Investigation into voltage breakdown in glyceryl trinitrate patches

There are clinical reports of explosions occurring in glyceryl trinitrate (GTN) patches left on patients who are defibrillated and it is widely recommended that such patches are removed before attempting defibrillation. We devised an experimental set up that simulated the electrical conditions under which human defibrillation is conducted, thus making possible accurate measurements of defibrillator wave form. No problems occurred with GTN patches that incorporated a plastic backing. However, with GTN patches that incorporated a metal mesh backing, an explosive effect was consistently observed when current from the defibrillator electrode flowed through the metallic backing. The GTN paste in the patches was unaffected and therefore, we conclude that the apparent explosions reported are solely due to voltage breakdown as the paddle voltage is close to 3 kV resulting from the 360 J of energy. Our results emphasise the need for good technique during defibrillation to avoid current flow through such patches. In addition, our results have implications for the design of patches used for the transcutaneous delivery of drugs.