Pr Interval on Resting Ecg in Patients With Mobitz-1 Second-Degree Atrioventricular Block Detected on Ambulatory Ecg Monitoring

Prolonged PR interval is traditionally regarded as an electrocardiographic marker of delayed atrioventricular conduction and is known to predict future episodes of second- and third-degree atrioventricular block. Nevertheless, clinically significant episodes of second- and third-degree atrioventricular block may also occur in individuals with a normal PR interval on a standard resting electrocardiogram (ECG), indicating that normal baseline atrioventricular conduction does not exclude intermittent conduction abnormalities. Although Mobitz-1 second-degree atrioventricular block has long been considered a relatively benign rhythm disturbance, recent evidence has challenged this concept. A contemporary study demonstrated that the presence of Mobitz-1 atrioventricular block was associated with a 2.3-fold increase in the rate of cardiovascular death, suggesting that this conduction disorder may have greater clinical significance than previously believed. Current clinical guidelines recommend permanent pacemaker implantation for patients with Mobitz-2 second-degree atrioventricular block, infranodal 2:1 atrioventricular block, high-degree atrioventricular block, and third-degree atrioventricular block regardless of symptom status because of the substantial risk of progression to complete heart block. In contrast, permanent pacing in patients with Mobitz-1 second-degree atrioventricular block is generally indicated for those with symptoms attributable to bradycardia or for patients in whom electrophysiological evaluation demonstrates an intra-Hisian or infra-Hisian site of conduction delay. The study aimed to evaluate the relationship between the PR interval measured on a resting ECG and the occurrence of Mobitz-1 second-degree atrioventricular block detected by ambulatory ECG monitoring. Recordings from ambulatory ECG monitoring and corresponding resting ECGs of 40 patients with documented Mobitz-1 second-degree atrioventricular block were retrospectively analyzed. The median maximal PR interval recorded during ambulatory monitoring was 245.0 [212.5–305.0] ms, while the median maximal RR interval was 2038.0 [1819.0–2356.0] ms. On resting ECG, the median PR interval was 205.0 [167.5–245.0] ms. A prolonged PR interval (≥200 ms) on resting ECG was identified in 22 patients (55.0 %). Among these individuals, only 7 (17.5 %) patients had mild PR interval prolongation ranging from 200 to 220 ms, whereas the remaining patients exhibited more pronounced prolongation. Importantly, a normal PR interval (<200 ms) on resting ECG was observed in 18 patients (45.0 %) despite documented episodes of Mobitz-1 second-degree atrioventricular block during ambulatory ECG monitoring. There was a strong positive correlation was found between the PR interval measured on resting ECG and the maximal PR interval recorded during ambulatory monitoring (r = 0.76, p < 0.01). These findings demonstrate that nearly half of patients with Mobitz-1 second-degree atrioventricular block documented by ambulatory ECG monitoring have a normal PR interval on resting ECG. Consequently, the PR interval measured on a resting ECG should not be considered a reliable marker for excluding episodic Mobitz-1 second-degree atrioventricular block. Ambulatory ECG monitoring remains an essential diagnostic tool for detecting intermittent atrioventricular conduction disturbances that may not be apparent during routine resting ECG.