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1. What is the tilt test and how has it been adapted for use in patients with vasovagal syncope?
2. What are some of the weaknesses in the research utilizing the tilt test methodology?
3. What pharmacologic agents can increase the positive yield of the tilt test?
4. Are there any guidelines for tilt testing? More specifically what patients should not be tested in this manner?

1. 何为倾斜试验？该试验是如何用于血管迷走神经性晕厥患者的？
2. 倾斜试验方法学存在哪些缺陷？
3. 哪些药物可增加倾斜试验的阳性率？
4. 倾斜试验有没有指导方针？那些病人不能用该试验进行检测？

参考答案：

1.何为倾斜试验？该试验是如何用于血管迷走神经性晕厥患者的？

直立倾斜试验在特殊设计的倾斜床上进行，患者由仰卧位向直立位过渡，此时对于易感病人血管迷走性晕厥。该试验被认为通过导致静脉淤积并减少回心血量，因此触发Bezold-Jarisch机制，从而诱发血管迷走性晕厥。
对于有血管迷走性晕厥临床病史的病人，据报道倾斜试验的阳性率为30%-85%[2]。

2.倾斜试验方法学存在哪些缺陷？

由于所运用的实验方法非常繁多，这使得对倾斜试验的实验结果的解释和比较变得较为困难。因为倾斜前的仰卧时间和倾斜角度的非标准化，试验结果变化较大。最近很多研究采用仰卧30-45min和60-80度的倾斜角度[3]。此外，关于这种方法的特异性、灵敏度和复验性的问题使得所测数据解释很困难，同时临床应用受限。

3.哪些药物可增加倾斜试验的阳性率？

加用药物常可增加倾斜试验的阳性率。药物因其特殊作用而被选择使用，特别是作用于具有自律性的系统时。异丙肾上腺素、腺苷、硝酸甘油和滕喜隆是最常使用的药物。然而，这些结果尚不一致，并根据基础的症状、倾斜试验诊断记录和药物剂量的不同而变化。

4.倾斜试验有没有指导方针？那些病人不能用该试验进行检测？

美国心脏病学会出版了倾斜试验的指南[3]。倾斜试验不推荐用于曾经有过在低位现场所发生过1次晕厥而没有受伤的患者。此外，该试验禁用于有严重心脑阻塞性疾患者。总的来说，倾斜试验的根本用途尚未得到证实，然而，通过标准化诊断记录的进一步研究，将有希望证明该技术到底是应该推广还是弃用。

What is the tilt test and how has it been adapted for use in patients with vasovagal syncope?

The head-up tilt table testing is performed using a specially designed tilting table in which, when the patient is tilted from supine to upright positions, vasovagal syncope is precipitated in predisposed patients. The test has been thought to provoke vasovagal syncope by allowing venous pooling and decreased return to the heart, thus triggering the Bezold-Jarisch mechanism (1).
Patients with a clinical history of vasovagal syncope have been reported to have a positive tilt testing result in 30-85% of cases (2).

What are some of the weaknesses in the research utilizing the tilt test methodology?

Interpreting and comparing the results of tilt testing has been made difficult by the myriad of protocols that have been utilized. As the duration of recumbency prior to tilting and angle of the tilt are not standardized, they vary considerably. Most recent reports appear to use a recumbent duration of 30-45 minutes and tilt angles of 60-80 degrees (3). In addition, questions regarding the specificity, sensitivity, and reproducibility of this method have made it difficult to interpret the data and apply the results clinically.

What pharmacologic agents can increase the positive yield of the tilt test?

The addition of pharmacologic agents can often increase the positive yield of tilt table testing. Agents are selected for their specific effects, especially on the autonomic system. Isoproterenol, adenosine, nitroglycerin and edrophonium are common agents employed. The outcomes, however, have not been consistent, and vary according to the baseline symptomology, the tilt testing protocol, and the doses of the agents (2).

Are there any guidelines for tilt testing? More specifically what patients should not be tested in this manner?

The American College of Cardiology has published guidelines for head up tilt-table testing (3). Head up tilt table testing is not warranted in patients who have experienced a single syncopal episode without injury in an intermediate or low risk setting. In addition, this form of testing is contraindicated for patients with critical obstructive cardiac or cerebrovascular diseases. Overall the ultimate usefulness of the head up tilt table has not been definitively demonstrated, however, further work, with standardized protocols will hopefully demonstrate whether this technique should be embraced or abandoned.

Question Author: Lawrence Tsen, MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School

References:

1. Fitzpatrick AP, Zaidi A. Tilt methodology in reflex syncope: emerging evidence. J Am Coll Cardiol 2000 Jul;36(1):179-80.
2. Fenton AM, Hammill SC, Rea RF, Low PA, Shen WK. Vasovagal Syncope. Ann Intern Med. 2000;133(9):714-725.
3. Benditt DG, Ferguson DW, Grubb BP, et al. Tilt table testing for assessing syncope. American College of Cardiology. J Am Coll Cardiol. 1996 Jul;28(1):263-75.


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