Dynamic left ventricular outflow tract obstruction (LVOTO) is not a condition I learned about during residency, and it is not a condition I have diagnosed regularly, although I have probably missed it many many times. On First10EM, I usually prefer to start with a presenting symptom than a diagnosis, because that is how patients present. […]
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The phenomenon of dynamic left ventricular outflow tract obstruction, or DLVOTO, describes an obstruction to blood flow out of the left ventricle during systole. While most commonly associated with hypertrophic obstructive cardiomyopathy, it can also develop in other conditions such as stress induced Takotsubo cardiomyopathy, septic shock, hypovolemia from various causes, and other hyperdynamic states.
The primary mechanism involves the systolic anterior motion of the mitral valve leaflet, typically the anterior leaflet, which moves towards and obstructs the septal wall. This movement is often driven by a combination of factors including a small, hyperdynamic left ventricle, increased myocardial contractility, reduced preload, and reduced afterload. The Venturi effect, where high velocity blood flow through a narrowed outflow tract pulls the mitral leaflet towards the septum, plays a significant role. Displacement of the papillary muscles can also contribute to directing the mitral leaflet into the outflow tract.
Clinically, DLVOTO can lead to reduced cardiac output, hypotension, and shock. It increases myocardial oxygen demand and can cause myocardial ischemia or pulmonary edema. Mitral regurgitation is a frequent accompanying finding due to the abnormal mitral valve leaflet motion.
Diagnosis typically relies on echocardiography. Key findings include visible systolic anterior motion of the mitral valve leaflet, often with an associated posterior jet of mitral regurgitation, a small and hyperdynamic left ventricle, and a measurable pressure gradient across the left ventricular outflow tract. A gradient greater than two or three meters per second suggests significant obstruction.
Treatment strategies focus on reversing the underlying physiological imbalances. Increasing left ventricular preload with intravenous fluids is a crucial first step, particularly in cases of secondary DLVOTO caused by hypovolemia or sepsis. Reducing myocardial contractility is also vital, for which beta blockers are the preferred agents. They slow the heart rate, allowing for increased ventricular filling time, and decrease the force of myocardial contraction. Increasing afterload using pure alpha adrenergic agonists like phenylephrine can also be beneficial by increasing systemic vascular resistance, which helps to push the septum away from the mitral valve leaflet.
It is critical to avoid certain medications that can worsen DLVOTO. These include vasodilators, such as nitroglycerin or nitroprusside, which reduce afterload, and positive inotropes, such as dobutamine or high dose epinephrine, which increase myocardial contractility. In septic patients with DLVOTO, phenylephrine or vasopressin may be considered over norepinephrine if inotropic effects are deemed detrimental.
https://first10em.com/dynamic-left-ventricular-outflow-tract-obstruction/
