The Expectation Effect and Cardiac Pacing for Refractory Vasovagal Syncope

Forest plot of primary study and summary odds ratios for recurrent syncope. Studies are ordered, based on the control therapy and based on double-blind trial methodology. For each study, the random effects odds ratios are indicated by black squares, and horizontal lines represent the 95% confidence intervals. The area of the black square is proportional to the amount of ‘statistical information’ contributed by the trial. Odds ratios less than unity favor the strategy of permanent cardiac pacing. The diamond at the bottom of each category and overall represents the summary odds ratio (OR) with 95% confidence intervals. The results favor cardiac pacing in Groups 1 and 2, but not Group 3.

Forest plot of primary study and summary odds ratios for recurrent syncope, restricted to patients with cardioinhibitory response to tilt table testing. The random effects odds ratios (OR) and 95% confidence intervals for the development of recurrent syncope in patients with a cardioinhibitory tilt table response are based on reports from 6 trials involving patients from Groups 1 and 3 only. The results mirror those of the overall meta-analysis with benefit of cardiac pacing seen in Group 1 but not Group 3. The test of interaction between groups was significant (P=.001). The confidence intervals for Group 3 are wide, and modest treatment effects cannot be excluded.

Estimation of the expectation response of cardiac pacing in preventing recurrent syncope. Shown are the odds ratios (ORs) (based on the Peto Method) and 95% confidence intervals (CI) for the comparisons of active cardiac pacing versus no therapy (Group 1), “inactive” versus active cardiac pacing (Group 3), and the synthesized results for “inactive” cardiac pacing versus no therapy. Inactive cardiac pacing refers to pacemakers programmed to sensing only. Note, the results for Group 3 are simply the reciprocal of the results shown in Table 2 as the emphasis of the comparison is reversed. The horizontal line drawn at the OR of 1.0 indicates the null hypothesis of no difference between groups. Estimates to the left of this line represent treatment better and estimates to the right represent control better. Note that the controls will be no therapy for the first and third comparison and active pacing for the middle comparison. The bottom comparison represents the synthesized “expectation response” as this is the effect of inactive cardiac pacing (functioning in sensing mode only) versus no therapy. The expectation response alone reduces the odds of syncope by 84% (OR 0.16, 95% CI, 0.06 to 0.40, P=.0001). PPM=permanent pacemaker.