Mechanisms of pain associated with internal defibrillation shocks: results of a randomized study of shock waveform.
BACKGROUND
Shock pain has limited the acceptance of the implantable atrial cardioverter and is a complication of ventricular implantable cardioverter-defibrillator therapy. Rounding off of the peak of a shock waveform reduces pain. Whether the pain reduction results from reduction in the peak voltage or from the rounding has not been established. In other words, does reducing the extreme dV/dt (voltage derivative) of the conventional truncated exponential capacitive discharge waveform reduce pain?


OBJECTIVE
The purpose of this study was to compare the relative contributions of peak voltage and waveform shape to pain.


METHODS
We compared rounded and conventional waveforms with equal peak voltages. Eighty-five shocks of 50 to 500 V were delivered to 10 patients requiring atrial cardioversion for persistent atrial fibrillation. The patient touched an analog pain scale (0-15 cm) and orally reported a pain score on a scale from 0 to 5. An observer scored thoracic contractions on a scale from 0 to 5.


RESULTS
No differences between the rounded and conventional waveform on any scale were noted for either univariate or multivariate analyses. However, all three response scales were strongly predicted by voltage with r(2) = 0.77 (oral), r(2) = 0.86 (analog), and r(2) = 0.85 (contraction) after correcting for patient variability and including a log voltage term.


CONCLUSIONS
Patient pain perception was determined primarily by waveform peak voltage and not by the rounding, per se.
Istituto di Cardiologia, Università di Bologna, Azienda Ospedaliera S. Orsola-Malpighi, Bologna, Italy.
Giuseppe
G
Boriani
Mauro
M
Biffi
Paolo
P
Silvestri
Cristian
C
Martignani
Cinzia
C
Valzania
Igor
I
Diemberger
Chris
C
Moulder
Gabriel
G
Mouchawar
Mark
M
Kroll
Angelo
A
Branzi
D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000628:therapy*; D017147:Defibrillators, Implantable; D025802:Electric Capacitance; D004554:Electric Countershock / Q000009:adverse effects* / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D010147:Pain Measurement; D011446:Prospective Studies