Efficacy of low-energy T wave shocks for induction of ventricular fibrillation in patients with implantable cardioverter defibrillators.

The efficacy of low-energy T wave shocks for induction of ventricular fibrillation (VF) was evaluated in 33 patients undergoing implantable cardioverter defibrillator (ICD) implantation (33 sessions) or predischarge ICD testing (20 sessions). To induce VF, the ventricle was paced for eight cycles at a 400-ms cycle length (S1-S1), and the T wave was scanned with a monophasic shock (S2) delivered via the defibrillating lead system. Of 294 attempts, the T wave shocks induced VF in 65%, nonsustained ventricular tachycardia in 10%, and less than five ventricular beats in 25%. As compared with the failed T shocks, the mean energy of successful T wave shocks was higher and the S1-S2 coupling interval was shorter. When the S2 timing was examined in relation to the T wave peak, the VF induction efficacy was 37% for shocks delivered more than 70 ms before the T wave peak, 82% for shocks delivered 30-70 ms before the T wave peak, and 50% for shocks delivered less than 30 ms before or just after the T wave peak (P < .001). Thus, in patients undergoing ICD implantation or ICD conversion testing, the use of low-energy T wave shocks is an effective and safe method to provoke VF.

Implantable cardioverter-defibrillator advances.

Significant advances in the basic science of implantable cardioverter-defibrillator therapy have led to improvements in defibrillation waveforms and in capacitor technology. Nonthoracotomy devices with biphasic waveforms can be implanted with a near 100% success rate. Although fewer patients with implantable cardioverter-defibrillators are being treated with concomitant antiarrhythmic drug therapy, sotalol appears to decrease the defibrillation threshold. Controversy still exists over the optimal design for defibrillator sensing leads. Tachyarrhythmia detection enhancement increase specificity for sensing ventricular tachycardia but may risk undersensing. A variety of subsets of patients receiving implantable cardioverter-defibrillators have been identified; patients presenting with ventricular fibrillation appear to have the most unfavorable prognosis. Controversy exists as to the true impact of implantable cardioverter-defibrillator therapy on subsequent survival. Randomized clinical trials such as AVID (Antiarrhythmics Versus Implantable Defibrillators) are designed to determine the true benefits of implantable cardioverter-defibrillators and may lead to expanded indications.

Intravascular ultrasound imaging of an acute dissecting aortic aneurysm: a case report.

A case of acute dissecting aortic aneurysm is described in which intravascular ultrasonography was used at the time of aortography to produce real-time, 360 degree cross-sectional images of the aorta. The transmural vessel morphology visualized by this new catheter-based technology allowed confirmation of the diagnosis and identification of distal extension to the aortic bifurcation. The case demonstrates the unique potential of this modality in diagnosis and possible therapy in vascular diseases.