[Evaluation of the PR intervals in normal and prolonged maximum limit with short QRS]

Abstract

Purpose: Evaluation of the A-V node function by determining the Wenckebach period (WP) and atropine response in cases of normal PR interval, PR interval at maximum normal range and prolonged PR interval, all with short QRS.

Patients and methods: 129 patients, 79 male and 50 female, aged 17 to 84 years (mean 59), asymptomatic or with complaints of palpitations, dizziness, presyncope or syncope has been studied. ECG showed supra-ventricular tachycardia, first degree A-V block or intermittent Mobitz I type A-V block and sick sinus syndrome. Preexcitation (WPW) syndrome and longitudinal A-V dissociation were excluded. Electrical transoesophageal atrial stimulation was performed in all patients for evaluating the PR interval and WP. Atropine test was performed in a group of 16 patients. Based on the values of the WP, patients were divided into three groups: group I, WP greater than or equal to 125 ppm (N = 88); group II, WP ranging 125-110 ppm (N = 16) and group III, WP less than or equal to 110 ppm (N = 25).

Results: There was a good decreasing lineal correlation between the PR interval and the WP only in the group III (r = 0.76, p less than 0.01). PR interval greater than 240 ms had greatest and significant incidence in the group III in relation to the other groups in which the number of WP post-atropine normalization was observed.

Conclusion: There is a strong linear decreasing correlation between the PR interval of the ECG and the WP in individuals with WP less than or equal to 110 ppm. PR interval greatest than 0.24 ms corresponds better to WP below 110 ppm (mean 90 ppm) and the majority of these patients do not normalize the WP with the atropine. We suggest the term "first degree A-V block" for those cases with PR interval greater than 240 ms and "A-V depression" for the cases with PR interval shorter than 240 ms when recorded on the surface electrocardiogram and have been normalized with atropine.