倾斜试验在晕厥诊断中的作用

倾斜试验是晕厥诊断中非常重要的辅助检查之一,该检查于1986首次提出,通过变换体位模拟神经介导性反射寻找晕厥病因并指导治疗。该检查主要用于反射性晕厥、直立性低血压所致晕厥的诊断,同时对于晕厥与其他心源性晕厥、癫痫、心因性假性晕厥等疾病的鉴别诊断也有一定作用,但其敏感性和特异性有限。倾斜试验阳性的反射性晕厥患者,接受起搏治疗前要综合评估患者情况。     

Single-stage adenosine tilt testing in patients with unexplained syncope

INTRODUCTION: We previously have shown that a 3-minute single-stage adenosine tilt test has a diagnostic yield comparable to a two-stage protocol consisting of a 30-minute drug-free tilt followed by a 15-minute isoproterenol tilt. In this study, we sought to further define the clinical utility of adenosine tilt testing in patients with unexplained syncope by prospectively evaluating test specificity and determining predictors of a positive test response. METHODS AND RESULTS: The specificity of single-stage adenosine tilt testing was determined using 30 control subjects. To determine the diagnostic yield of this protocol, adenosine tilts were performed in 129 patients with unexplained syncope. The adenosine tilt test protocol had high specificity (100%) but a low overall diagnostic yield (18%). However, the yield was affected significantly by age. In patients /=65 years of age (2/41 patients [5%], P < 0.0001). CONCLUSION: These data support single-stage adenosine tilt testing in patients 40 years of age is low, suggesting that the clinical utility of this protocol is limited in these patients.     

Methodology of head-up tilt testing in patients with unexplained syncope

Prolonged 60 degree head-up tilt has been shown to be valuable in the investigation of unexplained syncope, diagnosing neurally mediated bradycardia/hypotension or malignant vasovagal syndrome. To evaluate the methodology of tilt testing, the following were examined: reproducibility of results, tilt duration, angle of tilt, method of tilt support and effect of age in patients and control subjects. Seventy-one patients with recurrent unexplained syncope underwent 60 min of 60 degree tilt; 53 (75%) had an abnormal test with vasovagal syncope at 24 +/- 10 min (mean +/- SD). Tilting to 60 degrees resulted in an abnormal test in only 2 (7%) of 27 control subjects without cardiovascular symptoms (p less than 0.001); and 5 (15%) of 34 patients with syncope and documented conduction tissue disease (p less than 0.001). Of 15 youthful fainters, 3 (20%) had vasovagal reactions as did 1 (8%) of 12 asymptomatic youthful control subjects. These 12 control subjects also underwent tilting with a saddle support and 7 (67%) had vasovagal reactions. It is concluded that the duration of tilting at 60 degrees should be 45 min (mean time to syncope +2 x SD in the 53 patients with abnormal results). Twenty percent of patients with an abnormal tilt test may not demonstrate syncope with repeat tilting. Saddle tilt testing in unexplained syncope may result in a loss of specificity. Tilting at less than 60 degrees results in a loss of sensitivity. Head-up tilt may be less useful in youthful subjects with vasovagal syncope than in other subjects.     

硝酸甘油激发的倾斜试验在血管迷走性晕厥中的应用

目的了解在倾斜试验中,用硝酸甘油进行激发对于血管迷走性晕厥(vasovagalsyncope,VVS)患者的诊断价值,通过观察VVS患者晕厥前后的血流动力学改变及心率变异性功率谱变化,探讨VVS的发病机制。方法55例不明原因,反复发作的晕厥患者及20例健康人行直立倾斜试验,倾斜75°持续45min,阴性者舌下含服0.3mg硝酸甘油后倾斜至75°持续20min,观察有无阳性反应。倾斜过程中动态监测心电图、血压和心率,并进行心率变异性分析。结果病例组55例中32例出现阳性反应,8例于基础倾斜试验阶段出现阳性反应,24例于硝酸甘油激发后出现阳性反应,阳性率从14.55%升高到58.18%。阳性反应中,血管抑制型(VD)21例,占65.63%,心脏抑制型(CI)5例,占15.63%,混合型(MX)6例,占18.75%。对照组20例中4例出现阳性反应。CI型患者倾斜后心率上升,达高峰后在短期内急剧下降,发生晕厥,血压也略下降;MX型患者晕厥时心率及血压均在短期内急剧下降;VD型患者晕厥时血压在短期内急剧下降,心率也发生一定程度的下降,下降百分比小于CI型及MX型(P<0.05)。倾斜后阳性组LFnorm增高,HFnorm下降,LF/HF增高,晕厥前LFnorm及LF/HF达到最大值,HFnorm达到最低值,晕厥时LFnorm及LF/HF显著下降,HFnorm增加。结论硝酸甘油激发能增加倾斜试验的阳性率,自主神经功能改变(交感活性迅速减退,迷走神经兴奋)为晕厥产生的主要机制,并在不同患者产生不同的血流动力学改变。     

Methodology of isoproterenol-tilt table testing in patients with syncope.

To assess the impact of isoproterenol, duration of tilt, symptom development and hemodynamic changes on the outcome of tilt table tests, 100 patients with syncope underwent successive 80 degrees head-up tilt for 10 min during infusions of 0, 2 and 5 micrograms/min of isoproterenol. All 15 patients with another cause of syncope had a normal test result and 66 (78%) of the 85 patients with syncope of unknown origin had a test that resulted in syncope or presyncope. Isoproterenol was required to produce syncope or presyncope in greater than 90% of positive tests and 66% to 80% of positive tests required a dose of 5 micrograms/min of isoproterenol. Without isoproterenol, symptoms did not develop until after greater than or equal to 4 min of head-up tilt. With either 2 or 5 micrograms/min of isoproterenol, the half-time of symptom onset was 0.7 to 1.9 min and the rate of symptom development did not depend on the dose of isoproterenol. During syncope, the mean heart rate, systolic blood pressure and rate-pressure product each decreased significantly from 132 +/- 21 to 67 +/- 25 beats/min, 117 +/- 19 to 60 +/- 16 mm Hg and 15.3 +/- 2.9 to 4.2 +/- 2.2 x 10(3) mm Hg/min, respectively. During presyncope, mean trough rate-pressure product (5.5 +/- 2 x 10(3) mm Hg/min) was significantly higher (p = 0.027) than during syncope.(ABSTRACT TRUNCATED AT 250 WORDS)     

硝酸甘油激发的倾斜试验在血管迷走性晕厥中的应用

目的:了解在倾斜试验中,用硝酸甘油进行激发对于血管迷走性晕厥(VVS)患者的诊断价值,并通过观察VVS患者晕厥前后的血流动力学改变及心率变异性功率谱变化,以探讨VVS的发病机制。方法:55例不明原因反复发作晕厥患者(病例组)及20例健康者(对照组)行直立倾斜试验,倾斜75°持续45min,阴性者舌下含服0.3mg硝酸甘油后倾斜至75°持续20min,观察有无阳性反应。倾斜过程中动态监测心电图、血压和心率,并进行心率变异性分析。结果:病例组55例中32例出现阳性反应(阳性率为58.2%),8例于基础倾斜试验阶段出现阳性反应,24例于硝酸甘油激发后出现阳性反应;32例中,血管抑制型(VD型)21例,心脏抑制型(CI)5例,混合型(MX)6例。对照组20例中4例出现阳性反应。病例组中CI型患者倾斜后心率上升,达高峰后在短期内急剧下降,发生晕厥,血压也略下降;MX型患者晕厥时心率及血压均在短期内急剧下降;VD型患者晕厥时血压在短期内急剧下降,心率也发生一定程度的下降,下降百分比小于CI型及MX型(P<0.05)。倾斜后阳性者低频标化植(LFnorm)增高,高频标化值(HFnorm)下降,低高频比值(LF/HF)增高,晕厥前LFnorm及LF/HF达到最大值,HFnorm达到最低值,晕厥时LFnorm及LF/HF显著下降,HFnorm增加。结论:硝酸甘油激发能增加倾斜试验的阳性率,自主神经功能改变(交感活性迅速减退,迷走神经兴奋)为晕厥产生的主要机制,并在不同患者产生不同的血流动力学改变。     

Electrophysiologic testing in patients with unexplained syncope: clinical and noninvasive predictors of outcome

To assess whether the level of risk of having significant electrophysiologic abnormalities can be determined, 29 clinical variables were analyzed in 104 patients with unexplained syncope who underwent electrophysiologic testing. A positive electrophysiologic study was defined as: a sinus node recovery time greater than or equal to 3 seconds; HV interval greater than or equal to 100 ms; infranodal block during atrial pacing; unimorphic ventricular tachycardia; and supraventricular tachycardia associated with hypotension. Thirty-one patients had a positive study, with inducible ventricular tachycardia being the most common finding (71% of positive studies). A left ventricular ejection fraction less than or equal to 0.40 was the most powerful predictor of a positive electrophysiologic study (p less than 0.00001), followed by the presence of bundle branch block (p less than 0.00003), coronary artery disease (p less than 0.0003), remote myocardial infarction (p less than 0.00006), use of type 1 antiarrhythmic drugs (p less than 0.00003), injury related to loss of consciousness (p less than 0.01) and male sex (p less than 0.01). A negative electrophysiologic study was associated with an ejection fraction greater than 0.40 (p less than 0.00001), the absence of structural heart disease (p less than 0.00001), a normal electrocardiogram (ECG) (p less than 0.0001) and normal ambulatory ECG monitoring (p less than 0.0001). The probability of a negative study increased as the number and duration of syncopal episodes increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Repeated tilt testing in patients with tilt-positive neurally mediated syncope.

In this study we have included 222 patients with apparent neurally mediated syncope and with a positive diagnostic tilt test. The mean age was 33.4+/-21.2 years (median 25.3): there were 107 men (median age 25.3) and 115 women (median age 22.6). The age difference between males and females was statistically significant (P = 0.002). The response to the diagnostic tilt test was: type 1 (mixed) in 74 patients; type 2A (cardioinhibitory and bradycardia) in 6; type 2B (cardioinhibitory and asystole) in 61; type 3 (vasodepressor) in 81. In all 222 patients the diagnostic tilt test was positive after 19+/-11 min (mean+/-SD), median time: 18 min. For the four types of syncope, the duration in minutes of the diagnostic tilt test was: type 1 (mixed) 19.5+/-11.4; type 2A (cardioinhibitory) 24.8+/-13.6; type 2B (cardioinhibitory and asystole) 14.7+/-10.2; type 3 (vasodepressor) 21.6+/-11.1. A significant difference was found between type 2B and type 3 responses (P = 0.002). Between males and females no significant differences in the duration of the diagnostic tilt test were found, neither for all responses, nor for the four subtypes. A type 2B (cardioinhibitory and asystole) response occurred in 61 patients. The duration of asystole was 12.8+/-10.6s (mean+/-SD; median 9, minimum 3, maximum 60). The head-up tilt test was repeated day after day: one session per day. The response became negative at the second session in 119 patients (54%); at session 3 in 47 (21%); at session 4 in 30 (13%); at session 5 in 15 (7%); at session 6 in 6 (3%); at session 7 in 2 (1%); at session 8 in 3 (1%). For all 222 patients the mean number of sessions in order to obtain a negative tilt test was 2.9 (SD 1.3; median 2). Only 25% of patients remained tilt-positive for three or more sessions. A negative tilt test was ultimately obtained in every patient. Follow-up data are available for 202/222 patients. The time span between the first and last tilt test was 11.1+/-10 months (median 8.8). Of these 202 patients, 163 remained free of any event (80.7%).     

Electrophysiologic testing in the evaluation of patients with syncope of undetermined origin

Thirty-two patients were prospectively evaluated for syncope (recurrent in 26 patients) with conventional neurologic and cardiovascular testing without elucidation of a cause. All patients underwent invasive electrophysiologic studies to assess sinus nodal function, atrioventricular conduction, and the inducibility of supraventricular and ventricular tachycardia (VT). Eleven patients (34%) were found to have laboratory-induced VT, 5 patients (15%) had evidence of sinus nodal dysfunction, 1 patient (3%) had infra-His atrioventricular block during atrial pacing, and 1 patient (3%) had probable quinidine-related VT. The remaining 14 patients had no detectable abnormalities during electrophysiologic study. After a mean follow-up period of 21.3 ± 1.2 months, 10 of the 11 patients with inducible VT were asymptomatic while receiving laboratory-directed antiarrhythmic therapy, and 1 patient died from ventricular fibrillation after discontinuing the chosen antiarrhythmic regimen. Five of the remaining 7 patients with an electrophysiologic abnormality were asymptomatic after implantation of a permanent pacemaker or alteration of previous drug therapy, or both. The 14 patients with a normal electrophysiologic study were treated empirically, with recurrent syncope occurring in 4 of these patients during the follow-up period. Invasive electrophysiologic studies provided a presumptive diagnosis in 56% of patients with syncope of undetermined origin. Previously unsuspected VT accounted for 61 % (11 of 18) of the detected abnormalities. Therapy specific for the electrophysiologic abnormality was usually successful in preventing recurrent syncope.     

The diagnostic value of ATP testing in patients with unexplained syncope.

A minority of patients with unexplained syncope has an increased susceptibility to adenosine triphosphate (ATP) injection. In these 'hypersensitive' patients, owing to its powerful cardiac and hypotensive effects, endogenous adenosine released under physiological and pathological conditions could trigger bradycardia and/or hypotension and cause syncope. This hypothesis still needs to be proven. However, there is some evidence that the ATP test identifies a group of patients with otherwise unexplained syncope with definite clinical features, absence of structural heart disease and benign prognosis. The mechanism of syncope is heterogeneous; indeed, in cases of electrocardiographic documentation of spontaneous syncope, either a long ventricular pause (mainly due to paroxysmal atrioventricular (AV) block) or no rhythm variations or even tachycardia were documented. ATP-positive patients have clinical features and mechanisms of syncope which are different from tilt-positive patients. Owing to its low positive predictive value, the ATP test is of little value in selecting treatment. A favourable outcome suggests a strategy of postponing treatment, in particular pacemaker therapy, until a definite diagnosis can be made by documenting a spontaneous syncopal relapse.     

Usefulness of midodrine in patients with severely symptomatic neurocardiogenic syncope: a randomized control study

INTRODUCTION: The efficacy of midodrine for the management of patients with neurocardiogenic syncope was assessed prospectively in a randomized control study. METHODS AND RESULTS: Patients who had at least monthly occurrences of syncope and a positive tilt-table test were included in the study. A total of 61 patients were randomly allocated to treatment either with midodrine or with fluid, salt tablets, and counseling. Midodrine was given at a starting dose of 5 mg three times a day and increased up to a dose of 15 mg three times a day when required. Midodrine was given during the daytime every 6 hours. Thirty-one patients were assigned to treatment with midodrine; the other 30 patients were advised to increase their fluid intake and were instructed to recognize their prodromes and abort the progression to syncope. Patients were followed-up for at least 6 months. A quality-of-life questionnaire was administered at the time of randomization and 6 months after. At the 6-month follow-up, 25 (81%) of 31 midodrine-treated patients and 4 (13%) of the 30 fluid-therapy patients had remained asymptomatic (P < 0.001). One patient had to discontinue taking midodrine due to severe side effects and another six patients experienced minor side effects that did not require drug discontinuation. CONCLUSION: Midodrine appeared to provide a significant benefit in patients with neurocardiogenic syncope. To prevent recurrence of symptoms, dose adjustments were required in about one third of patients.