Transient data stream dissociation in computerized data acquisition system masquerading as a sensing abnormality.

During testing of a CPI model 1715 ICD, an apparent sensing abnormality was noted following shock delivery for VF. Close inspection of the recording prior to the defibrillation attempt revealed that the surface leads spontaneously lost 848 ms of data while the event marker was unaffected. Computer simulations revealed that an inadequate buffer size for the amplified (surface ECG) data was the likely source of data loss. It is important to recognize that a discordance between surface leads and event marker may represent an abnormality in the data acquisition system and simulate an ICD or lead malfunction.