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Background— The origin of 40% of syncope cases remains unknown even after a complete diagnostic workup. Previous studies have suggested that ATP testing has value in selecting successful therapy. This patient-blinded, multicenter, randomized superiority trial tested whether, in patients with syncope of unknown origin, selecting cardiac pacing in those with a positive ATP test leads to fewer recurrences than those who do not receive pacing. Methods and Results— From 2000 to 2005, 80 consenting patients (mean age, 75.9±7.7 years; 81% women; 56% without diagnosed structural heart disease) with syncope of unknown origin and atrioventricular or sinoatrial block lasting >10 seconds (average, 17.9±6.8 seconds) under ATP administration (20-mg IV bolus) were recruited from 10 hospitals, implanted with programmable pacemakers, and randomized to either active pacing (dual-chamber pacing at 70 bpm) or backup pacing (atrial pacing at 30 bpm). Patients were followed up regularly for up to 5 years for any syncope recurrence, the primary outcome. Mean follow-up was 16 months. Syncope recurred in 8 of 39 patients (21%) randomized to active pacing and in 27 of 41 (66%) randomized to backup pacing (control), yielding a hazard ratio of 0.25 (95% confidence interval, 0.12–0.56). After recurrence, the 27 recurrent control patients were reprogrammed to active pacing, and only 1 reported subsequent syncope. Conclusion— This study suggests that, in elderly patients with syncope of unknown origin and positive ATP tests, active dual-chamber pacing reduces syncope recurrence risk by 75% (95% confidence interval, 44–88). Clinical Trial Registration— URL: http://www.controlled-trials.com/ISRCTN00029383 . Unique identifier: ISRCTN00029383.

Background The origin of 40% of syncope remains unknown even after a complete diagnostic work-up. Previous studies have suggested that adenosine 5’-triphosphate (ATP) testing has value in selecting successful therapy. This patient-blinded, multicenter, randomized superiority trial tested whether, in patients with syncope of unknown origin (SUO), selecting cardiac pacing in those with a positive ATP test results in fewer recurrences than those who do not receive pacing. Methods and Results From 2000 to 2005, 80 consenting patients (mean age 75.9±7.7 years; 81% women; 56% without diagnosed structural heart disease) with syncope of unknown origin and atrioventricular or sinoatrial block lasting longer than 10 seconds (average 17.9±6.8 seconds) under ATP administration (20 mg IV bolus) were recruited from 10 hospitals, implanted with programmable pacemakers and randomized to either active pacing (dual-chamber pacing at 70 beats per minute (bpm) or backup pacing (atrial pacing at 30 bpm). Patients were followed regularly for up to five years for any syncope recurrence, the primary outcome. Mean follow-up was 16 months. Syncope recurred in eight (21%) of 39 patients randomized to active pacing and in 27 (66%) of 41 randomized to backup pacing (control), yielding a hazard ratio of 0.25 (95% CI: 0.12–0.56). After recurrence, the 27 recurrent control patients were reprogrammed to active pacing and only one reported subsequent syncope. Conclusions This study suggests that, in elderly patients with syncope of unknown origin and positive ATP tests, active dual-chamber pacing reduces syncope recurrence risk by 75% (95% confidence interval, 44–88).

In order to assess the feasibility of microsatellite primers as markers for genomic instability, we conducted a study of DNA stability in cauliflower callus. A protocol is described for the rapid screening of a large number of putative variant calli and plants. Genomic DNA is isolated and screened by microsatellite primers. We believe that inter-simple sequence repeat PCRs can conveniently detect and measure common genetic events underlying plant genomic instability. These include deletions, amplifications, translocations, insertions, recombination or chemical alterations. Our results indicate that instability occurred in an early step in the process of callogenesis. The technique is fast, reproducible, and is a new application for ISSR markers.