Why there is sudden dip in ejection velocity /pressure or fast fall in pulse (in pulsus biseriens) in HOCM?

In Hypertrophic Obstructive Cardiomyopathy (HOCM), pulsus bisferiens is a characteristic arterial pulse pattern characterized by a double-peaked pulse wave. The sudden dip or trough in the pulse wave is a prominent feature of this phenomenon and can be attributed to the unique pathophysiological changes that occur in HOCM.

Here’s why this sudden dip or trough occurs in the pulse wave associated with pulsus bisferiens in HOCM:

  1. Dynamic Left Ventricular Outflow Tract (LVOT) Obstruction:
  • HOCM is characterized by abnormal thickening of the septum and left ventricular muscle, particularly the subaortic region. During systole, as the left ventricle contracts and attempts to eject blood into the aorta, the hypertrophied septum can obstruct the LVOT, creating resistance to blood flow.
  1. Initial Ejection: At the onset of systole, the left ventricle contracts, and blood is forcefully ejected into the aorta. This results in the first, sharp peak of the pulse wave.
  2. Mid-Systolic Dip (Trough):
  • Following the initial peak, the blood encounters resistance due to the hypertrophied septum and dynamic LVOT obstruction. This resistance causes a momentary decrease in the velocity and pressure of blood flow, resulting in a mid-systolic dip or trough in the pulse wave.
  1. Relief of Obstruction and Second Ejection Peak:
  • Subsequently, as more blood is ejected and the septum moves slightly away from the LVOT, the obstruction is relieved temporarily. This relief allows for a second, smaller ejection peak in the pulse wave.

The mid-systolic dip (trough) in the pulse wave is a characteristic feature of HOCM and is directly related to the dynamic obstruction of the LVOT during systole. The relief of this obstruction during the cardiac cycle results in the characteristic double-peaked or bisferiens pulse pattern seen in HOCM. Understanding this hemodynamic pattern is crucial for the diagnosis and management of HOCM.