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A patient with complete heart block due to ankylosing spondylitis exhibited an unusually brisk increase in ventricular rate with exercise. Despite broad ventricular (QRS) complexes, His bundle electrograms demonstrated a His deflection before each QRS complex and thus established the level of atrioventricular (A-V) block to be proximal to or localized to the His bundle. A junctional pacemaker accounted for the brisk response to exercise, atropine, or isoproteronol. Left bundle branch block pattern and prolongation of infranodal conduction time (H-Q) suggested additional disease involving the His bundle and/or right fascicle. Wide-spread disease affecting A-V nodal and infranodal conduction was compatible with pathologic changes seen in this disease. Because the pacemaker was able to respond to stress promptly and with appropriate increase in heart rate, the patient appeared not to warrant pacemaker implantation in his present state.
David B. Harvey (Wed,) studied this question.