The major mechanism of exertional dyspnea in HOCM is due to
- Hypercontractile LV
- LVOT obstruction
- Diastolic dysfunction
- Mitral regurgitation
- Unrelated to HOCM
Answer : 3*
*This has been proven by a simple fact , dyspnea continues to be a prime symptom in both obstructive as well as non obstructive HCM
Though LVOT obstruction appears to be the core issue , the myocardial disarray is a global one and lies scattered .That is why , myomectomy , septal reduction , may not reduce the symptoms grossly as one would expect.
Paradoxically , preload reduction with diuretics (That works well for most dyspnea with raised LVEDP) , is vested with the risk of worsening the symptoms in HOCM . Diuretics underfill the LV and tend to aggravate dynamic LVOT obstruction.
Probably ,the best way to reduce symptom of dyspnea is to keep the heart rate low with betablocker.Further, betablockers smoothen the LV wall stress and calm down the LV baroreceptors which indirectly suppress the afferent input in the brainstem dyspnea circuit.