Mexiletine Prevents Recurrent Torsades de Pointes in Acquired Long QT Syndrome Refractory to Conventional Measures

The purpose of this study was to examine the role of mexiletine, a late sodium current (I_Na-L) blocker, in acute termination of torsades de pointes (TdP) refractory to conventional therapy in acquired long QT syndromes (LQTS).

Long QT interval can predispose to TdP and is therefore associated with significant mortality. Currently, there is no available pharmacotherapy to target directly the ionic basis of most LQTS for the acute termination of TdP. Earlier evidence highlighted the role of I_Na-L in the pathophysiology of long QT and TdP, particularly in patients with congenital LQTS.

Twelve patients with TdP caused by acquired LQTS were treated with mexiletine after failure of conventional treatment including discontinuation of QT-prolonging drugs, intravenous administration of magnesium, and correction of serum electrolyte abnormalities.

No recurrence of TdP occurred within 2 h after initiation of treatment with mexiletine in all 12 patients. Macro T-wave alternans accompanied by QT prolongation, an electrocardiographic precursor of TdP that was seen in 3 patients, was also abolished by mexiletine. Treatment with mexiletine shortened the QTc interval from 599 ± 27 ms to 514 ± 16 ms (p = 0.001). The interval from the peak to the end of the T-wave (T_p-e interval) decreased from 145 ± 18 ms to 106 ± 9 ms (p = 0.005). The T_p-e/QT ratio decreased from 0.27 ± 0.02 to 0.23 ± 0.018 (p = 0.01). Mexiletine had no significant effect on QRS complex duration.

I_Na-L blockade with mexiletine may be an effective treatment approach to terminate refractory TdP from several acquired causes of LQTS.