Abstract
Patients with Brugada syndrome (BrS) can show a leftward deviation of the frontal QRS-axis upon provocation with sodium channel blockers. The cause of this axis change is unclear. In this study, we aimed to determine (1) the prevalence of this left axis deviation and (2) to evaluate its cause, using the insights that could be derived from vectorcardiograms. Hence, from a large cohort of patients who underwent ajmaline provocation testing (n = 1430), we selected patients in whom a type-1 BrS-ECG was evoked (n = 345). Depolarization and repolarization parameters were analyzed for reconstructed vectorcardiograms and were compared between patients with and without a >30° leftward axis shift. We found (1) that the prevalence of a left axis deviation during provocation testing was 18% and (2) that this left axis deviation was not explained by terminal conduction slowing in the right ventricular outflow tract (4th QRS-loop quartile: +17 ± 14 ms versus +13 ± 15 ms, nonsignificant) but was associated with a more proximal conduction slowing (1st QRS-loop quartile: +12[8;18] ms versus +8[4;12] ms, p < 0.001 and 3rd QRS-loop quartile: +12 ± 10 ms versus +5 ± 7 ms, p < 0.001). There was no important heterogeneity of the action potential morphology (no difference in the ventricular gradient), but a left axis deviation did result in a discordant repolarization (spatial QRS-T angle: 122[59;147]° versus 44[25;91]°, p < 0.001). Thus, although the development of the type-1 BrS-ECG is characterized by a terminal conduction delay in the right ventricle, BrS-patients with a left axis deviation upon sodium channel blocker provocation have an additional proximal conduction slowing, which is associated with a subsequent discordant repolarization. Whether this has implications for risk stratification is still undetermined.
Highlights
In patients suspected of Brugada syndrome (BrS), documenting the spontaneous type-1 BrS-ECG or, after, provocation testing with a cardiac sodium channel blocker is a required criterion for the BrS-diagnosis [1]
We evaluated vectorcardiograms of a large cohort of patients suspected of BrS who underwent provocation testing in order to (1) determine the prevalence of a left axis deviation in patients with a positive ajmaline test result and (2) to evaluate the cause of this left axis deviation
We show that (1) the prevalence of a left axis deviation during ajmaline provocation testing in patients with a positive ajmaline test is 17.5% and (2) that this left axis deviation is not caused by conduction slowing in the right ventricular outflow tract (RVOT) but is due to additional conduction slowing in the more proximal conduction system
Summary
In patients suspected of Brugada syndrome (BrS), documenting the spontaneous type-1 BrS-ECG or, after, provocation testing with a cardiac sodium channel blocker is a required criterion for the BrS-diagnosis [1]. As the right ventricular outflow tract (RVOT) is a critical area in the development of the type-1 BrS-ECG and its associated malignant arrhythmias [1,4], this left axis deviation may be caused, among others, by exaggerated conduction slowing in the RVOT exceeding the conduction slowing that is already associated with the development of the type-1 ECG [1,4,5] This could result in a diminished rightward vector and a more pronounced and leftward vector, resulting in a leftward axis deviation [1]. When the underlying pathophysiological mechanisms underlying the ECG variations in BrS are unraveled, this could contribute to risk stratification
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
