Showing papers by "Gan-Xin Yan published in 2009"

Is there a significant transmural gradient in repolarization time in the intact heart? Cellular basis of the T wave: a century of controversy.

Abstract: The ECG is one of the oldest and most versatile noninvasive cardiac diagnostic tests. It has remained in use essentially in its original form despite dramatic advances in cardiac electrophysiology. In May 1887, Augustus Desire Waller recorded the first human Electrogram using a primitive instrument called a Libbmann capillary electrometer. It had 2 deflections corresponding to ventricular depolarization and repolarization.1 In 1903, Willem Einthoven invented the String Galvanometer—a more sophisticated voltage recording instrument and recorded an Elektrokardiogramm with 5 deflections that he named PQRST.2 Response by Opthof et al p 80 Since its initial invention, the body surface ECG has become a commonly used and extremely valuable test for the diagnosis of a variety of cardiac conditions. Despite a century of prolific use and intensive investigation, the cellular basis of ECG waveforms, particularly the T wave, remains a matter of debate. The saga of the T wave began in 1856, when 2 German physiologists Kolliker and Muller attempted to explore the electric activity of the heart using frog sciatic nerve attached to gastroenemius muscle as a voltage recording instrument and observed 2 contractions (see review by Noble and Cohen3). In retrospect, the second “contraction” probably reflected a voltage gradient related to the T wave of Einthoven. In 1883, Burdon-Sanderson and Page4 were the first to demonstrate that in the frog’s heart, the wave of excitation spreads from the base to the apex of the ventricle. The record was diphasic, with the first positive (R) wave followed by a negative (T) wave. They also demonstrated that the T wave corresponds to repolarization of the ventricle. Similar series of experiments by Bayliss and Starling in 18925 in the canine heart showed that the T waves are usually upright in mammals. This was followed by Mines6 on …

Pharmacotherapy of cardiac arrhythmias--basic science for clinicians.

Abstract: Cardiac arrhythmias occur in approximately 5.3% of the population and contribute substantially to morbidity and mortality. Pharmacological therapy still remains the major approach in management of patients with nearly every form of cardiac arrhythmia. Effective and safe management of cardiac arrhythmias with antiarrhythmic drugs requires understanding of basic mechanisms for various cardiac arrhythmias, clinical diagnosis of an arrhythmia and identification of underlying cardiac diseases, pharmacokinetics, and antiarrhythmic properties of each individual antiarrhythmic drug. Most cardiac arrhythmias occur via one of the two mechanisms: abnormal impulse formation and reentry or both. Antiarrhythmic drugs primarily work via influencing cardiac automaticity or triggered activity or by their effects on effective refractoriness of cardiac cells. Proarrhythmic effects of antiarrhythmic drugs are also briefly discussed in this review article.

Should catheter ablation be the preferred therapy for reducing ICD shocks?: Ventricular tachycardia ablation versus drugs for preventing ICD shocks: role of adjuvant antiarrhythmic drug therapy.

Abstract: In 1980, Mirowski et al1 implanted the first implantable cardioverter-defibrillator (ICD) in a young female with recurrent ventricular fibrillation and provided an innovative approach to aborted sudden cardiac death (SCD). Although the ICD was considered a treatment of last resort during that incipient stage, subsequent years have witnessed prolific expansion of indications for ICD implantation.2 Several large-scale clinical trials have demonstrated its efficacy for both primary and secondary prevention of SCD in patients with ischemic and nonischemic cardiomyopathy.3,4 ICD therapy in such high-risk patients has been shown to improve survival compared with conventional antiarrhythmic drug therapy alone.3,4 The number of ICD implantations has increased significantly in the last decade, with a concurrent decrease in the use of stand-alone antiarrhythmic drugs for ventricular indications.5–7 Current ICDs have sophisticated programming capabilities, atrial and bipolar leads, and are able to deliver antitachycardia pacing algorithms (ATP) in addition to defibrillating shocks. Response by Kuck on p 705 Typically, patients who receive ICDs are at high risk for recurrent arrhythmia; hence, most patients receive 1 or more ICD therapies for spontaneous arrhythmias after implantation.3 Despite the technological evolution of ICD systems, more than 20% of shocks are due to supraventricular arrhythmia and hence are inappropriate.8–10 The ICD uses ATP or defibrillating shocks to terminate episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF). Although the ICD aborts VT/VF, many patients continue to have symptoms such as dizziness, palpitations, nervousness, flushing, or syncope before receiving an ICD shock.11 When the shock is finally delivered, it is physically and emotionally painful and so noxious that 23% of patients dread shocks and 5% of patients prefer to do without an ICD and “take their chances.”12 A significant prevalence of sadness, depression, and even anxiety disorders have been reported after …