The major findings of the current study were as follows: (1) MS patients exhibited a longer maximum P-wave and higher PWD as compared to the healthy individuals; (2) PWD and P-wave duration were strongly correlated with MS. (3) According to the ROC curve, it was found that the cut-off values for maximum P-wave duration and PWD for predicting the MS were 119.50 ms and 42.50 ms for PWD, respectively. These findings may effectively contribute to the early detection of MS, which in turn may help the clinicians to impede the rate of MS progression.
PWD was first defined in 1998 by Dilaveris and his colleague as the difference between the maximum and the minimum P-wave duration in 12-lead ECG [3]. Numerous studies have established the relationship between the PWD and an array of cardiovascular disorders such as paroxysmal atrial fibrillation, hypertension, and MS [5,7−8]. In healthy subjects, it was found that the PWD was correlated with age[9]. Also, the prolongation of P wave duration and the escalated PWD were related to increased risk of AF [3, 5]. Therefore, PWD has been considered as a crucial indicator to predict the AF risk in MS patients with sinus rhythm[5].
AF is a common clinical complication in MS patients. MS patients with AF were showed poor clinical prognosis, which was associated with the damage to the atrial contraction and fast ventricular rate[10]. Furthermore, secondary injury of the mitral valve and the inflammation of the atrium can aggravate the dilation of the left atrium and the degree of myocardial fibrosis[11]. The resulting anatomical abnormalities will lead to electrical heterogeneity, heterogeneous transmission speeds, and heterogeneous refractory phases within the atrial myocardium. It may also be accompanied by the atrial wall fibrosis and discordance of the atrial bundle, which was manifested as the increase of the P-wave duration and the PWD in ECG[2, 10] .
As compared to the healthy individuals, maximum P-wave duration, and PWD in MS patients were notably escalated, which suggested an increased risk of AF. In addition, a possibility of thromboembolism and mortality were significantly elevated in MS patients with AF. Hence, early detection of patients with MS by simple and acceptable method is a crucial step for the screen of MS patients in clinical practices. Previous studies showed some preliminary evidences on the relationship between ECG parameters and MS. Gholam and colleagues[12]found that the maximum P-wave duration was longer in patients with MS than that of matched controls, and the maximum P-wave duration was significantly correlated with the size of left atrium. More importantly, in a study with more than 3 years of long-term follow-up, unal et al.[13] revealed that the P-wave duration and PWD were increased with the development of MS further indicating the essential role of these two factors in the progression of MS. In this study, we revealed that in the absence of an echocardiographic evaluation, a prolonged P-wave duration and PWD would significantly contribute towards the early prognosis in MS patients. Also, a major advantage of this mode of prognosis is the low-cost of technology and the ease of evaluation.
Over the years, researchers have revealed the presence of increased sympathetic activity in MS patients[14, 15]. Moreover, Tukek et al.[16] demonstrated that the enhanced sympathetic excitation results in a remarkable rise in PWD. Besides, previous studies have shown[14] the reduced sympathetic excitation after the mitral valve surgery and the beneficial activity of beta-blockers in MS patients[17]. A chronic administration of beta-blockers could result in the reduced maximum P-wave duration and PWD in MS patients by constraining the sympathetic activity[17]. Thus, these findings suggest that enhanced sympathetic excitation could lead to the prolongation of maximum P-wave duration and PWD in MS patients.
We herein, for the first time, determined the cutoff value for P-wave duration as 119.50 ms and P-wave dispersion as 42.50 ms, for the effective prognosis of MS in the Chinese population. Our unpublished data showed that a regular ECG evaluation of patients with an increased risk of mitral valve abnormalities could delay the progression of mitral stenosis. However, this study demonstrated that the P-wave duration and PWD might not be enough for the prognosis of the degree of mitral stenosis in the Chinese population. Therefore, an in-depth analysis and validation studies are required to determine the predictive efficacy of P-wave duration and the PWD in the MS population. Nevertheless, global access to the affected patient’s clinical reports may help to unravel the mechanism of P-wave parameters and to access the increased risk of AF in MS patients.
This study, however, has certain limitations. Firstly, the sample size of the current research is comparatively small. Secondly, this study was a single-centered, observational study, which might have affected the generalizability. Thirdly, the ECG’s P-wave calculations were performed manually rather than employing the computer-assisted P-wave calculations. Finally, a selection bias may have occurred due to the delay in recording the onset of paroxysmal AF in the affected individuals.