technetium-tc-99m-tetrofosmin and Syncope

Whether tachycardia-dependent paroxysmal AV block, an uncommon complication of exercise stress testing in patients with infranodal conduction disturbances, can result from acute ischemia of the conduction system is still speculative, and is based on post-hoc evidence of right coronary artery disease and abolition of block after coronary angioplasty.. In two patients, from a database of 3000 undergoing nuclear exercise stress testing, transient paroxysmal AV block developed 1-4 minutes after the injection of the radionuclide agent. Nuclear perfusion imaging demonstrated stress-induced ischemia of the posteroseptal segments, which corresponds to the anatomical region of the His bundle, and perfusion recovery in the images obtained at rest. Angiography disclosed critical narrowing of the right coronary artery in both cases.. Nuclear myocardial perfusion imaging provides noninvasive evidence that transient ischemia of the posteroseptal segment, anatomically corresponding to the His bundle, can result in paroxysmal AV block in patients with severe right coronary artery and chronic infranodal conduction disturbances. The demonstration of the underlying pathophysiological mechanism is useful for selecting the most effective treatment strategy.

Topics: Acute Disease; Aged; Angioplasty, Balloon, Coronary; Coronary Angiography; Coronary Disease; Exercise; Exercise Test; Heart Block; Heart Conduction System; Humans; Male; Middle Aged; Myocardial Ischemia; Organophosphorus Compounds; Organotechnetium Compounds; Radiopharmaceuticals; Syncope; Tomography, Emission-Computed, Single-Photon

Topics: Aged, 80 and over; Bile Ducts; Dilatation; Disease Progression; Echocardiography; Humans; Incidental Findings; Liver; Male; Myocardial Perfusion Imaging; Organophosphorus Compounds; Organotechnetium Compounds; Pancreatic Neoplasms; Perfusion; Purines; Pyrazoles; Syncope; Tomography, Emission-Computed, Single-Photon; Ventricular Dysfunction, Left