Biphasic left ventricular outflow and its mechanism in hypertrophic obstructive cardiomyopathy.
BACKGROUND
Biphasic systolic velocity in the left ventricular (LV) outflow tract (LVOT) occurs in hypertrophic obstructive cardiomyopathy (HOCM). The cause and importance of this observation remain poorly understood.


METHODS
A total of 25 patients with HOCM were matched to 30 control subjects. A function derived from the relation of flow in the proximal descending aorta to that in the LVOT was used to estimate the LVOT systolic flow rate in HOCM. Patients with HOCM were grouped by absence (group I) or presence (group II) of biphasic LVOT velocity.


RESULTS
Biphasic LVOT velocity was associated with biphasic estimated LVOT outflow (P =.002). The LVOT pressure gradient was inversely related to LV outflow rate at the time of the peak gradient (r = -.64, P <.001). Dobutamine increased the gradient and reduced LVOT outflow at the time of the peak gradient. In group II, mitral-septal separation occurred despite a LVOT gradient (36 mm Hg).


CONCLUSIONS
Biphasic LVOT flow in HOCM occurs and may be caused by "afterload mismatch." The late systolic increase in flow is related to mitral-septal separation. Resolution of systolic anterior motion occurs despite a persistent LVOT pressure gradient, implying a role for forces other than pressure differences.
Conklin
Heidi M
HM
Division of Cardiology, Oregon Health and Science University, Portland 97239, USA.
Huang
Xiaoyan
X
Davies
Crispin H
CH
Sahn
David J
DJ
Shively
Bruce K
BK
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D002312:Cardiomyopathy, Hypertrophic / Q000000981:diagnostic imaging / Q000503:physiopathology*; D004280:Dobutamine / Q000008:administration & dosage; D004452:Echocardiography; D017548:Echocardiography, Transesophageal; D005260:Female; D006346:Heart Septum / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D008944:Mitral Valve Insufficiency / Q000000981:diagnostic imaging / Q000503:physiopathology; D013223:Statistics as Topic; D013318:Stroke Volume / Q000502:physiology; D013599:Systole / Q000502:physiology; D014694:Ventricular Outflow Obstruction / Q000000981:diagnostic imaging / Q000503:physiopathology*
D000318:Adrenergic beta-Agonists; D004280:Dobutamine