Intracavitary Gradient

November 19th, 2012

A systolic gradient across the LVOT is a typical feature of hypertrophic obstructive cardiomyopathy (HOCM). This so-called dynamic outflow obstruction can lead to reduced stroke volume and thereby systolic hypotension. Maneuvers that increase inotropy or reduce LV cavity size will worsen the gradient and may set off a downward spiral (eg strain phase of the Valsalva maneuver). Occasionally, one can detect a gradient within the LV even though other features of HOCM are absent. Typically the CW envelope appears dagger-shaped and may be imbedded in the CW signal of mitral MR. This type of gradient is usually mid-cavitary meaning between the apex and the base of the LV. Due to small LV cavity size and variable degrees of concentric LVH the mid-cavitary segments may thicken more causing the LV to take the shape of an hour-glass in late systole. This usually occurs in late systole when the majority of blood volume has already been ejected from the LV into the aorta. The small volume of blood caught in the LV apex at this time is not significant and therefore mid-cavitary gradients do not cause low cardiac output states as LVOT gradients can do. The degree of the mid-cavitary gradient is independent from the amount of blood caught in the LV apex. Even very small amounts can cause high gradients.
To confirm the approximate location of the gradient the echocardiographer can use PW-Doppler and slowly move the sample volume from the apex to the base of the LV. The position of the sample box with a sudden increase in flow velocity signifies the location of the mid-cavitary obstruction.