QT Prolongation During AV-Block and Development of Heart Failure

Background: Bradycardia leads to prolongation of the action potential and the QT interval. Some patients with atrio-ventricular (AV) block display excessive prolongation of the QT interval that cannot be explained by the bradycardia alone. This excessive prolongation of the action potential results from downregulation of potasium channels during the cardiac remodeling triggered by the bradycardia. We hypothesized that this may represent a compensatory phenomenon “intended” for recruitment of calcium ions to augment myocardial contractility to increase cardiac output when heartrate acceleration is impaired.

Objective: To assess the relation between the degree of QT prolongation, the levels of brain natriuretic peptide (BNP) and the degree of heart failure during AV-block.

Methods: We prospectively enrolled 105 consecutive patients presenting with high degree AV-block between 01/2016 and 12/2018. Clinical data were collected along with serial ECGs and serum BNP levels. Data were collected repeatedly until pacemaker implantation or initiation of isopreternol infusion.

Results: There was a significant correlation between BNP levels and the QT interval (r=0.3, p=0.006). On consecutive measurements (while awaiting pacemaker implantation), both the QT-interval and the BNP levels increased. Patients with symptoms duration of >3 days had longer QTc and higher BNP levels compared to those with shorter duration of symptoms (483 ms vs. 426 ms, p

Conclusion: BNP levels correlate with QT duration in patients with AV block, especially among patients with more acute presentation. Longer duration of symptoms may allow for a more gradual increase of the QT interval and BNP levels, albeit with possibly less overt heart failure.