MIDSYSTOLIC DROP IN LEFT-VENTRICULAR EJECTION VELOCITY IN OBSTRUCTIVEHYPERTROPHIC CARDIOMYOPATHY - THE LOBSTER CLAW ABNORMALITY

In many patients with obstructive hypertrophic cardiomyopathy, an abru pt mid-systolic drop in left ventricular ejection velocity can be dete cted. We analyzed 27 patients with obstructive hypertrophic cardiomyop athy who had 43 echocardiographic examinations (mean gradient 53 +/- 6 mm Hg). Exams showing a midsystolic drop had higher mean outflow trac t pressure gradients (90 +/- 6 compared with 29 +/- 4 mm Hg, p < 0.001 ). After medical elimination of obstruction, the mid-systolic drop was no longer seen. We measured 105 pulsed-wave Doppler tracings in the l eft ventricular cavity and compared them with 90 continuous-wave traci ngs through the outflow tract. There was. a close temporal correlation between the nadir of the left ventricular velocity drop and the peak continuous-wave left ventricular outflow tract velocity (r = 0.99). Th ere was also a close temporal correlation between the onset of the fal l in pulsed velocity and the onset of M-mode mitral-septal contact (r = 0.95). Conclusions: The mid-systolic drop in left ventricular veloci ty is due to impedance to ejection and provides evidence of true obstr uction. As left ventricular ejection velocity falls to its mid-systoli c nadir because of impedance of ejection, velocity downstream in the l eft ventricular outflow tract actually rises to its peak. This dispari ty in the two velocities, deceleration in the left ventricular cavity and acceleration in the left ventricular outflow tract, indicates that the outflow orifice is progressively narrowed over time as the mitral valve is forced into the septum by the rising pressure difference. Th e obstruction phase is best described as a time-dependent, amplifying feedback loop. The orifice narrows over time because of the rising pre ssure difference; the pressure difference rises over time because of t he narrowing orifice.