Introduction
The PR interval measured from the surface electrocardiogram (ECG) is
considered an indicator reflecting atrial and atrioventricular node
myocyte depolarization and conduction1. PR
prolongation, usually defined as PR interval >200ms, is a
relatively common electrocardiographic finding with prevalence of 2-6%
in general population2–4. However, the prognosis
value of PR prolongation is controversial due to the many factors that
can influence the PR interval5. Previous studies have
demonstrated that PR prolongation is associated with the occurrence of
atrial fibrillation and left ventricle
dysfunction6–8. The prolonged PR interval is also
related to an increased risk of death in patients with cardiovascular
disease (CVD) including heart failure (HF), coronary artery disease
(CAD) and hypertrophic cardiomyopathy (HCM)9–11.
Since this correlation is less striking in the general population,
abnormal PR interval is less well appreciated especially in the
population free of CVD2,12,13.
The P-wave duration is a crucial component of the PR interval, and the
link between P-wave duration
prolongation and adverse outcomes, including increased risk of atrial
arrhythmias and mortality, is well established14.
Soliman et al using the data from the Third National Health and
Nutrition Examination Survey (NHANES III) suggested that the prognostic
significance associated with PR prolongation is largely determined by
P-wave duration15. Meanwhile, since specific
information on the P-wave has been rarely reported in the studies
addressing PR prolongation, this opinion makes the clinical utility of
PR interval be questioned. But there is no denying that hemodynamic
abnormalities were indeed identified in this population with PR
prolongation. In case of PR
prolongation, atrial systole occurs
much earlier than the onset of left ventricular (LV) systole, resulting
in the impaired effective LV diastolic filling time16.
Another important implication of PR prolongation on hemodynamics is
diastolic mitral regurgitation. Increased mitral regurgitation,
decreased LV compliance as well as impaired relaxation are inextricably
linked17–19.
Starting from these observations, we proposed that LV diastolic function
may be a significant factor for PR prolongation risk stratification.
Meanwhile, the QRS axis is an important ECG parameter to reflect LV
diastolic function20. We therefore designed this study
to identify those people with PR prolongation who have poor prognosis in
the population without CVD by using QRS axis.