OVERLAPPING SEQUENTIAL PULSES - A NEW WAVE-FORM FOR TRANSTHORACIC DEFIBRILLATION

Background A directionally changing shock electrical vector could faci litate defibrillation by depolarizing myocytes with different orientat ions vis-a-vis the shock field. Such a changing vector can be achieved by a new waveform for transthoracic defibrillation: overlapping seque ntial pulses. Our purpose was to evaluate this waveform. Methods and R esults Ventricular fibrillation was induced in closed-chest dogs. Sing le and overlapping truncated exponential waveform pulse shocks were th en administered from self-adhesive chest electrodes. Single pulse (con trol) shocks were 7.5-millisecond duration, while the sequential overl apping pulse shocks, using two different pathways, consisted of two pu lses, each 5.0-millisecond duration; the second pulse began 2.5 millis econds after the start of the first pulse and ended 2.5 milliseconds a fter the end of the first pulse. Thus, the total duration of the seque ntial overlapping shock was 7.5 milliseconds. During the overlap phase (2.5 milliseconds), the electrical vector orientation is the summatio n of the individual vectors. Two different electrode placements and co rresponding electrical vector orientations were studied: group 1 (n=14 ), left lower chest to right upper chest (pulse 1), overlapped by righ t lower chest to left upper chest (pulse 2), with the sequence then re versed; and group 2 (n=11), left chest to right chest (pulse 1) overla pped by dorsal (vertebral column) to ventral (sternum) (pulse 2) with the sequence then reversed. At voltages equivalent to energies of 50, 100, and 150 J, the sequential overlapping pulse shocks achieved highe r success rates than the single pulse shocks: At the low energy, 50 J, single pulse shock success rates were 0% (group 2) and 14% (group 1), while the overlapping pulse shocks achieved success rates of 39% (gro up 2) and 55% (group 1) (P<.05). Similarly, at the highest energy test ed, 150 J, single pulse shock success rates were 45% (group 2) and 61% (group 1), while the overlapping pulse shock success was 91% (group 2 ) and 95% (group 1) (P<.05). In a third group of dogs (n=3), intracard iac plunge electrodes placed orthogonally in the septum showed that th e orthogonal components of intracardiac voltage gradient change varied markedly during the three phases of the sequential overlapping shocks , demonstrating the changing direction of the net electrical vector as the shock proceeded. In a fourth group of dogs (n=5), short-duration (2.5-millisecond) single pulse shocks were compared with longer 7.5-mi llisecond single pulse shocks and with the sequential overlapping puls e shacks, all at equivalent energies. Despite substantially higher cur rent flow, the 2.5-millisecond-duration single pulse shocks were not m ore effective than 7.5-millisecond single pulse shocks, and both 2.5- and 7.5-millisecond duration single pulse shocks had markedly inferior success rates compared with the sequential overlapping pulse shocks. Conclusions Sequential overlapping pulse shock waveforms facilitate de fibrillation compared with single pulse shocks of the same total energ y. This is due at least in part to the changing orientation of the ele ctrical vector during the multiple pulse shock.