Risk stratification in surgically repaired tetralogy of Fallot

Tetralogy of Fallot is the most common form of congenital heart disease in implantable cardioverter–defibrillator (ICD) recipients. Indeed, sudden death of presumed arrhythmic etiology is the most frequent mode of demise in patients with surgically repaired tetralogy of Fallot, often in early-to-mid adulthood. Nevertheless, the overall annual incidence of sudden death is actually low. Therein lies the major challenge of risk stratification. This review highlights some of the complexities involved in risk stratifying patients with tetralogy of Fallot, underscoring the importance of avoiding oversimplification by means of a rigid algorithm that dictates therapy. To complement sound clinical judgment, a quantitative probabilistic approach is presented, which considers the body of literature from primary prevention ICD trials, risk factors identified by observational studies, the value of programmed ventricular stimulation and insights gleaned from studying ICD recipients with tetralogy of Fallot.     

Implantable rhythm devices and electromagnetic interference: myth or reality?

Current medical guidelines have prompted implementation of increasing numbers of implantable rhythm devices, be they pacemakers, internal cardioverter–defibrillators or loop recorders. These devices rely on complex microcircuitry and use electromagnetic waves for communication. They are, therefore, susceptible to interference from surrounding electromagnetic radiation and magnetic energy. Hermetic shielding in metallic cases, filters, interference rejection circuits and bipolar sensing have contributed to their relative resistance to electromagnetic interference (EMI) in household and workplace environments. Device interactions have occurred in hospitals where EMI sources are ubiquitous, including radiation, electrocautery and MRI exposures. However, with rapidly evolving technology, devices and potential sources of EMI continue to change. This review provides a contemporary overview of the current state of knowledge regarding risks attributable to EMI; highlights current limitations of implantable rhythm devices; and attempts to distinguish myths from realities.     

Azimilide dihydrochloride

Azimilide dihydrochloride is an antiarrhythmic drug with Vaughn Williams class III properties, which blocks both fast (IK_r) and slow (IK_s) components of the delayed rectifier cardiac potassium channel. The drug slows the heart rate slightly and, like other class III antiarrhythmic drugs, prolongs ventricular repolarization and thus, the QT interval. Unlike sotalol, another class III antiarrhythmic drug, azimilide does not exhibit reverse-use dependence, that is, its binding characteristics and effectiveness are not related to the heart rate. Azimilide is 85% bioavailable, reaches peak blood concentrations in 6–8 h and has a long elimination half-life of 114 h. Clinical trials have utilized once-daily dosing. These trials have tested the use of the drug for patients with supraventricular and ventricular arrhythmias.     

Characterization and Management of Arrhythmic Events in Young Patients With Brugada Syndrome

Background

Information on young patients with Brugada syndrome (BrS) and arrhythmic events (AEs) is limited.

Recording of Pacing Stimulus Artifacts by Endovascular Defibrillation Lead Systems: Comparison of True and Integrated Bipolar Circuits

Background: The occurrence ICD undersensing of ventricular fibrillation due to the presence of a pacing stimulus artifact (PSA) is in part related to the amplitude of the artifact recorded on the ICD rate sensing circuit. There is little comparative data regarding PSA amplitude recorded by commercial ICD rate-sensing circuits.Purpose: To compare PSA amplitude recorded by commercial endovascular defibrillation leads utilizing integrated or true bipolar sensing circuits.Methods: Nineteen large (60–120 kg) pigs were utilized. Two different commercial endovascular defibrillation leads were evaluated, each with its distal tip located at the right ventricular apex: (1) Medtronic Transvene; and (2) CPI Endotak. Three different rate-sensing circuits were evaluated: (1) Transvene true bipolar (tip-ring); (2) Transvene integrated bipolar (tip-coil); and (3) Endotak integrated bipolar (tip-coil). Using a separate pacing lead located at the left ventricular apex (n = 19 animals) or right ventricular outflow tract (n = 10 animals), pacing was performed at a pulse width of 0.5 milliseconds at outputs of 1.5, 5 and 10 volts. PSA amplitude was recorded at each output by each circuit.Results: During pacing from the left ventricular apex, at each pacing output voltage the PSA amplitude recorded by the true bipolar circuit (0.6 ± 0.1 mV at 1.5 volts, 2.0 ± 0.5 mV at 5 volts, 3.7 ± 0.8 mV at 10 volts) was significantly smaller than recorded by the Transvene integrated circuit (1.4 ± 0.3 mV at 1.5 volts, 3.8 ± 0.7 mV at 5 volts, 4.1 ± 0.8 mV at 10 volts) or the Endotak integrated circuit (1.8 ± 0.4 mV at 1.5 volts, 4.2 ± 1.0 mV at 5 volts, 6.3 ± 1.8 mV at 10 volts). During pacing from the right ventricular outflow tract, at each pacing output voltage the PSA amplitude recorded by the true bipolar circuit (0.7 ± 0.1 mV at 1.5 volts, 1.7 ± 0.4 mV at 5 volts, 4.0 ± 0.7 mV at 10 volts) was significantly smaller than recorded by the Transvene integrated circuit (1.1 ± 0.4 mV at 1.5 volts, 3.9 ± 1.2 mV at 5 volts, 7.5 ± 1.8 mV at 10 volts) or the Endotak integrated circuit (1.6 ± 0.7 mV at 1.5 volts, 4.3 ± 1.7 mV at 5 volts, 7.5 ± 2.6 mV at 10 volts). For both pacing sites, the PSA amplitude recorded by the two integrated circuits was not significantly different.Conclusions: For a given pacing output voltage, PSA amplitude recorded by commercial endovascular rate sensing/defibrillation leads is greater when the sensing circuit is integrated than when it is true bipolar. These data may be helpful in planning ICD implantation in patients with previously implanted permanent pacemakers.