Background: The estimated total annual cost of syncope-related hospitalizations in the year 2005 was about $2.4 billion with a mean cost of $5,400 per hospitalization. Syncope of cardiac etiology has 18-33% mortality in comparison to 0-12% with non-cardiac etiology. We sought to evaluate the role cardiac biomarkers in patients presenting with syncope to evaluate their role in triage and predicting adverse cardiovascular outcomes.
Methods: We performed a systematic review and meta-analysis of all studies evaluating the role of B-type natriuretic peptide (BNP), N-terminal pro-BNP (NT-proBNP), cardiac troponin-T and I (TnT, TnI) and highly sensitive TnT (hsTnT) in patients presenting with syncope. We excluded pediatric studies, studies without a control group and non-English literature. Data on demographics, clinical details, comorbidities, laboratory parameters and imaging details were abstracted from the selected studies. Primary outcomes assessed were all-cause mortality and major acute cardiac and cerebrovascular events (MACCE). Secondary outcomes included cardiac and non-cardiac etiology and need for cardiac or non-cardiac interventions. Pooled risk ratio (RR) with 95% confidence interval (CI) was calculated using Mantel-Haenszel random effects model.
Results: In the period from 1946 to September 2015, 624 studies were reviewed with 13 meeting our inclusion criteria (3 retrospective, 10 prospective observational). A total of 3763 patients, with 2628 (69.8%) admitted to the hospital were included. Mean age for the total cohort was 68.1 ± 24.5 years and included 201 (55.8%) males. BNP, NT-proBNP, TnT, TnI and hsTnT were assessed in 5, 1, 2, 3 and 2 studies respectively. Common comorbidities for the total cohort included hypertension 837/1846 (45.3%), diabetes 140/779 (18.0%), coronary artery disease 466/2007 (23.2%), valvular heart disease 83/1637 (5.1%), heart failure 216/2007 (10.8%), history of arrhythmias 129/679 (19.0%) and prior strokes/transient ischemic attacks 42/419 (10.0%). Etiology for syncope was reported in 1340 patients, with 316 (23.6%) and 909 (76.4%) patients having cardiac and non-cardiac causes respectively. Three and two studies reported mortality and MACCE as outcomes. Due to the low number of studies, the I2 statistic revealed a high heterogeneity (87-91%). Pooled RR for mortality (RR 12.4, 95% CI 0.4-363.6) and MACCE (RR 4.6, 95% CI 0.3-70.8) did not show any difference in cohorts with and without cardiac biomarker elevation. The data was insufficient to assess for the secondary outcomes of etiology and interventions.
Conclusions: Cardiac biomarker elevation did not portend a higher mortality or MACCE in patients with syncope. The current data however is insufficient to differentiate etiology of syncope in these patients. The conclusions of our study need further validation in well-designed randomized studies due to the limitations in the current body of evidence.