First-degree atrio-ventricular (AV) block is defined as a PR interval longer than 200 ms.
In some cases, loss of AV synchrony because of a marked prolongation of the PR interval may cause important haemodynamic alterations, with subsequent decrease in cardiac output and symptoms of heart failure, mimicking a pacemaker syndrome, so-called ‘pseudo-pacemaker syndrome’.
Pseudo-pacemaker syndrome is rare and is a Class IIa recommendation for a pacemaker implantation
Extremely prolonged PR interval (300-400 ms).
ECG 1 Pseudo-pacemaker symptoms in a patient with extremely prolonged PR interval
1) Patrice Carroz, Dominique Delay, Grégoire Girod, Pseudo-pacemaker syndrome in a young woman with first-degree atrio-ventricular block, EP Europace, Volume 12, Issue 4, April 2010, Pages 594–596, https://doi.org/10.1093/europace/eup373
2) Stanković I, Putniković B, Panić M, Vlahović-Stipac A, Nesković AN. [Pseudopacemaker syndrome and marked first-degree atrioventricular block: case report]. Srp Arh Celok Lek. 2010 Sep-Oct;138(9-10):635-8. Serbian. doi: 10.2298/sarh1010635s. PMID: 21180095.