THE EFFECT OF POLARITY OF THE INITIAL PHASE OF A BIPHASIC SHOCK WAVE-FORM ON THE DEFIBRILLATION THRESHOLD OF PECTORALLY IMPLANTED DEFIBRILLATORS

The effect of initial phase polarity on the DFT of two pectorally impl anted biphasic ICDs was tested in a randomized, prospective manner at the time of implantation. Twenty-two consecutive patients with VT or V F who received either the Medtronic PCD 7219C jewel device (10 patient s) or PCD 7219D Jewel device (12 patients) were studied. DFT testing w as performed in a standard step-down manner. Both initial phase polari ties-initial defibrillation current flowing from active can/SVC coil ( +/- subcutaneous patch) to the RV coil (RV-) or from RV coil to active can/SVC coil (RV+)-were tested in random order. The mean DFT achieved with RV+ compared with RV- was lower for the 7219C patient group (6.6 +/- 3.1 vs 10.8 +/- 5.5 J;P = 0.007). A similar trend was observed fo r the 7219D group, though the difference did not reach statistical sig nificance (12.0 +/- 4.0 vs 16.3 +/- 7.3 j;P = 0.07). Seven of the 10 p atients in the 7219C group had a lower DFT with RV+, while the initial phase polarity made no difference in 3. in the 7219D group, 7 patient s had a lower DFT using RV+, 2 patients had a lower DFT using RV-, and the initial phase polarity made no difference in 3. in conclusion, th is study demonstrates that changing the polarity of the initial phase of a biphasic shock waveform can have a significant impact on the DFT achieved at the time of ICD implantation.