Head-Up Tilt in Patients with Bifascicular Block
ABSTRACT & COMMENTARY
Synopsis: In this population, head-up tilt had such a poor specificity that changes in the protocol to improve sensitivity would unlikely be helpful.
Source: Englund A, et al. Circulation 1997;95:951-954.
Syncope remains a perplexing problem that continues to challenge clinicians. Englund et al evaluated the value of head-up tilt testing in patients with bifascicular block. Twenty-five patients with bifascicular block and syncope who had completed a negative noninvasive evaluation formed the study group. The noninvasive evaluation included a history and physical examination, a symptom-limited exercise test, a two-dimensional cardiac echo with Doppler examination, a 24-hour ambulatory ECG, and an electrophysiologic study. The authors started with a group of 50 patients, but a probable cause was identified through this protocol in 25. A group of 25 age- and gender-matched subjects with bifascicular block but without a history of syncope or dizzy spells formed the control group. The mean ages were 67 and 69 years in the syncope and control groups, respectively. Slightly more than half the patients in both groups had identifiable structural heart disease. Patients in both groups underwent a tilt table study using a standard protocol that involved 45 minutes of 60° head-up tilt with continuous noninvasive blood pressure and ECG monitoring. After the tilt study, but without regard to the results, patients with a clinical history of syncope were offered implantation of a VVI pacemaker with a feature that allowed documentation of spontaneous bradycardia. Nineteen of the 25 patients with syncope accepted pacemaker implantation. Both groups were then followed at regular intervals in an outpatient clinic.
Among the syncope patients, seven of 25 (28%) had a positive tilt test, compared to eight of 25 (32%) in the control group. The patients in the syncope group with positive studies stated that their prior symptoms were replicated by the study. Symptoms during the test occurred at 33 ± 11 minutes in the patients with syncope and at 22 ± 8 minutes in the control group. Differences in the patterns of blood pressure and heart rate drop were not seen between the two groups. During 20-45 months of follow-up, six of 25 patients in the syncope group had recurrent symptoms, but bradycardia as the cause of symptoms could be excluded in five of the six. Three of these had manifest vasodepressor or mixed responses at the prior tilt study. One additional syncope patient with a positive tilt study had a heart rate of less than 30 bpm for more than six seconds documented by his pacemaker, but he reported no symptoms. None of the control patients developed symptoms during follow-up.
The authors conclude that their study raises serious concerns regarding the specificity of head-up tilt testing in patients with bifascicular block. As a result, they recommend conservative use of head-up tilt in this population.
COMMENT BY JOHN P. DiMARCO, MD, PhD
Evaluation of patients with syncope remains an often unrewarding exercise. In recent years, head-up tilt testing has become widely accepted as a useful diagnostic tool for evaluating patients with syncope of unknown origin (for a recent review, see Benditt DG, et al. J Am Coll Cardiol 1996;28:263-275). Without question, head-up tilt testing has greatly improved our understanding of the mechanisms underlying a common etiology for syncope. However, as exemplified in this article, many clinicians perceive significant limitations in the clinical value of these tests in individual patients.
A number of factors influence the sensitivity and specificity of tilt testing as a diagnostic tool. The duration and angle of tilt, the type of blood pressure monitoring used, the age and cardiac diagnosis of the patient, and the use of pharmacologic provocation are all important considerations that can influence study results. In this article, Englund et al used a very conservative test protocol that was designed to be as specific as possible. Despite this, 32% of a control group of patients had positive study results. The results in the patients with syncope were also of little value. A positive study was uncommon and did not effectively indicate which patients would experience a recurrence. Thus, in this population, head-up tilt had such a poor specificity that changes in the protocol to improve sensitivity would unlikely be helpful.
These authors have also evaluated the role of electrophysiologic studies in patients with bifascicular block and syncope (J Am Coll Cardiol 1995;26:1508-1525), and their data have raised questions about the value of that type of evaluation as well. Based on their provocative findings, we can only humbly admit that evaluation of a transient phenomenon like syncope, which can have multiple potential causes, remains a difficult and often frustrating proposition. However, the observations reported here strictly apply only to relatively older patients with bifascicular block, and a different utility may be seen in other patient groups.