Potential proarrhythmic effects of implantable cardioverter-defibrillators

Electrical Stun Gun and Modern Implantable Cardiac Stimulators

The aim of the study is to investigate systematically the possible interactions between two types of stun guns and last-generation pacemakers and implantable defibrillators. Experimental measurements were performed on pacemakers and implantable defibrillators from five leading manufacturers, considering the effect of stun gun dart positioning, sensing modality, stun gun shock duration, and defibrillation energy level. More than 300 measurements were collected. No damage or permanent malfunction was observed in either pacemakers or implantable defibrillators. During the stun gun shock, most of the pacemakers entered into the noise reversion mode. However, complete inhibition of the pacing activity was also observed in some of the pacemakers and in all the implantable defibrillators. In implantable defibrillators, standard stun gun shock (duration 5 s) caused the detection of a shockable rhythm and the start of a charging cycle. Prolonged stun gun shocks (10-15 s) triggered the inappropriate delivery of defibrillation therapy in all the implantable defibrillators tested. Also in this case, no damage or permanent malfunction was observed. For pacemakers, in most cases, the stun guns caused them either to switch to the noise reversion mode or to exhibit partial or total pacing inhibition. For implantable defibrillators, in all cases, the stun guns triggered a ventricular fibrillation event detection. No risks resulted when the stun gun was used by a person wearing a pacemaker or an implantable defibrillator. This work provides novel and up-to-date evidence useful for the evaluation of risks to pacemaker/implantable defibrillator wearers due to stun guns.

Polymorphic ventricular tachycardia in the coronary care unit

OBJECTIVE

To describe the clinical experience of patients with polymorphic ventricular tachycardia (PMVT) in a hospital setting.

METHODS

A 2-year prospective, observational study of patients with symptomatic and asymptomatic PMVT admitted to the coronary care unit of a community medical center. Electrocardiograms were reviewed for a pattern diagnostic of PMVT, and the QTc interval of the baseline ECG was determined. Etiologic factors, management, and clinical outcomes were also analyzed.

RESULTS

The study included 27 patients (13 men) with a mean age of 66.6 +/- 10 years. Fourteen patients had a prolonged QTc interval >or=520 ms (group A), and 10 patients had a normal QTc interval <or=440 ms (group B). Acute hypokalemia (n = 7) in the setting of underlying heart disease was the principal cause of the acquired QT syndrome; other causally related factors included severe bradycardia and the proarrhythmic effect of drugs. Acute myocardial infarction (n = 6) was the principal cause of PMVT associated with a normal QTc interval; other causal factors included right ventricular cardiomyopathy and the proarrhythmic effect of electrical cardioversion. Eight patients (group C) had brief runs of asymptomatic nonsustained PMVT, which recurred in 5 patients as symptomatic sustained PMVT despite appropriate treatment. Cardiac arrest (63%) requiring emergency defibrillation was the predominant clinical presentation irrespective of the QT interval. Four patients (15%) died, but only 2 owing to refractory PMVT/VF.

CONCLUSION

PMVT with or without QTc prolongation is a sporadic tachyarrhythmia that has frequent malignant potential for cardiac arrest. Successful management mandates emergency defibrillation for cardiac arrest and other appropriate measures for suppression of PMVT. The prognosis of PMVT is improved when the cause is correctly identified and promptly treated.

Morphology discriminator feature for enhanced ventricular tachycardia discrimination in implantable cardioverter defibrillators

The morphology discriminator (MD) feature is an electrogram template matching algorithm that intends to improve tachycardia discrimination in implantable cardioverter defibrillators (ICDs). The aim of this study was to evaluate the performance of this feature during spontaneously occurring ventricular and supraventricular tachyarrhythmias and exercise induced sinus tachycardia. Twenty-three patients (20 men, 3 women; mean age 54.3 +/- 13.8 years) with pectorally implanted Ventritex Contour MD, Angstrom MD, and Profile MD ICDs were studied. The stability of the acquired morphology template and performance of the algorithm during spontaneous tachyarrhythmias were evaluated at follow-up. A treadmill exercise test was performed in 16 patients along with continuous telemetric monitoring of matching scores. A satisfactory template could be acquired at baseline in 22 (96%) patients. Variations in electrogram morphology necessitated new template acquisition in seven (30%) patients at first follow-up (6-8 weeks postimplant). During a mean follow-up of 9.1 +/- 3.7 months, 56 ventricular tachycardia (VT) and 15 supraventricular tachycardia episodes (sinus tachycardia in two-thirds) in 11 patients were all appropriately discriminated by the MD feature. Exercise testing showed appropriate discrimination of sinus tachycardia in 15 (94%) of 16 patients. A common observation was postshock changes in electrogram morphology that resulted in transient mismatch with the template. In conclusion, the recently introduced MD feature in ICDs has a high sensitivity for detection of VT and high specificity for rejection of sinus tachycardia. Postshock changes in electrogram morphology have been observed that may cause inappropriate redetection. Marked variations of electrogram morphology over time may be a concern in some patients, especially during lead maturation.