Exercise-induced paroxysmal atrioventricular block during nuclear perfusion stress testing: evidence for transient ischemia of the conduction system.
BACKGROUND
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.


RESULTS
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.


CONCLUSIONS
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.
Finzi
A
A
Department of Cardiology, Ospedale Maggiore di Milano, IRCCS.
Bruno
A
A
Perondi
R
R
D000208:Acute Disease; D000368:Aged; D015906:Angioplasty, Balloon, Coronary; D017023:Coronary Angiography; D003327:Coronary Disease / Q000175:diagnosis / Q000628:therapy; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D006327:Heart Block / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000628:therapy; D006329:Heart Conduction System / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000628:therapy; D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D013575:Syncope / Q000000981:diagnostic imaging / Q000503:physiopathology; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C078700:technetium tc-99m tetrofosmin