The Long QT Syndrome and Torsade De Pointes

The LQTS is a prime example of how molecular biology, ion channel, cellular, and organ physiology, coupled with clinical observations, promise to be the future paradigm for advancement of medical knowledge. Both the congenital and acquired LQTS are due to abnormalities (intrinsic and/or acquired) of the ionic currents underlying cardiac repolarization. In this review, the continually unraveling molecular biology of congenital LQTS is discussed. The various pharmacological agents associated with the acquired LQTS are listed. Although it is difficult to predict which patients are at risk for TdP, careful assessment of the risk-benefit ratio is important before prescribing drugs known to be able to cause QT prolongation. The in vivo electrophysiological mechanism of TdP in the LQTS is described using, as a paradigm, the anthopleurin-A canine model, a surrogate for LQT3. In the LQTS, prolonged repolarization is associated with increased spatial dispersion of repolarization. Prolongation of repolarization also acts as a primary step for the generation of EADs. The focal EAD induced triggered beat(s) can infringe on the underlying substrate of inhomogeneous repolarization to initiate polymorphic reentrant VT, sometimes having the characteristic twisting QHS configuration known as TdP. The review concludes by discussion of the clinical manifestations and current management of both the congenital and acquired LQTS. The initial therapy of choice for the large majority of patients with the congenital LQTS is a beta-blocking drug. This therapy seems to be effective in LQT1 and LQT2 patients, but may not be as effective in LQT3 patients. Other therapeutic options include pacemakers, cervicothoracic sympathectomy, and the implantable cardioverter defibrillator. Recent molecular genetic studies have suggested several genotype specific therapies; however, long-term efficacy data are not available.     

His Bundle Extrasystoles Revisited: The Great Electrocardiographic Masquerader

A 74‐year‐old man with past history of near syncope presented with frequent periods of second‐degree atrioventricular block (2° AVB). An electrophysiological study revealed prolonged atrial‐His and His‐ventricular (HV) intervals and frequent His bundle (H) extrasystoles. The latter manifested in the surface electrocardiogram as premature atrial, junctional, or ventricular beats, as well as 2° AVB that mimicked Wenckebach or Mobitz II block. Procainamide markedly suppressed H extrasystole. However, because of the presence of prolonged HV interval and history of presyncope, a permanent pacemaker was inserted. The case illustrates the varied manifestation of H extrasystole and presents guidelines for management. (PACE 2011; e56–e59)     

Aminophylline: could it act as an antioxidant in vivo?

Abstract. Potential antioxidant properties of aminophylline and theophylline were investigated. We have found that these drugs, though ineffective against superoxide anion and hydrogen peroxide, are scavengers of hydroxyl radical (OH·). Indeed, second-order rate constants (k) of aminophylline and theophylline with OH· are about 1.9 times 10¹⁰ mol^-1 s^-1 and 4.5 times 10⁹ mol^-1 s^-1, respectively. Ethylenediamine, which is present in the aminophylline molecule, significantly contributes to this marked OH· scavenging activity, since it is characterized by a high k value, i.e. about 8 times 10⁹ mol^-1 s^-1. However, when using therapeutically relevant concentrations of the methylxanthines (9 and 13 μmL^-1), significant antioxidant effects against OH·-induced oxidant injury are evident only with aminophylline. Although all three substances can apparently bind and inactivate iron, only aminophylline is effective at 9 and 13 μgmL^-1; also this action is favoured by ethylenediamine. Moreover, therapeutic concentrations of aminophylline, but not of theophylline, are capable of antagonizing hypochlorous acid (HOC1); this effect is entirely due to the presence of ethylenediamine. Oxidant species, such as OH· and HOC1, have been implicated in the pathophysiology of asthma; it could be hypothesized, therefore, that some therapeutic effects of aminophylline may be related to its antioxidant properties, which are partly or totally attributable to ethylenediamine, depending on the chemical identity of the prooxidant antagonized (e.g. iron/OH· or HOC1). Aminophylline antioxidant capacity should be taken into account when investigating the lung epithelial lining fluid antioxidant capacity and oxidative stress indices in humans.     

Catheter Entrapment in the Mitral Valve Apparatus Requiring Surgical Removal: An Unusual Complication of Radiofrequency Ablation

We describe a patient with Wolff-Parkinson-White syndrome in whom a steerable catheter became entrapped in the mitral valve apparatus, during radiofrequency ablation. Treatment consisted of surgical removal of the catheter. The occurrence of this previously unreported complication stresses the need for on-going monitoring of risk and benefits of electrophysiological interventions.     

Captopril has no significant scavenging antioxidant activity in human plasma in vitro or in vivo

1 Captopril has been reported to possess hydroxyl radical (OH) and hypochlorous acid (HOCl) scavenging effects, which could contribute to its therapeutic activity in the clinical setting.
2 The objective of the present study was to determine whether therapeutically achievable captopril concentrations could augment antioxidant properties of human plasma and protect it against OH- and HOCl-driven oxidant injury in vitro . Possible drug influences on systemic oxidative stress status in vivo were also investigated in subjects taking 50  mg captopril orally by measuring plasma and red blood cell peroxidation, as well as plasma protein thiols.
3 The results show that captopril is incapable of enhancing antioxidant properties of human plasma, of protecting it against specific oxidative attack and of decreasing systemic oxidant load in vivo .
4 The present data, therefore, do not support the contention of a beneficial action of captopril through systemic antiradical-antioxidant effects in human beings.