Septal artery diastolic flow profile in hypertrophic restrictive cardiomyopathy: Doppler square root sign!

Septal artery flow in normal individuals occurs almost exclusively during diastole with little to no flow during systole. The flow is similar in hypertrophic cardiomyopathy (HCM), predominantly diastolic flow with blunted systolic flow or systolic flow reversal. However, the diastolic flow velocities are higher than in normal subjects (Panel A). We present a 19-year-old patient with HCM, marked septal hypertrophy (41 mm), and reduced regional strain (Panels B–D). No left ventricular outflow tract obstruction was noted even with provocation. Mitral inflow and tissue Doppler assessment confirmed Grade 3 diastolic dysfunction (restrictive pattern): E wave velocity 0.92 m/s, A wave velocity 0.33 m/s (E/A ratio 2.8), deceleration time 128 ms, and septal E' velocity 5.1 cm/s (Panels E and F). The septal arteries were identified using colour-flow imaging (Panel G). Pulsed-wave Doppler of the septal artery demonstrated a unique flow pattern, shown in Panel H. During early systole, marked flow reversal was noted, velocity 1.6 m/s (arrow) followed by no flow during the remainder of systole (asterisk). This is attributed to systolic compression 'milking' of the septal artery by the hypertrophic septum. During diastole, initial high velocity (1.2 m/s) rapid forward flow 'dip' was noted followed by an abrupt reduction and plateauing of velocity to 0.3 m/s, dip and plateau pattern reminiscent of a square root sign. We suggest that this septal flow profile is as a result of restrictive filling of the left ventricle, square root sign, resulting in rapid near-equalization of diastolic pressures in the septal artery and left ventricle, thus reducing the perfusion pressure.

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