Atrial tachysystole (flutter?) with apparent exit block.
D001282:Atrial Flutter / Q000175:diagnosis; D003937:Diagnosis, Differential; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000150:complications*; D006801:Humans; D008875:Middle Aged; D013614:Tachycardia, Paroxysmal / Q000150:complications* / Q000175:diagnosis