By Vi Dinh, MD1,2, Stephanie Tseeng, MD1, Zan Jafry, MD1, Bradley Alice, MD1, Mark Schaefer, MD1 and Jeffrey Nakashioya, MD1
1Loma Linda University Medical Center, Department of Emergency Medicine
2Loma Linda University Medical Center, Department of Internal Medicine, Division of Pulmonary and Critical Care
Hypertrophic obstructive cardiomyopathy (HOCM) is an occasionally encountered and under-recognized clinical entity in the critical and emergency care environment. Point-of-Care Ultrasound (POCUS) can be utilized to better recognize HOCM and tailor resuscitation.
A 49-year-old man with a history of decompensated cirrhosis secondary to alcoholic liver disease, complicated by hepatic encephalopathy, hepatorenal syndrome, recurrent pleural effusions, and ascites was admitted to the medical intensive care unit (ICU) for septic shock. The patient eventually required mechanical ventilation, blood transfusions, IR embolization, multiple vasopressor support and broad-spectrum antibiotics. Physical exam was notable for a systolic murmur, prompting further investigation. POCUS findings were consistent with HOCM.
A frequently underappreciated cause of unexplained hypotension and shock, hypertrophic obstructive cardiomyopathy (HOCM) is of particular interest in the emergency department and critical care setting. The prevalence of HCOM in the general population is estimated at 1 out of 500 adults in one multi-ethnic study.1 HOCM, a genetic condition characterized by left ventricular hypertrophy, can result in a number of complications including left ventricular outflow tract (LVOT) obstruction, diastolic dysfunction, mitral regurgitation, and myocardial ischemia.2 LVOT obstruction is a particularly notable phenomenon as the resultant hypotension responds poorly to traditional treatments for cardiogenic hypotension. It may confound efforts to manage patients’ hemodynamic status. However, LVOT obstruction occurs in anatomically predisposed patients only under certain physiologic conditions, particularly changes in fluid status or end diastolic filling volume.3 Examples of LVOT precipitants include physical exertion, general anesthesia, cardiac surgery, or acute changes in cardiac function as in the case of MI or sepsis.3 Systolic anterior motion (SAM) of the anterior mitral valve is the most common cause of LVOT obstruction resulting from the impedance of blood flow by the displacement of the mitral valve against the septum during mid-systole.4 SAM and the septal hypertrophy of HOCM both can be easily identified on Point-of-Care Ultrasound (POCUS). Through an understanding the pathophysiologic and sonographic characteristics of HOCM and SAM, practitioners of POCUS can further enhance their care for hypotensive patients tailoring management accordingly.
Diagnosis, Ultrasound Findings, & Technique
Left ventricular septal thickness > 15 mm at any point along the septum is consistent with the diagnosis of hypertrophic obstructive cardiomyopathy, Table 1.
Table 1. HOCM Criteria
|BY THE NUMBERS|
|How to evaluate HOCM? |
Measure >= 15mm at any point on septum Fig. 1
Calculate Ratio –
· 1.3 Septum to Posterior Free Wall (non-hypertensive)
· 1.5 Septum to Posterior Free Wall (HTN)
How to evaluate for SAM?
M -mode cursor over anterior mitral valve leaflet (AMVL) – SAM Fig. 2
· Grade II <30% Septal contact time AMVL during systole
· Grade III >30% Septal contact time AMVL during systole
| Continuous Doppler – place over LVOT Fig. 3 |
· Evaluate for “dagger-like” morphology with very high velocities and peak gradient >30 mm Hg
Alternative diagnostic criteria involves the ratio of the septal measurement to the posterior free wall measurement. If the ratio is > 1.3 in non-hypertensive patients or > 1.5 in hypertensive patients the diagnosis of HOCM is made.5 These measurements are obtained by using the parasternal long axis and measuring the thickest portion of the interventricular septum, Figure 1.
FIGURE 1. Parasternal Long Axis demonstrates enlarged interventricular septum measuring 2 cm.
Once the diagnosis of HOCM is made, evidence of obstruction must next be established. SAM should be assessed by using m-mode on the parasternal long axis view, Figure 2.
FIGURE 2. In parasternal long axis view, M-mode cursor placed on the mitral valve demonstrates systolic anterior motion of anterior mitral valve leaflet.
SAM may result in left ventricular outflow tract (LVOT) obstruction when the anterior leaflet of the mitral valve comes in contact with the septum.5 While in the parasternal long axis view the m-mode cursor is placed over the anterior leaflet of the mitral valve to determine if the leaflet comes in contact with the septum during mid-systole. Normally, the anterior leaflet moves away from the septum during systole and then goes towards the septum during diastole. This is the same view to assess EPSS when estimating left ventricular ejection fraction. The presence of SAM indicates LVOT obstruction resulting in decreased cardiac output. The greater the duration of mitral valve leaflet to septum contact, the more significant the LVOT obstruction.5
Another technique to assess for LVOT obstruction in patients with HOCM is to assess the peak LVOT gradient. This is obtained using the apical 4-chamber view, Figure 3.
FIGURE 3. Continuous wave Doppler placed at the LVOT demonstrating “dagger like” morphology with high velocity (> 3m/s) and peak gradient >30 mm Hg.
The continuous wave Doppler gate is placed over the LVOT to determine the peak LVOT gradient and characteristic waveform pattern.7 Caution must be exercised to exclude the mitral jet, which is frequently present, and can be difficult to accurately assess particularly if the mitral jet is angled anteriorly.6 Once the continuous wave Doppler is obtained and the peak LVOT gradient is measured, obstruction is present if the gradient is > 30 mmHg and considered hemodynamically significant if >50 mmHg.8 About 25% of patients with HOCM will have resting LVOT pressures > 30 mmHg. An additional 50% more patients with HOCM will have LVOT peak gradients > 30 mmHg with exercise.6 A resting LVOT gradient > 30 mmHg is a predictor of HOCM related death.6
Pathophysiology and Management
In HOCM, left ventricular outflow tract obstruction is due to subaortic contact of the anterior leaflet of the mitral valve and the hypertrophied left ventricle during mid-systole. This results in resistance to forward flow through the outflow tract to the aorta leading to a reduced cardiac output and formation of a pressure gradient between the aorta and the left ventricle.9
The physiologic mechanisms in HOCM that contribute to SAM start with increased septal wall thickness which in turn narrows the LVOT. Apical papillary muscles may also act to pull the anterior leaflet of the mitral valve towards the ventricular septum. During systole a narrowed LVOT results in high velocity blood flow (principle of mass continuity) which results in a Venturi effect where a higher velocity fluid exerts a relatively lower pressure on its surroundings and pulls the anterior leaflet of the mitral valve into the LVOT. When SAM physiology occurs there can be a strong enough septal force on the anterior leaflet that a gap will form between the anterior and posterior leaflets of the mitral valve resulting in mitral regurgitation.1,3
The physiology of HOCM is further complicated by the dynamic nature of LVOT. Any mechanism that increases end diastolic volume (increased preload, increased filling time, increased afterload) results in widening of the LVOT and reduced obstruction. The opposite is true in that processes that lead to decreased end-diastolic volume (decreased preload, decreased filling time, or decreased afterload) result in worsened LVOT obstruction. Hence the murmur of HOCM which is contributed to by LVOT obstruction as well as mitral regurgitation is classically described as a systolic crescendo-decrescendo murmur that increases in intensity with upright posture from supine or squatting position or valsalva and is decreased in intensity with handgrip maneuvers, squatting, or leg raise. Understanding this physiology is key to improving cardiac output and therefore hemodynamics in patients with HOCM and comorbid critical illness.3,10
First line in management is to cease all agents that may increase inotropy, such as dobutamine or milrinone, as these can worsen SAM and consequent LVOT obstruction.8 The treatment of LVOT obstruction should be targeted at increasing afterload, increasing preload, decreasing the hart rate, and decreasing the LV contractility. Preload can be increased with crystalloid or colloid solutions. Increase in afterload may be accomplished by using an alpha-agonist such as phenylephrine. Nonvasodilating beta-blockers can be used cautiously to decrease the heart rate in order to increase the amount of diastolic volume.8
Given the finding of HOCM with SAM for our ICU patient, albumin boluses were administered and norepinephrine was replaced with phenylephrine (to increase afterload). The strategy reduced the obstructive process and improved systolic blood pressure significantly.
Take Home Points
POCUS can be relatively easily utilized in the emergency department and intensive care unit to evaluate critical patients for the presence of HOCM and SAM. The diagnosis of HOCM requires additional techniques building on the existing foundation of routine cardiac sonography that most emergency medicine and critical care physicians perform as a part of their practice. There is significant opportunity to further enhance the clinician’s POCUS skillset by evaluating for this disease process while significantly improving patient care.