Englund A, Fredrikson M, Rosenqvist M
Department of Cardiology, Karolinska Hospital, Stockholm, Sweden.
Circulation. 1997 Feb 18;95(4):951-4. doi: 10.1161/01.cir.95.4.951.
Patients with bifascicular block have an increased risk of syncopal attacks, but the underlying mechanism often remains unclear despite an extensive diagnostic workup. The head-up tilt test has been established as an important diagnostic tool in the unmasking of vasovagal syncope in patients with unexplained syncope. Its role in the evaluation of patients with bifascicular block has not been studied.
A head-up tilt test, using a 60 degrees angle of tilt for 45 minutes without pharmacological provocation, was performed in 25 patients with bifascicular block and syncope that remained unexplained after an extensive invasive and noninvasive electrophysiological investigation. As a control group, 25 subjects with bifascicular block without syncope, matched for age, sex, left ventricular function, and underlying heart disease, were included. A positive head-up tilt test was found in 7 (28%) of the syncope patients and in 8 (32%) of the control subjects (P = NS). Six patients, of whom 3 had a positive tilt test, had recurrent syncopal attacks during 32 months of follow-up. None of the control subjects had syncope during follow-up.
This study gives rise to serious concern regarding the specificity of the head-up tilt test in patients with bifascicular block. A head-up tilt test should therefore be interpreted with caution, and its role as a diagnostic tool in this patient category remains to be established.
双分支阻滞患者晕厥发作风险增加，但尽管进行了广泛的诊断检查，其潜在机制往往仍不清楚。头高位倾斜试验已被确立为不明原因晕厥患者中揭示血管迷走性晕厥的重要诊断工具。其在双分支阻滞患者评估中的作用尚未得到研究。
对25例双分支阻滞且晕厥患者进行了头高位倾斜试验，这些患者在广泛的有创和无创电生理检查后仍原因不明，试验采用60度倾斜角，持续45分钟，未使用药物激发。作为对照组，纳入了25例无晕厥的双分支阻滞患者，在年龄、性别、左心室功能和基础心脏病方面进行了匹配。晕厥患者中有7例（28%）头高位倾斜试验结果为阳性，对照组中有8例（32%）结果为阳性（P=无显著性差异）。6例患者（其中3例倾斜试验结果为阳性）在32个月的随访期间有反复晕厥发作。随访期间对照组无患者发生晕厥。
本研究引发了对双分支阻滞患者头高位倾斜试验特异性的严重关注。因此，对头高位倾斜试验的解读应谨慎，其作为该类患者诊断工具的作用仍有待确定。
