This tracing shows first a fusion beat of a ventricular paced and a conducted sinus complex. Note the intermediate QRS morphology of the first complex as compared to that of a sinus complex (second complex) and the 4th complex which is a paced ventricular complex. The pacemaker is not sensing which is normal for this pacemaker when the magnet is applied. The second stimulus does not capture the ventricle as it falls on the T wave, as is the case of the 4th, which falls in the ST segment and is not abnormal. What is grossly abnormal is the 5th and 6th spikes that fail to capture well out side of the refractory period of the ventricle.

Dr. M. Rosengarten M.U.H.C.