A Case of Cardiac Amyloidosis Whose Exercise Intolerance Was Caused by Loss of Bi-Ventricular Pacing after Atrial Contractions within Pacemaker Refractory Period

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A 68-year-old man presented with congestive heart failure (NYHA III) with QRS morphology of left bundle branch block. Systemic amyloidosis with cardiac involvement was pointed out 7 years ago. A Medtronic CRT-D device was implanted because of dyssynchronous left ventricular motion. Four months after implantation, the patient had recurrent episodes of faintness during exercise. Faintness was coincident with sudden prolongation of a P-P interval from 600 ms to 1100 ms at the peak exercise. It was due to sinus pause followed by a back-up pacing of nonrate responsive DDD pacing at 60/min with rate adaptive AV delay (280 ms to 180 ms). The pacing parameters were changed so that the symptom was resolved. Sixteen months later, the patient developed general fatigue during exercise. Exercise intolerance was apparently due to bi-ventricular pacing failure, but this was not shown at rest. Intra-cardiac ECG during exercise showed a premature atrial contraction and/or a non-competitive atrial pacing (NCAP) within post-ventricular atrial refractory period (PVARP), followed by aborted ventricular pacing. Conducted own QRS appeared to resume ventricular dyssynchrony. Symptom was improved after NCAP was turned off and PVARP was shortened. This case is unique because of exercise-induced loss of bi-ventricular pacing, which was not due to shortening of own AV conduction. It was useful to examine intra-cardiac ECG during exercise in detail.