Radiofrequency Ablation with an Enhanced-Irrigation Flexible-Tip Catheter versus a Standard-Irrigation Rigid-Tip Catheter.

BACKGROUND: The flexible-tip irrigated ablation catheter Cool Flex™ (St. Jude Medical, St. Paul, MN, USA) was introduced to enhance cooling of the catheter-tissue interface and to conform to endocardial surface with better contact. Little is known about the performance of such catheter design compared to the widely used rigid-tip catheters. METHODS: In a thigh muscle preparation, ablation using the flexible-tip and rigid-tip catheters was performed in seven pigs across a range of ablation settings and catheter orientation. Postprocedure, the thigh muscle was stained with 2,3,5-triphenyltetrazolium-chloride injected into the femoral artery. The muscle was excised, fixed with formalin, and examined grossly. RESULTS: A total of 196 lesions (95 flexible tip, 101 rigid tip) were evaluated. The flexible-tip catheter was associated with enhanced cooling of catheter-tissue interface (31.1 ± 3.3°C vs 36.3 ± 3.7°C, P = 0.0001) in both perpendicular and nonperpendicular catheter orientations. This allowed more energy delivery (37.3 ± 8.9 W vs 33.7 ± 8.1 W, P = 0.004) to targeted tissue and resulted in larger lesions (median 194.7 [interquartile range: 113.1-333.8] mm(3) vs 170.9 [88.7-261.6] mm(3) , P = 0.03) than the rigid-tip catheter with larger maximum diameter (11.1 ± 2.6 mm vs 10.3 ± 2.1 mm, P = 0.03) and larger diameter at tissue surface (10.3 ± 2.4 mm vs 9.6 ± 1.7 mm, P = 0.01). Catheter orientation during ablation affected the efficiency of rigid-tip but not the flexible-tip catheter. The use of the flexible-tip catheter was associated with significantly less char formation on tissue (none vs 5.1% with rigid tip, P = 0.009). CONCLUSION: The Cool Flex™ catheter performed better than a rigid-tip catheter with enhanced cooling, larger ablation lesions, and no charring of targeted tissue.

Cardiac effects of electrical stun guns: does position of barbs contact make a difference?

BACKGROUND: The use of electrical stun guns has been rising among law enforcement authorities for subduing violent subjects. Multiple reports have raised concerns over their safety. The cardiovascular safety profile of these devices in relationship to the position of delivery on the torso has not been well studied. METHODS: We tested 13 adult pigs using a custom device built to deliver neuromuscular incapacitating (NMI) discharge of increasing intensity that matched the waveform of a commercially available stun gun (TASER(R) X-26, TASER International, Scottsdale, AZ, USA). Discharges with increasing multiples of output capacitances were applied in a step-up and step-down fashion, using two-tethered barbs at five locations: (1) Sternal notch to cardiac apex (position-1), (2) sternal notch to supraumbilical area (position-2), (3) sternal notch to infraumbilical area (position-3), (4) side to side on the chest (position-4), and (5) upper to lower mid-posterior torso (position-5). Endpoints included determination of maximum safe multiple (MaxSM), ventricular fibrillation threshold (VFT), and minimum ventricular fibrillation induction multiple (MinVFIM). RESULTS: Standard TASER discharges repeated three times did not cause ventricular fibrillation (VF) at any of the five locations. When the barbs were applied in the axis of the heart (position-1), MaxSM and MinVFIM were significantly lower than when applied away from the heart, on the dorsum (position-5) (4.31 +/- 1.11 vs 40.77 +/- 9.54, P< 0.001 and 8.31 +/- 2.69 vs 50.77 +/- 9.54, P< 0.001, respectively). The values of these endpoints at position-2, position-3, and position-4 were progressively higher and ranged in between those of position-1 and position-5. Presence of ventricular capture at a 2:1 ratio to the delivered TASER impulses correlated with induction of VF. No significant metabolic changes were seen after standard NMI TASER discharge. There was no evidence of myocardial damage based on serum cardiac markers, electrocardiography, echocardiography, and histopathologic findings confirming the absence of significant cardiac effects. CONCLUSIONS: Standard TASER discharges did not cause VF at any of the positions. Induction of VF at higher output multiples appear to be sensitive to electrode distance from the heart, giving highest ventricular fibrillation safety margin when the electrodes are placed on the dorsum. Rapid ventricular capture appears to be a likely mechanism of VF induction by higher output TASER discharges.

Do electrical stun guns (TASER-X26) affect the functional integrity of implantable pacemakers and defibrillators?

AIMS: High voltage electric current can adversely affect pacemakers (PM) and implantable cardioverter-defibrillator (ICD). The standard shock from an electrical stun gun (TASER- X26, TASER International, Scottsdale, AZ) consists of a 5-s long application of high voltage, low current pulses at 19 pulses per second. Its effect on the functional integrity of PM and ICDs is unknown. METHODS AND RESULTS: We tested the functional integrity of nine PMs and seven ICDs in a swine model after a standard stun gun shock. A transvenous, dual coil, bi-polar ICD lead (St Jude-SP01) and a PM lead were placed in the right ventricular (RV) apex and connected to pulse generators buried in the pre-pectoral pocket. The two darts were placed at the sternal notch (SN) and apex of the heart bracketing the device pocket. Standard neuromuscular incapacitating (NMI) discharges were delivered. Functional parameters of the devices and leads were checked before and after the shocks. The mean pacing thresholds, sensing thresholds, pacing impedances, and defibrillation coil impedances of the ICD lead were similar before and after the shocks. Similarly, pacing thresholds, sensing thresholds, and impedances of the PM lead were not significantly different before and after the shocks. No significant change was noted in battery voltage and projected longevity. Implantable cardioverter-defibrillator generators detected the NMI impulses at a mean cycle length of 176 +/- 20 ms with detection to charge time of 5.9 +/- 1.5 s. Shock delivery was aborted in all tests as tachycardia detection abruptly terminated at the end of the 5 s NMI application. None of the devices exhibited power on reset (POR), elective replacement indicator (ERI), or noise mode behaviour after the shock. CONCLUSION: Pacemakers and ICD generators and leads functions were not affected by the tested standard 5 s stun gun shocks.

Effects of cocaine intoxication on the threshold for stun gun induction of ventricular fibrillation.

OBJECTIVES: This study sought to assess cocaine's effects on Taser-induced ventricular fibrillation (VF) threshold in a pig model. BACKGROUND: Stun guns are increasingly used by law enforcement officials to restrain violent subjects, who are frequently intoxicated with cocaine and other drugs of abuse. The interaction of cocaine and the stun gun on VF induction is unknown. METHODS: We tested five adult pigs using a custom device built to deliver multiples of standard neuromuscular incapacitating (NMI) discharge that matched the waveform of a commercially available electrical stun gun (Taser X-26, Taser International, Scottsdale, Arizona). The NMI discharges were applied in a step-up and step-down fashion at 5 body locations. End points included determination of maximum safe multiple, minimum VF-inducing multiple, and ventricular fibrillation threshold (VFT) before and after cocaine infusion. RESULTS: Standard NMI discharges (x1) did not cause VF at any of the 5 locations before or after cocaine infusion. The maximum safe multiple, minimum VF-inducing multiple, and VFT of NMI application increased with increasing electrode distance from the heart. There was a 1.5- to 2-fold increase in these values at each position after cocaine infusion, suggesting decreased cardiac vulnerability for VF. Cocaine increased the required strength of NMI discharge that caused 2:1 or 3:1 ventricular capture ratios at all of the positions. No significant changes in creatine kinase-MB and troponin-I were seen. CONCLUSIONS: Cocaine increased the VFT of NMI discharges at all dart locations tested and reduced cardiac vulnerability to VF. The application of cocaine increased the safety margin by 50% to 100% above the baseline safety margin.

Coupled pacing improves cardiac efficiency during acute atrial fibrillation with or without cardiac dysfunction.

Coupled pacing (CP), a method for controlling ventricular rate during atrial fibrillation (AF), consists of a single electrical stimulation applied to the ventricles after each spontaneous activation. CP results in a mechanical contraction rate approximately one-half the rate during AF. Paired stimulation in which two electrical stimuli are delivered to the ventricles has also been proposed as a therapy for heart failure. Although paired stimulation enhances contractility, it greatly increases energy consumption. The primary hypothesis of the present study is that CP improves cardiac function during acute AF without a similar increase in energy consumption because of the reduced rate of ventricular contractions. In a canine model, CP was applied during four stages: sinus rhythm (SR), acute AF, cardiac dysfunction (CD), and AF in the presence of cardiac dysfunction. The rate of ventricular contraction decreased in all four stages as the result of CP. In addition, we determined the changes in external cardiac work, myocardial oxygen consumption, and myocardial efficiency in the each of four stages. CP partially reversed the effects of AF and CD on external cardiac work, whereas myocardial oxygen consumption increased only moderately. In all stages but SR, CP increased myocardial efficiency because of the marked increases in cardiac work compared with the moderate increases in total energy consumed. Thus this pacing therapy may be a viable therapy for patients with concurrent atrial fibrillation and heart failure.