Faculty Bibliography

Systolic anterior motion of the mitral valve and mitral-septal contact is the usual cause of dynamic left ventricular outflow obstruction in hypertrophic cardiomyopathy. That true obstruction actually occurs is now established based on cardiac catheterization and echocardiographic evidence. A mid-systolic drop in left ventricular systolic ejection velocity because of obstruction has been demonstrated recently. Echocardiographic data indicate that systolic anterior motion of the mitral valve is initiated by flow drag; the mitral valve is swept toward the septum by the pushing force of flow. After mitral-septal contact, obstruction begets further obstruction as the pressure gradient pushes the mitral valve into the septum. Most symptomatic patients with obstruction can be treated successfully with negatively inotropic drugs. These medications reduce systolic anterior motion and obstruction by decreasing early left ventricular ejection acceleration, decreasing the early systolic pushing force on the protruding mitral leaflet. Patients who do not improve on medication generally benefit from surgery. Newer interventions to relieve obstruction, such as dual-chamber pacing and percutaneous transluminal septal myocardial ablation are under active investigation.

BACKGROUND: Drugs with negative inotropic effect are widely used to decrease obstruction in hypertrophic cardiomyopathy (HCM). However, the mechanism of therapeutic benefit has not been studied. METHODS AND RESULTS: We used M-mode, two-dimensional, and pulsed Doppler echocardiography to study 11 patients with obstructive HCM before and after medical elimination of left ventricular outflow tract obstruction. We measured 148 digitized pulsed Doppler tracings recorded in the left ventricular cavity 2.5 cm apical of the mitral valve. Successful treatment slowed average acceleration of left ventricular ejection by 34% (P=.001). Mean time to peak velocity in the left ventricle was prolonged 31% (P=.001). Mean time to an ejection velocity of 60 cm/s was prolonged 91% (P=.001). Before treatment, left ventricular ejection velocity peaked in the first half of systole; after successful treatment, it peaked in the second half (P=.001). In contrast, after treatment, we found no change in peak left ventricular ejection velocity. We also found no change in the distance between the mitral coaptation point and the septum, as measured in two planes, indicating no treatment-induced alteration of this anatomic relationship. CONCLUSIONS: Medical treatment eliminates mitral-septal contact and obstruction by decreasing left ventricular ejection acceleration. By slowing acceleration, treatment reduces the hydrodynamic force on the protruding mitral leaflet and delays mitral-septal contact. This, in turn, results in a lower final pressure gradient.

In many patients with obstructive hypertrophic cardiomyopathy, an abrupt mid-systolic drop in left ventricular ejection velocity can be detected. We analyzed 27 patients with obstructive hypertrophic cardiomyopathy who had 43 echocardiographic examinations (mean gradient 53 +/- 6 mm Hg). Exams showing a mid-systolic drop had higher mean outflow tract 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 left ventricular cavity and compared them with 90 continuous-wave tracings 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). There was also a close temporal correlation between the onset of the fall in pulsed velocity and the onset of M-mode mitral-septal contact (r = 0.95). CONCLUSIONS: The mid-systolic drop in left ventricular velocity is due to impedance to ejection and provides evidence of true obstruction. As left ventricular ejection velocity falls to its mid-systolic nadir because of impedance of ejection, velocity downstream in the left ventricular outflow tract actually rises to its peak. This disparity 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. The obstruction phase is best described as a time-dependent, amplifying feedback loop. The orifice narrows over time because of the rising pressure difference; the pressure difference rises over time because of the narrowing orifice.

Transesophageal echocardiography provided an accurate diagnosis of intimal flap prolapse into the left ventricle in all 6 of our patients. This complication of AD is a newly recognized and uncommonly discerned cause of severe AR

This report describes a spontaneous coronary artery dissection occurring during exercise in a long-distance runner who otherwise had a normal coronary arteriogram. This syndrome has been reported before and the two previous cases are reviewed. Coronary dissection is a rare cause of death during exercise

OBJECTIVES: The goal of this study was to investigate the hydrodynamic cause of mitral-septal contact and obstruction in patients with hypertrophic cardiomyopathy. BACKGROUND: Mitral-septal apposition has been shown to be the cause of obstruction in patients with hypertrophic cardiomyopathy. With obstruction, characteristic continuous wave Doppler tracings show an increasing acceleration of flow. (Tracing is concave to the left.) METHODS: We studied 24 consecutive patients who had a Doppler echocardiographic pressure gradient > or = 36 mm Hg. We pursued two lines of inquiry. 1) Before the onset of obstruction, we systematically measured the angle between the direction of left ventricular Doppler color flow and the protruding mitral leaflet in early systole. 2) After the onset of obstruction, we qualitatively analyzed the concave contour of the continuous wave Doppler tracings in our patients and developed a hydrodynamic theory of the obstruction phase to explain the characteristic tracings. We present a mathematic model to support this concept. RESULTS: We measured 129 angles. Just before mitral-septal contact, the protruding mitral leaflet projects at a mean 40 degrees and 45 degrees relative to flow in the apical long-axis and apical five-chamber views, respectively. At mitral-septal contact, the obstructing leaflet projects at a mean 52 degrees and 58 degrees relative to flow in the same respective views. Even very early in systole, at leaflet coaptation, 11 of 23 patients had angles > 15 degrees relative to flow. After mitral-septal apposition, obstruction across a cowl-shaped orifice begins. During this stage, the obstructing leaflet projects at a mean 55 degrees and 63 degrees relative to flow. In 22 patients, the continuous wave Doppler tracing of the left ventricular outflow jet showed an increasing acceleration of flow. CONCLUSIONS: Just before mitral-septal contact, the protruding leaflets project at high angles relative to flow. At these high angles, flow drag, the pushing force of flow, is the dominant hydrodynamic force on the protruding leaflet and appears to be the immediate cause of obstruction. The high angle between flow direction and the protruding leaflet precludes significant Venturi effects. Even earlier in systole, at leaflet coaptation, flow drag is dominant in half of the patients, with angles relative to flow > 15 degrees. After obstruction is triggered, it appears from our data and model that the leaflet is forced against the septum by the pressure difference across the orifice. The increasing acceleration of Doppler flow is explained by a time-dependent amplifying feedback loop in which the rising pressure difference across the orifice leads to a smaller orifice and a higher pressure difference.