肥大型閉塞性心筋症における左室流出路圧較差出現の機序—心房細動例における検討

A Doppler Echocardiograph Study on the Mechanism of Left Ventricular Outflow Obstruction in a Patient with Hypertrophic Cardiomyopathy and Atrial Fibrillation

　70歳，男性の肥大型閉塞性心筋症で，心房細動を伴った稀な1例において左室流出路圧較差出現の機序を心エコードプラー法を用いてニトログリセリン（NTG）舌下前後で検討した．1）先行R-R間隔と左室流出路圧較差はそれぞれ正相関を認め，NTG後に傾きが強くみられた．y＝60.2x−21.7,r＝0.70（Baseline），y＝193.2x−110.7,r＝0.81（AfterNTG），2） LVDdとstroke dimensionはNTG舌下前後でそれぞれ正相関を認めた．3）先行R-R間隔と左室拡張末期径（LVDd）はNTG舌下前後でほぼ同じ傾きを示した．4）先行R-R間隔の一致した心拍において左室流出路圧較差とfractional shorteningの関係は有意の正の相関を認め，NTG投与後に傾きが強く観察された．本症例では，NTG投与後の左室流出路圧較差の増大は，後負荷の減少と前負荷の減少を相殺するR-R間隔の延長によるFrank-Sterling機序による相対的左室流出路狭窄増強が推測された．

In a patient (70y.o.) with hypertrophic obstructive cardiomyopathy associated with atrial fibrillation, we studied the mechanism of left ventricular outflow obstruction using Doppler echocardiography. From the apical long axis view. the pressure gradient of left ventricular outflow obstruction was measured, and the left ventricular dimension was measured by M-mode echocardiography. The results were as follows : 1) There was a significant positive correlation between the preceding R-R interval and the pressure gradient before and after nitroglycerine (the slope of the relation gets steeper after nitroglycerine than before nitroglycerine). 2) There was a significant positive correlation between the preceding R-R interval and the left ventricular end -diastolic dimension before and after nitroglycerine. 3) There was a similar positive correlation between the left ventricular end-diastolic dimension and the stroke dimension before and after nitroglycerine (a steeper slope of the relation before nitroglycerine than after nitroglycerine). 4) There was a significant positive cor-relation between fractional shortening and the pressure gradient before and after nitroglycerine (a steeper slope of the relation after nitroglycerine administration than before). In conclusion, generally in a patient with hyper-trophic obstuctive cardiomyopathy, the mechanism of the left ventricular obstruction was thought to be depen-dent on the left ventricular end-systolic dimension, but in this case increase of the pressure gradient at the left ventricular outflow obstruction appeared, because of an increase of the left ventricular end-diastolic dimension to be mainly related to the Frank-Sterling mechanism. In addition, the interaction of the reduction of the afterload and the changes of the area of the left ventricular outflow obstruction appeared to be another mechanism which was involved.