Ventricular fibrillation induction using nonsynchronized low energy external shock during rapid ventricular pacing: method of induction when fibrillation mode of ICD fails

Is external defibrillation an electric threat for bystanders?

BACKGROUND

Safety precautions during defibrillation and cardioversion are generally taken very seriously. The actual hazard for bystanders and rescuers, however, has rarely been investigated. Recently, continuing chest compressions during defibrillation has been suggested to improve outcome from cardiac arrest. This article is to review reports on electric shocks to persons other than patients and to discuss the pertinent biomedical principles.

METHODS

Systematic search in medical literature databases and consecutive hand-search of reference lists.

RESULTS

A total of 29 adverse events are reported in the medical literature; seven due to accidental or intentional defibrillator misuse, three due to device malfunction, four during training/maintenance procedures, and 15 during regular resuscitation efforts. Tingling sensations and minor burns are frequently reported consequences of inadvertent shocks. There are no accounts on immediate life-threatening conditions or long-term disability in rescuers/bystanders inflicted by defibrillation/cardioversion of a patient. Discharging a defibrillator directly to a healthy person's chest can be lethal.

CONCLUSIONS

External electric therapy is likely to be safer than traditionally assumed, especially with self-adhesive thoracic electrodes. Sound clinical experiments are urgently needed before safety measures are revised.

Low voltage direct current delivered through unipolar transvenous leads: an alternate method for the induction of ventricular fibrillation

The induction of VF during testing of an ICD may not always be possible using either burst pacing or high energy T wave shocks. The purpose of this study was to evaluate the effectiveness of low energy DC stimulation for inducing VF in a porcine model. The VFT was measured using constant voltage stimuli and a step-up method in ten anesthetized pigs (25-30 kg). Stimuli of different durations (0.5, 1.0, 2.0 s) were delivered (unsynchronized) between a right ventricular apical coil and a subcutaneous test can. Current was measured from the voltage drop across a series resistor (10 omega). With anodal stimulation, VF required 6.4 +/- 0.2 V compared to 13.8 +/- 0.6 V with cathodal stimulation (P < 0.001). The current required to induce VF (measured 10 ms after the stimulus onset) was 58.3 +/- 2.2 mA with anodal stimulation and 119.3 +/- 4.7 mA with cathodal stimulation (P < 0.001). Stimulus duration did not significantly influence the voltage or current required for VF induction. In 6 of the 10 pigs, synchronizing a 0.5-second stimulus to the R wave did not significantly alter the VFT compared to same stimulus synchronized to mid-upslope of the T wave. The results indicate that VF can be consistently induced through transvenous electrodes by passing unsynchronized DC for 0.5-2 seconds. The induction of VF required about 50% less current and voltage with anodal stimulation. It should be possible to induce VF with the DC voltage available from the internal battery source of an ICD.

Temperature controlled RF ablation in canine ventricle and coronary sinus using 7 Fr or 5 Fr ablation electrodes

The safety and lesion volume of temperature controlled radiofrequency ablation (TCRFA) in the right ventricle (RV), left ventricle (LV), and coronary sinus (CS) comparing long 5 Fr to standard tip electrodes have not been previously reported. In 10 canines, TCRFA was delivered at a 70 degrees C set point for 30 seconds. Lateral and septal RV lesions were made with either a 5 Fr/5 mm or 7 Fr/4 mm tip. Lateral and septal LV lesions were made with either a 5 Fr/7 mm or 7 Fr/4 mm tip. Proximal and distal CS lesions were made with either a 7 Fr/4 mm, 5 Fr/5 mm or 5 Fr/7 mm tip. Gross and histologic examination of the lesions was completed. Lesion size, tip temperature and power required are related to electrode surface area (SA) when ablating in the RV, LV or CS. 5 Fr/7 mm tips (SA = 36 mm2) tended to create larger lesions than 7 Fr/4 mm tips (SA = 29 mm2) in the LV. 7 Fr4 mm tips tended to create larger lesions than 5 Fr/5 mm tips (SA = 26 mm2) in the RV. 7 Fr/4 LV lesions exceeded 7 Fr/4 mm RV lesions due to thicker LV walls. In the CS, 5 Fr/7 mm tips tended to create the largest lesions. In the RV, LV and CS, tips with larger SA tended to have lower temperatures and require higher power. No high temperature or high impedance shut-downs were observed. In conclusion, varying 5 Fr tip length can safely produce larger or smaller lesions compared to those created with 7 Fr/4 mm tips.

Transcutaneous T wave shock: a universal method for ventricular fibrillation induction

Our objective was to develop a universal noninvasive method for VF induction. ICD implantation requires VF induction. Conventional rapid ventricular stimulation may fail to induce VF. Some ICDs can deliver low energy shocks on the T wave to induce VF. We hypothesized that an external dual chamber pacemaker and an external defibrillator could be configured to allow reliable VF induction with any ICD system. A surface ECG signal was delivered to the atrial channel of an external dual chamber DDD pacemaker. The 'AV' delay was adjusted so that the ventricular output of the pacemaker was delivered to an external defibrillator synchronized to deliver 5-50 J. Twenty-six patients at ICD implant or follow-up had VF induced in native rhythm (sinus rhythm or atrial fibrillation), or during a ventricular pacing train (3-8 beats at cycle length 500-880 ms). VF was successfully induced in 14 of 25 (56%) patients in native rhythm; and in 16 of 17 (94%) patients during pacing (P = 0.013). VF induction success rate was 36% in native rhythm (31/86 attempts) and 88% during pacing (69/78 attempts) (P < 0.001). The 'R' to shock interval was 269 +/- 31 ms in native rhythm and 257 +/- 48 ms during pacing. Energy delivered from the external defibrillator was 19 +/- 3 J in native rhythm and 21 +/- 6 J during pacing. We concluded that VF induction by synchronizing a small external shock to the T wave is a fast, effective way to reliably ensure arrhythmia induction with any ICD at implant or follow-up. This method is more successful during pacing than in sinus rhythm.