Shalev Y, Gal R, Tchou P J, Anderson A J, Avitall B, Akhtar M, Jazayeri M R
Natalie and Norman Soref and Family Electrophysiology Laboratory, University of Wisconsin Medical School, Milwaukee.
J Am Coll Cardiol. 1991 Sep;18(3):746-51. doi: 10.1016/0735-1097(91)90798-e.
Two-dimensional echocardiography was performed during a head-up tilt test in 11 control subjects (group I) and 18 patients with recurrent unexplained syncope. In four patients (group II), the head-up tilt test was negative at baseline and after isoproterenol infusion. Syncope was induced during baseline head-up tilt in nine patients (group III) and after isoproterenol challenge in five (group IV). The echocardiographic variables assessed were left ventricular end-systolic and end-diastolic areas and percent fractional shortening. At the end of head-up tilt, end-systolic area decreased by 4.5 +/- 1.3 and 3.0 +/- 1.2 cm2 in groups III and IV, respectively, compared with 0.5 +/- 0.7 and 0.2 +/- 0.1 cm2 in groups I and II, respectively (p less than 0.04). Similarly, end-diastolic area decreased by 5.5 +/- 2.6 cm2 in group III compared with 2.7 +/- 1.9 and 1.75 +/- 0.4 cm2 in group I and II, respectively (p less than 0.04). Additionally, at the end of the baseline study, fractional shortening was significantly greater in group III and group IV (43 +/- 5%) than in groups I and II (p less than 0.01). In conclusion, syncope induced by head-up tilt is associated with vigorous myocardial contraction and a significant decrease in left ventricular end-systolic dimensions. This left ventricular hypercontractility may play an important role in the pathogenesis of syncope induced by head-up tilt.
对11名对照受试者（I组）和18名不明原因复发性晕厥患者进行了头高位倾斜试验期间的二维超声心动图检查。4名患者（II组）在基线和异丙肾上腺素输注后，头高位倾斜试验为阴性。9名患者（III组）在基线头高位倾斜期间诱发晕厥，5名患者（IV组）在异丙肾上腺素激发后诱发晕厥。评估的超声心动图变量包括左心室收缩末期和舒张末期面积以及缩短分数百分比。头高位倾斜结束时，III组和IV组的收缩末期面积分别减少4.5±1.3和3.0±1.2 cm²，而I组和II组分别减少0.5±0.7和0.2±0.1 cm²（p<0.04）。同样，III组舒张末期面积减少5.5±2.6 cm²，而I组和II组分别减少2.7±1.9和1.75±0.4 cm²（p<0.04）。此外，在基线研究结束时，III组和IV组的缩短分数（43±5%）显著高于I组和II组（p<0.01）。总之，头高位倾斜诱发的晕厥与心肌强烈收缩及左心室收缩末期内径显著减小有关。这种左心室高收缩性可能在头高位倾斜诱发的晕厥发病机制中起重要作用。
