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Figure 5 In March 1994, the presence of asymptomatic conduction disturbances on the surface electrocardiogram (ECG) prompted electrophysiologic testing in this 51-year-old woman with myotonic dystrophy. After the finding of a prolonged HV interval (70 ms), a pacemaker was implanted. During the first month after implantation, marker chains of paroxysmal high-degree atrioventricular (AV) block were recorded. In September 2000, 2:1 AV block was observed on the surface ECG. In March 2002, pacemaker dependency was demonstrated during temporary pacemaker inhibition, with underlying complete AV block, as shown on this ECG tracing (paper speed 25 mm/s).