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Commentary to: Christ M, Geier F, Popp S, et al., Diagnostic and prognostic value of high-sensitivity cardiac troponin T in patients with syncope. Am J Med 2015;128:161–170.e1.
During acute syncope management, cardiac causes (acute myocardial infarction (AMI), dysrhythmias or structural heart disease) are a concern and, hence, most patients have cardiac troponin (cTn) tests performed. While it can diagnose AMI, the role of cTn in identification of patients with underlying dysrhythmias or serious structural heart disease is unknown. With new high-sensitivity assays detecting even lower cTn levels, it is unclear if cTn levels can identify or predict non-cardiac serious conditions. This study examines the diagnostic accuracy of high-sensitivity cardiac troponin T (cTnThs) for cardiac syncope and its predictive value for short-term (30 days) or medium-term (180 days) adverse events.
This was a secondary analysis of pre-existing prospective observational data of adult syncope patients from a single-centre community hospital with cTnThs levels. The primary outcome was diagnosis of a cardiac syncope (dysrhythmias or structural heart disease). Secondary outcomes included: death, cardiac events, acute heart failure, pulmonary embolism, stroke, severe infection/electrolyte abnormalities, acute renal injury, haemorrhage, injuries, critical interventions (eg, pacemaker/defibrillator implantation), cardiopulmonary resuscitation or endoscopy and hospital readmissions. Diagnostic characteristics for the various cTn cut-points were calculated and multivariable Cox regression analysis was performed.
Three hundred and sixty patients were enrolled, median age was 70.5 years and 80 patients were diagnosed with cardiac syncope. Negative and positive predictive values for cardiac syncope at >14 ng/L (99th centile cut-off) were 0.90 and 0.40, and at >53 ng/L (assay cut-off) were 0.82 and 0.55, respectively. On multivariable analysis, cTnThs ≥14 ng/L was not found to be an independent predictor and on subgroup analysis, serial cTnThs (δ change ≥20%; or absolute change ≥10 ng/L) was not an independent predictor of 180-day events. Among non-cardiac syncope patients, there was a significant difference in event-free survival at 30-days and at 180-days between those below the 14 ng/L cut-off (91% and 84%, respectively) and above the cut-off (72% and 56%, respectively). No such difference was observed among patients with cardiac syncope.
This specific evaluation of cTnThs in acute management is an important contribution to the syncope literature. The authors conclude that cTn is not useful for diagnosing cardiac syncope and cTn levels or its changes are not independent predictors of 180-day adverse events. However, there are several limitations to these conclusions. A significant proportion of patients are older, which limits generalisability. Also, the study analyses cTn alone for cardiac syncope diagnosis. A multivariable analysis of clinical variables and cTn would have been more useful. Inclusion of events (eg stroke) not related to syncope and events at distant 180-days potentially could have rendered cTn not a useful predictor.1
Sun et al2 found abnormal troponin (>99th centile cut-off; contemporary assay) an independent predictor of 30-day syncope-specific events among older (≥60 years) patients. The predictive value of high-sensitive assay for 30-day syncope-specific events could have been assessed in the current study. The study shows that among cardiac syncope patients, cTn does not predict prognosis, raising the question of whether or not elevated cTn is an innocent bystander among these patients.3 However, the study found that among patients with non-cardiac syncope, higher cTn levels signify poor prognosis. As this was a single centre study with modest sample size, these findings must be confirmed by a prospective multicentre validation study.
Implications for practice
The study results raise questions regarding the role of cTn during acute syncope management and highlight the need for further studies to: (1) identify which patients need levels measured; (2) evaluate prognostic value of cTn for short-term syncope-specific events; (3) identify which subgroup of patients need serial troponin testing.
Competing interests None declared.
Provenance and peer review Commissioned; internally peer reviewed.