The intravenous adenosine test: a new test for the identification of bradycardia pacing indications? A pilot study in subjects with bradycardia pacing indications, vasovagal syncope and controls

Adenosine, adenosine- deaminase and implantable recorder outcome in syncopal patients

BACKGROUND

Adenosine test was proposed as a tool for identification of syncopal patients who benefit from pacemaker implantation. Aim of the study was to assess the relationship between adenosine levels, the outcome of adenosine test and results of implantable loop recorder (ILR) monitoring in patients with syncope.

METHODS

In 29 patients (mean age 59 ± 11 years, 15men, 14 women) with unexplained syncope ILR was implanted. In addition, adenosine test (intravenous injection of 20 mg adenosine bolus) and assays of plasmatic adenosine and adenosine-deaminase were performed.

RESULTS

Adenosine test was positive in 15 patients and negative in 14 patients. Patients with positive adenosine test had lower adenosine levels compared to patients with negative test (8,86 ± 2,07 ng/ml vs 15,18 ± 2,14 ng/ml, p = 0,04). No difference was observed in adenosine deaminase levels (16,35 ± 2,20 IU/l vs. 13,20 ± 2,48 IU/l, p = 0,40). There was a negative correlation between adenosine level and AVB duration during adenosine test (p = 0,04; R2 = 0,22). Patients with positive adenosine test had more frequent asystole during ILR monitoring than patients with negative test (9 pts vs 1pt, p = 0,005). Adenosine levels were lower in patients with asystolic syncope on ILR compared to vasodepressor syncope 8,20± 2,86 ng/ml vs 13,27± 7,26 ng/ml, p = 0,05).

CONCLUSIONS

Patients with positive adenosine test have decreased production of endogenous adenosine compared to patients with negative adenosine test. Positivity of adenosine test and low adenosine level in the peripheral blood were associated with more frequent asystolic episodes during ILR monitoring. This article is protected by copyright. All rights reserved.

Is the Adenosine Test Obsolete in the Clinical Assessment of Syncope of Unknown Origin?

Syncope is a common clinical condition affecting 50% of the general population; however, its exact pathophysiology and underlying mechanisms remain elusive. The adenosine test (ADT) has been proposed as a complementary diagnostic test in the work-up of syncope of unknown origin aiming to further elucidate the underlying pathogenetic mechanism of spontaneous syncope. Although ADT has not been endorsed by the recent European Society of Cardiology guidelines on syncope management, the use of a quick, safe and non-invasive test which can contribute to an accurate diagnosis and rationalised therapy, may deserve further consideration. This review summarises the evidence on the role of ADT in the investigation and management of syncope of unknown origin and highlights future perspectives in this area. The authors also analyse the current challenges and research targets on adenosine plasma levels and its receptors due to the involvement of the adenosine pathway in the ADT response.

Syncope: Case Studies

Syncope, or the sudden loss of consciousness, is a common presenting symptom for evaluation by neurologists. It is not a unique diagnosis but rather a common manifestation of disorders with diverse mechanisms. Loss of consciousness is typically preceded by a prodrome of symptoms and sometimes there is a clear trigger. This article discusses several cases that illustrate the various causes of syncope. Reflex syncope is the most common type and includes neurally mediated, vasovagal, situational, carotid sinus hypersensitivity, and atypical forms. Acute and chronic autonomic neuropathies and neurodegenerative disorders can also present with syncope.

The use of adenosine and adenosine triphosphate testing in the diagnosis, risk stratification and management of patients with syncope: current evidence and future perspectives

Syncope is a significant source of cardiovascular-related morbidity yet the etiology is frequently obscure and the identification of patients at highest risk is challenging. Adenosine (AD) and adenosine triphosphate (ATP) administrations have been suggested as potentially useful non-invasive tools in the diagnostic workup of patients with neurally-mediated or bradycardia-related syncope. It has been postulated that both compounds by modulating the autonomic innervation in the heart and exerting negative chronotropic and dromotropic effects in the conduction system, may unmask the mechanism of syncope. However, the clinical implications derived from the efficacy of both tests in the investigation of syncope remain unclear mainly due to inconclusive and occasionally contradictory results of published studies. This review article summarizes recent and past information in the use of ATP and AD in the investigation of syncope with emphasis on clinical trials. We present the current level of evidence for the use of these agents in clinical practice, identify areas where further research is warranted and highlight the future perspectives of these agents as complements to an accurate risk-stratification of patients with syncope.

Treatment of unexplained syncope: a multicenter, randomized trial of cardiac pacing guided by adenosine 5'-triphosphate testing

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.