dilation. Symptoms that develop in some patients with severe AR (stage D) include exertional dyspnea, angina, and other symptoms of heart failure

Mechanism and etiology of AR: Aortic regurgitation can be induced either by disease of the AV leaflets or by distortion or dilation of the aortic root and ascending aorta. The causes of acute and chronic AR with a native aortic valve 5 are listed in the following table (figure 7).

 

👉The two most common causes of acute AR of a native aortic valve are endocarditis and aortic dissection.

• Endocarditis leads to AR due to leaflet destruction or periaortic valvular abscess rupture.
• Aortic dissection can lead to AR through a variety of mechanisms, including extension of the dissection flap into the valve, involvement of a valve commissure that may result in inadequate leaflet support, dilation of the sinuses leading to incomplete coaptation of the leaflets, and/or prolapse of the dissection flap across the aortic valve, which impedes valve closure

👉Patients with BAV are at higher risk of aortic dissection. 

Severity and Course of the AR: As it has been eluded before, the main goal of screening for VHD in ED is to identify life threatening valvular emergencies or their associated conditions. Acute severe AR is usually a medical emergency since in contrast to chronic regurgitation which affords time for LV to dilate and accommodate the regurgitant flow, in acute regurgitation the lack of time for adaptation to additional blood volume leads to in an acute increase in LV diastolic pressure and a fall in forward cardiac output.

Hemodynamic impact of AR:

In Acute AR, the regurgitant volume fills the small LV that has not had time to dilate, resulting in an acute increase in LV diastolic pressure and a fall in forward cardiac output6.

• Increased LVEDP leads to an elevated LAP the development of pulmonary edema.
• Decreased forward flow leads to hypotension and cardiogenic shock 
  • Early closure of the MV (due to high LVEDP) and tachycardia (related to compensatory response to shock) both contribute to shortening of diastolic filling time and may exacerbate the  decline in forward flow.

In Chronic AR, the LV adapts over time to volume overload state induced by chronic AR (development of LV enlargement) and therefore is able to adapt to changes in pressure (LVEDP remains normal). This adaptive response will keep forward flow (cardiac output) within normal range 7 8.

👉Notably, acute exacerbation of chronic regurgitation may result in similar hemodynamic changes.

Presence of other cardiovascular disease:

Patients with small non-compliant LV due to pre-existing condition (e.g. systemic hypertension) are prone to acute changes in pressure and flow seen in acute AR and will develop more profound signs and symptoms following acute AR. 

 

Differential diagnosis 

Patients with acute moderate-severe AR or those with acute exacerbation of chronic AR present with acute pulmonary edema or cardiogenic shock. Importantly patients may present with signs and symptoms of underlying cause of AR (e.g. fever in endocarditis, and chest/back pain or syncope in aortic dissection).

Patients with acute AR due to aortic dissection can have extension into the right coronary artery and therefore may have ECG changes consistent with an acute inferior myocardial infarction.

Always consider aortic dissection in unstable patients with acute aortic regurgitation.

Bedside echocardiography in evaluation of severe AR in ED

Scope of the examination:

The qualitative and semi-quantitative method is an adapted time saving approach to diagnose severe native valve AR in ED and it incorporates 2D, CFD and PWD echocardiography which are explored below 9 10 11 12.

Examination technique

2D exam: Try to get a focused window of the interested valve (AV) in multiple views. 

First focus on aortic root size and presence of dissection flap in PLAX view. 

• Aortic root: Can be assessed qualitatively by eyeball. The rule of ⅓ implies that in PLAX view, ⅓ of the width of the screen on a vertical line is captured by RV outflow tract, aortic root and left atrium equally (figure 8). 
• Aortic root can be measured quantitatively at different levels (figure 9).
• Dissection (intimal) flap: Presence of intimal flap is a direct sign for aortic dissection though sometimes visualizing the flap is not easy. (more on this here)

Second: focus on AV leaflet morphology and motion which are usually best seen in the PLAX and PSAX view at the level of the aortic valve. Pay specific attention and look for:

• Leaflet morphology: Leaflet thickening, calcifications, vegetation (figure10), perforation, bicuspid valve?
• Leaflets Motion: Valve coaptation defect, flail leaflets?

👉Other echocardiographic data which can be discerned in 2D: LV and LA size, LV systolic function, function, and hypertrophy. Moreover indirect signs of aortic dissection in 2D echo are discernible as 13 :

• Dilatation of the aortic root
• Compression of the LA
• Pericardial and/or pleural effusion

 

 

 

 

Fig 10. Aortic valve endocarditis and vegetation

 

CFD exam: It can detect the presence of AR (figure 11) and also help to differentiate false lumen from true lumen in the presence of intimal flap in aortic dissection. AR in most patients is easily seen with CFD as a mosaic blend of colors originating from the AV during diastole. Although the apical approach is the most sensitive for detection of AR (even mild AR can be visualized), the PLAX is ok in the ED since the goal of screening for valvular disease in the ED is to identify ‘severe’ valvular dysfunction. 

It is important to visualize the three components of the color jet (flow convergence, VC, and jet area) for a better assessment of the origin and direction of the jet and its overall severity (figure 12).

Figure 11. CDF in PLAX view showing regurgitant flow through aortic valve 

 

 

 

Jet width in LV outflow tract (LVOT): The ‘LVOT’ is the region of the LV that lies between the anterior cups of the mitral valve and the ventricular septum (figure 13) 4.

From the PLAX view, the width of the AR jet can be measured (figure 14). This dimension is then divided to LVOT diameter to express the jet size as a percentage (relative size of the AR jet that occupies the LVOT). A ratio <25% generally indicates mild, 25%-64% indicates moderate, and ≧65% indicates severe AR 9. 

• Advantage of this method: Simple and rapid screen for detection of AR
• Limitation: May include:
  • Mostly applicable to central jets. It may overestimate AR in central jets as AR jet may expand unpredictably below the orifice
  • In an eccentric jet (figure 15), it underestimates the AR.

 

 

 

 

 

Vena contracta: The VC (is the narrowest area of the jet) is best visualized and measured in a zoomed, PLAX view. A VC of < 0.3 cm indicates mild, 0.3-0.6 cm indicates moderate, and > 0.6 cm indicates severe AR 9.

Flow convergence: It can be used for evaluation of AR severity similar to MR. Zooming on the LVOT in the PLAX views is the best approach to record the proximal flow convergence area 9.

PWD: Recording from the abdominal aorta normally should show no or just a brief early diastolic flow reversal. Holodiastolic flow reversal is an abnormal finding and when present in the abdominal aorta, it is a supportive finding for severe AR in the presence of other related findings 9 (figure 16). However, in the absence of AR, holodiastolic retrograde aortic flow can also be seen in other conditions (e.g  a left-to-right shunt across a patent ductus arteriosus).

 

Clinical question #2: I have performed POCUS on my critically ill patient and other diagnostic possibilities are less likely. AR is on top of my differential diagnosis list. Is this a severe AR? 

Since no single measurement or Doppler parameter is precise enough to quantify AR in individual patients, integration of multiple parameters is required as:

In the presence of ≧4 following strong parameters, AR is defined as severe and no further sophisticated and time consuming quantitative assessment is warranted 9.😀

• 2D echo: 
  • Flail valve, large coaptation defect. (Flail cups defined as complete eversion of a cusp into the LVOT in long-axis views)
  • LV dilatation, particularly with preserved LV function, is a supportive sign of significant AR and becomes more specific with exclusion of other causes of LV volume overload (e.g. ischemic dilated cardiomyopathy).
• CFD: presence of the following findings are specific for a severe AR:
  • Central jet width ≧65% of LVOT, or eccentric jet hugging wall of LVOT
  • Large flow convergence
  • Vena contracta width >0.6 cm
• PWD: Prominent holodiastolic flow reversal in the abdominal aorta (with end-diastolic velocity > 20cm/s)

In the presence of ≧4 following strong parameters, AR is defined as mild and no further sophisticated and time consuming quantitative assessment is warranted 9😀

• 2D: Normal aortic leaflets, normal LV size
• CFD: 
  • Jet size: small (<25%) in central jet
  • Flow convergence: None or very small
  • VCW: <0.3cm
• PWD: Absent or a brief early diastolic reversal in abdominal aorta

👉If 2-3 criteria for either mild or severe MR were met, then it’s “probably” moderate and further quantitative assessment is required which are beyond the scope of our discussion 9.

Bottom line: Since each echocardiographic parameter has its own advantages and limitations, try to evaluate and determine severity of AR by multiple methods. The following table (figure 17) summarizes the usefulness and limitations  of each method.

 

Management: General Strategy in ED

Clinical question #3: How has my management plan been changed by identifying a severe AR?

Patients with acute severe AR (and decompensated chronic MR) are critically ill with significant abnormalities that require emergent surgical treatment. Meanwhile temporary stabilization is attempted under close monitoring in the intensive care unit. The principles of stabilization of patients with acute severe AR is relatively similar to patients with acute severe MR (more on this here) and involve 14 15 16: 

• Improving oxygenation with BiPAP and in extreme cases possibly intubation
• Hemodynamic support in patients with low MAP and signs of poor organ perfusion with low dose epinephrine (e.g <8mcg/min), or possibly dobutamine
• Aggressive approach to terminate significant dysrhythmias 

While intra-aortic balloon pumps in patients with acute severe MR may be considered as a temporizing measure; in acute severe AR it is contraindicated as the inflation of the balloon worsens the regurgitant flow across the aortic valve during diastole and precipitates worsening of forward flow 17 .

Special conditions

Aortic Dissection: The only effective treatment for patients with aortic dissection and concomitant acute severe AR is emergency surgery. Interim medical treatment is guided by clinical presentation and especially systolic blood pressure. If the patient is hypertensive vasodilator therapy with cautious use of beta blockers may be considered. Although standard recommendations for beta-blocker therapy patients with aortic dissection suggest a target heart rate <60 BPM prior to initiation of vasodilator therapy, in patients with concomitant acute severe AR, such heart rate lowering may not be tolerated; and a higher target may be more appropriate.

👉Patients with aortic dissection and severe AR are not well tolerable to beta-blockers since it blocks the compensatory tachycardia and may cause profound hypotension 18. 

Endocarditis: Start broad spectrum antibiotic (class I recommendation) 19 and involve cardiothoracic surgery.

 

Going Further

• Ultrasound of cardiac valves (part 1)
• Ultrasound of cardiac valves (part 2)
• Cardiogenic Shock (EM:RAP)
• Resuscitation of CHF with Cardiogenic Shock (EM:RAP)

 

Post Peer Reviewed by: Reza Moazzeni, M.D. and Mojtaba Chardoli, M.D.

 

References

Expand to view the reference list

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