Correlation of intracardiac electrogram with surface electrocardiogram in Brugada syndrome patients

The objective of this study was to correlate the electrocardiogram (ECG) modification during an Ajmaline challenge in patients affected by the Brugada syndrome and implanted with an implantable cardioverter-defibrillator (ICD) with the morphological changes of their ICD's intracardiac electrogram (IEGM).

Sixteen type 1 Brugada syndrome patients implanted with a St Jude Medical AnalyST(®) ICD were enrolled and underwent ajmaline challenge. Intracardiac electrograms and 12 lead ECG signals were collected over the duration of the study and analysed off-line. The right precordial ECG leads were in both the third and fourth intercostal space by putting V5 and V6 in V1 and V2 at the third intercostal space. Two patients were excluded from the analysis due to signal noise issues. Of the remaining 14 patients, 12 and 2 patients were adjudicated to have positive and negative ajmaline challenges, respectively, based on standard ECG criteria. In the ajmaline positive patients, the IEGM T wave amplitude changes were more prominent than those of the IEGM ST segment (-898 ± 463 vs. -55 ± 381 µV, P < 0.05). Furthermore, all of these T wave amplitude changes were in the negative polarity, whereas the change in polarity of the ST segment was mixed. The changes in the IEGM T wave amplitude and ST segment were significantly smaller in the ajmaline negative patients compared with those in the ajmaline positive patients [211 ± 158 (P < 0.05) and 107 ± 54 (P < 0.05) µV, respectively). Over all 14 analysable patients, the change in the ECG ST segment over the timecourse of the ajmaline challenge correlated better with the IEGM T wave amplitude change (R = 0.72 ± 0.33) than the IEGM ST segment change (R = 0.63 ± 0.33). Applying an IEGM T wave amplitude change cut-off of 400 µV for predicting the outcome of the ajmaline challenge yielded 92% sensitivity (11/12) and 100% specificity (2/2).

In Brugada patients, ajmaline challenge elicits significant T wave amplitude changes within the ICD IEGM, greater than those of the IEGM ST segment. This study is the first step to provide new tools able to continuously monitor the type I Brugada aspect in patients affected by the Brugada syndrome.