The electromechanical window is no better than QT prolongation to assess risk of Torsade de Pointes in the complete atrioventricular block model in dogs

BACKGROUND AND PURPOSE

The electromechanical window (EMW), the interval between the end of the T-wave and the end of the left ventricular pressure (LVP) curve, has recently been proposed as a predictor of risk of Torsade de Pointes (TdP) in healthy animals, whereby a negative EMW (mechanical relaxation earlier than repolarization) after drug administration indicates an increased TdP risk. The aims of this study were to assess (i) the effect of the ventricular remodelling in the canine chronic, complete atrioventricular block (CAVB) model on EMW; (ii) the effect of the I(Kr) -blocker dofetilide on EMW; and (iii) the correlation of EMW with TdP inducibility.

EXPERIMENTAL APPROACH

Our 11 year database of experiments of CAVB in dogs under general anaesthesia was reviewed and experiments included if ECG and LVP were recorded simultaneously at spontaneous rhythm. In total, 89 experiments in 44 dogs were appropriate and were analysed.

KEY RESULTS

During normally conducted sinus rhythm or acute atrioventricular block, EMW was positive. During CAVB, EMW was decreased to negative values. Dofetilide further reduced EMW before inducing repetitive TdP in 82% of the experiments. However, subclassification into inducible and non-inducible dogs revealed no difference in EMW. Analysis of the components of EMW revealed that the observed changes in EMW were solely caused by QT prolongation.

CONCLUSIONS AND IMPLICATIONS

In the canine CAVB model, ventricular remodelling and I(Kr) block by dofetilide are associated with negative EMW values, but this reflects QT prolongation, and implies that the EMW lacks specificity to predict dofetilide-induced TdP.

Robust anti-arrhythmic efficacy of verapamil and flunarizine against dofetilide-induced TdP arrhythmias is based upon a shared and a different mode of action

BACKGROUND AND PURPOSE

The high predisposition to Torsade de Pointes (TdP) in dogs with chronic AV-block (CAVB) is well documented. The anti-arrhythmic efficacy and mode of action of Ca(2+) channel antagonists, flunarizine and verapamil against TdP were investigated.

EXPERIMENTAL APPROACH

Mongrel dogs with CAVB were selected based on the inducibility of TdP with dofetilide. The effects of flunarizine and verapamil were assessed after TdP and in different experiments to prevent dofetilide-induced TdP. Electrocardiogram and ventricular monophasic action potentials were recorded. Electrophysiological parameters and short-term variability of repolarization (STV) were determined. In vitro, flunarizine and verapamil were added to determine their effect on (i) dofetilide-induced early after depolarizations (EADs) in canine ventricular myocytes (VM); (ii) diastolic Ca(2+) sparks in RyR2(R4496+/+) mouse myocytes; and (iii) peak and late I(Na) in SCN5A-HEK 293 cells.

KEY RESULTS

Dofetilide increased STV prior to TdP and in VM prior to EADs. Both flunarizine and verapamil completely suppressed TdP and reversed STV to baseline values. Complete prevention of TdP was achieved with both drugs, accompanied by the prevention of an increase in STV. Suppression of EADs was confirmed after flunarizine. Only flunarizine blocked late I(Na). Ca(2+) sparks were reduced with verapamil.

CONCLUSIONS AND IMPLICATIONS

Robust anti-arrhythmic efficacy was seen with both Ca(2+) channel antagonists. Their divergent electrophysiological actions may be related to different additional effects of the two drugs.

Dealing with a positive result: routine HIV testing of pregnant women in Vietnam

HIV testing is an essential component of PMTCT. It can be offered to pregnant women through different testing models, ranging from voluntary counseling and testing (VCT) to routine and mandatory testing. This study was conducted in Hanoi, Vietnam, where HIV-prevalence is low among the general population, but high among young, urban, sexually active, male intravenous drug users. Women who want to deliver in a state hospital are routinely tested for HIV in the absence of well-defined opt-out procedures. In-depth interviews with a convenience sample of 38 seropositive pregnant women and mothers and 53 health workers explored the acceptability of routine testing. Patients and healthcare workers appeared to accept routine 'blood' tests (including HIV tests) because they feel uncomfortable discussing issues specific to HIV/AIDS. To avoid having to inform women directly about their HIV status, health workers at routine testing sites rely on the official notification system, shifting the responsibility from the hospitals to district and commune health staff. The notification system in Hanoi informs these local officials about the HIV status of people living in their catchment area without patients' consent. Our study shows that this non-confidential process can have serious social, economic and health consequences for the HIV-positive women and their children.