Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (60 page)

   ECG is diagnostic for arrhythmia-related syncope if the following are present: sinus bradycardia ≤40 bpm or persistent sinus pauses ≥3 seconds, alternating left and right bundle branch blocks, pacemaker/ICD malfunction with pauses, Mobitz II or third-degree AV block, ventricular tachycardia.

   Low-risk patients should not undergo further evaluation unless episodes are recurrent.

   
Echocardiography
is recommended when underlying structural heart disease (i.e., hypertrophic cardiomyopathy, aortic stenosis, dilated cardiomyopathy) is known or is suspected by exam or secondary findings and will help in risk stratification. Only the presence of severe aortic stenosis, obstructive tumor (atrial myxoma), aortic dissection, and cardiac tamponade are considered diagnostic echocardiographic findings for syncope.

   Exercise testing is appropriate with exertional syncope and may reveal arrhythmogenic etiologies. Coronary ischemia rarely presents as syncope, but stress testing is recommended in patients with prior coronary artery disease presenting with syncope.

   Twenty-four– to forty-eight– hour Holter monitors are not recommended for outpatients, as the sensitivity is low (1–3%). Patients with symptoms on a frequency of ≤4 weeks can be considered for external event recorders or implantable loop recorders.

   Invasive electrophysiological study (EPS) is expensive and of very low diagnostic yield (3%) in syncope without structural heart disease. In patients with structural heart disease, EPS is positive in 50% and should be performed in individuals with known coronary disease and high-risk ECG features.

   For orthostatic or neutrally mediate syncope, tilt table testing may be performed. This should be done in patients with only intermediate suspicion as the sensitivity is variable (25–75%) but specificity is high 90%, with negative tilt table testing having excellent reproducibility (>90%).

Suggested Readings

Kapoor WN. Evaluation and outcome of patients with syncope.
Medicine (Baltimore).
1990;69:160.

Reed MJ, Newby DE, Coull AJ, et al. The ROSE (risk stratification of syncope in the emergency department) study.
J Am Coll Cardiol.
2010;55:713.

Strickberger SA, Benson DW, Biaggioni I, et al. AHA/ACC Scientific Statement on the evaluation of syncope: from the American Heart Association Councils on Clinical Cardiology, Cardiovascular Nursing, Cardiovascular Disease in the Young, and Stroke, and the Quality

of Care and Outcomes Research Interdisciplinary Working Group; and the American College of Cardiology Foundation: in collaboration with the Heart Rhythm Society: endorsed by the American Autonomic Society.
Circulation.
2006;113:316.

Task Force for the Diagnosis and Management of Syncope, European Society of Cardiology (ESC), European Heart Rhythm Association (EHRA), et al. Guidelines for the diagnosis and management of syncope (version 2009).
Eur Heart J.
2009;30:2631.

SUDDEN CARDIAC ARREST

   Definition

   The sudden cessation of cardiac activity and hemodynamic collapse due to sustained ventricular arrhythmia.

   Formal definition has been difficult to define due to the fact up to one third of cases not witnessed. Absence of noncardiac pathology and presumed sudden loss of pulse are the most agreed upon criteria.

   Up to 15% of overall mortality in industrialized countries, with ≥300,000 cases/year.