Sodium channel-blocking agents are routinely used to unveil the Brugada syndrome in patients in whom the typical electrocardiographic pattern is absent or doubtful. In this article, the authors report a patient with syncopal episodes of unknown origin in whom the conventional electrocardiographic result was normal and a negligibly small "saddle back" type repolarization was present in lead V2 recorded 2 intercostal spaces above the conventional site. Intravenous ajmaline (50 mg) did not elicit the type 1 pattern of the Brugada syndrome in the precordial leads obtained at their usual level, but a clear-cut coved-type repolarization was apparent in high right precordial leads. These findings indicate that high precordial leads should be routinely recorded while assessing the ajmaline test in patients suspected of having the Brugada syndrome.

The anterograde refractory period (RP) of the accessory pathway (AP) is the main determinant factor of ventricular rate during atrial fibrillation in the Wolff-Parkinson-White (WPW) syndrome. We describe 3 examples of anterograde supernormal conduction (SNC) and 1 of retrograde SNC in APs. The paradoxical early recovery of propagation due to SNC, well inside a prolonged anterograde RP in the AP, may play a relevant role to determine the rate of ventricular response during atrial fibrillation, eventually leading to extremely fast ventricular rates, syncope, and even ventricular fibrillation in patients with WPW syndrome supposed a priori to be exposed to a low risk of sudden cardiac death. This may require very precise conditions, including an enhanced adrenergic influence on the heart. Retrograde SNC in APs may also participate in the mechanism of paroxysmal supraventricular tachycardias that are not easily induced by programmed cardiac stimulation.

Key Clinical MessageInverted connection of the atrial and ventricular leads is an unusual circumstance during the implantation of a dual‐chamber pacemaker. Yet, PMT may present in the absence of complex mechanisms. The detection and termination algorithms used by the device proved to be efficient for the adequate diagnosis and treatment.