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Explain the reason of tachycardia in hypertrophic cardiomyopathy

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"hypertrophic cardiomyopathy" AND tachycardia

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hypertrophic cardiomyopathy tachycardia mechanism diastolic filling authoritative

In hypertrophic cardiomyopathy (HCM), tachycardia is harmful mainly because it shortens diastole, the phase when the left ventricle fills and when coronary perfusion occurs.
The hypertrophied left ventricle is stiff and relaxes poorly, causing diastolic dysfunction and high filling pressures. It therefore needs adequate filling time. When heart rate rises:
  1. Less ventricular filling
    Diastole becomes shorter, so the stiff ventricle fills even less. Stroke volume and cardiac output may fall.
  2. Worsening LV outflow tract obstruction
    Lower filling means a smaller LV cavity. In obstructive HCM, this increases systolic anterior motion of the mitral valve and intensifies dynamic LV outflow tract obstruction. This can cause hypotension, presyncope, syncope, or dyspnea.
  3. Increased myocardial oxygen demand with reduced supply
    Tachycardia raises oxygen consumption. Meanwhile, shortened diastole reduces coronary blood-flow time. The thick myocardium may already have small-vessel dysfunction, so ischemia and chest pain can result.
  4. Loss of atrial contribution is particularly important
    Atrial contraction contributes substantially to filling of the noncompliant LV. Atrial fibrillation, often with a rapid ventricular rate, removes this atrial “kick” and can produce sudden hemodynamic deterioration.
  5. Arrhythmias may occur
    Fibrosis, myocardial disarray, ischemia, and adrenergic stimulation in HCM predispose to atrial and ventricular arrhythmias. Thus “tachycardia” can mean either compensatory sinus tachycardia or a clinically important tachyarrhythmia, including nonsustained ventricular tachycardia.
This is why beta-blockers and some non-dihydropyridine calcium-channel blockers are often used: slowing the heart rate improves diastolic filling and may reduce the obstruction gradient. Avoid assuming every fast pulse is benign in HCM, especially if accompanied by fainting, chest pain, breathlessness, or palpitations.
Textbook support: HCM has reduced LV compliance and raised filling pressure due to impaired diastolic function, and beta-blockade improves diastolic filling while attenuating adrenergic tachycardia. - Tintinalli's Emergency Medicine, relevant HCM pathophysiology section; Rosen's Emergency Medicine, HCM section. Recent evidence also continues to identify ventricular arrhythmias as an important prognostic issue in HCM, including this 2025 systematic review.

Explain double apical impulse, triple apical impulse and reverse split S2 in HCM

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hypertrophic cardiomyopathy double apical impulse triple apical impulse paradoxical reversed split second heart sound

In obstructive hypertrophic cardiomyopathy (HCM), the hypertrophied, stiff LV and dynamic LV outflow tract obstruction can create multiple palpable apical movements and delayed aortic valve closure.

1. Double apical impulse

A double apical impulse is two palpable outward movements at the apex:
  1. Presystolic impulse: caused by a forceful left-atrial contraction against a stiff, poorly compliant hypertrophied LV. It corresponds to a palpable S4.
  2. Systolic impulse: the normal ventricular systolic thrust, often forceful and sustained because the LV is hypertrophied.
So, in simple terms:
Atrial kick against stiff LV → palpable S4 → then LV systolic impulse
It is easiest to feel with the patient in the left lateral position. Harrison's describes a double apical impulse, with a palpable S2, in HCM. - Harrison’s Principles of Internal Medicine, 22e, physical findings section.

2. Triple apical impulse, or “triple ripple”

In obstructive HCM, three sequential apical movements may be felt:
  1. Presystolic wave: forceful atrial contraction into the noncompliant LV, corresponding to palpable S4.
  2. Early systolic wave: initial vigorous, relatively unimpeded LV ejection.
  3. Late systolic wave: continued forceful LV contraction against progressively worsening dynamic LV outflow tract obstruction.
The late systolic component occurs because systolic anterior motion of the mitral valve and septal contact progressively obstruct the LV outflow tract during systole. The ventricle is therefore contracting hard against an increasingly high intraventricular pressure gradient.
Sequence:
S4/presystolic atrial kick → early ejection → late systolic obstruction-related thrust
A forceful double or triple apical impulse is a recognized physical finding in obstructive HCM. - The Washington Manual of Medical Therapeutics, physical-examination section.

3. Reverse split S2, also called paradoxical split S2

Normally:
  • A2: aortic valve closure occurs first
  • P2: pulmonary valve closure occurs second
  • Inspiration delays P2 further, so the split becomes wider.
In obstructive HCM:
  • Severe dynamic LV outflow obstruction prolongs LV ejection time.
  • Therefore, aortic valve closure is delayed.
  • A2 occurs after P2.
Thus the order becomes:
P2 → A2
This is called reverse, paradoxical, or reversed splitting of S2.

Effect of inspiration

During inspiration, P2 is physiologically delayed. Because P2 moves closer to the already delayed A2, the split narrows or may disappear on inspiration. It is therefore best heard during expiration.

Mechanism in one line

Dynamic LV outflow obstruction → prolonged LV ejection → delayed A2 → P2 before A2.
Paradoxical S2 splitting is particularly associated with severe obstructive HCM and reflects marked prolongation of LV ejection due to the dynamic obstruction. - Fuster and Hurst’s The Heart, “Abnormal Splitting of S2” section.
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