Letter to the Editor
P-wave duration and dispersion in patients with obstructive sleep apnea

https://doi.org/10.1016/j.ijcard.2007.11.037Get rights and content

Abstract

Aim

P-wave dispersion (Pd) has been reported to be associated with inhomogeneous and discontinuous propagation of sinus impulses. The purpose of this study was to investigate Pd in patients with obstructive sleep apnea (OSA) and to determine its relationship with severity of the disease.

Methods

The study population included 67 patients referred to sleep laboratory. The Apnea–Hypopnea Index (AHI) was defined as the number of apneas and hypopneas per hour of sleep. Of the sixty-seven patients, 48 had AHI⩾5 and were diagnosed as OSA. Nineteen of the patients had AHI < 5 and were diagnosed as OSA (−) (Group 1), 32 of the patients had AHI between 5–30 (mild and moderate, group 2), 16 of the patients had AHI > 30 (severe, group 3). The P-wave duration was calculated in all leads of the surface electrocardiogram. The difference between the maximum (Pmax) and minimum P (Pmin) wave duration was calculated and was defined as the P-wave dispersion (Pd). Echocardiographic examination was also performed.

Results

Pmax was longer in group 3 compared to group 2 and group 1 (p = 0.002, p < 0.001 respectively). Pmax was longer in group 2 compared to group 1 (s < 0.001). Pd was greater in group 3 compared to group 2 and group 1 (p < 0.001 for both comparison). Pd was greater in group 2 compared to group 1 (p < 0.001). Pmin did not differ between the groups. In patients with OSA, Pd was positively correlated with AHI (r = 0.56, p < 0.001), BMI (r = 0.43, p = 0.03), and mitral early diastolic to late diastolic velocity (E/A) ratio (r = 0.37, p = 0.01). Multiple linear regression analysis showed that only AHI was independently associated with Pd (β = 0.39, p = 0.02).

Conclusion

Pd was found to be greater in patients with OSA than patients without OSA and to be associated with severity of the disease.

Introduction

Obstructive sleep apnea (OSA) is a condition characterized by repetitive pharyngeal collapse during sleep that leads to markedly reduced or absent airflow, followed by oxyhemoglobin desaturation, persistent inspiratory efforts against an occluded airway, and termination by arousal from sleep. It has been estimated that OSA affects 4% of middle-aged men and 2% of middle-aged women [1]. In a recent cross sectional study, an independent association between AF and OSA has been shown [2].

The prolongation of inta-atrial and inter-atrial conduction time and the inhomogeneous propogation of sinus impulses are well-known electrophysiological characteristics of the atrium prone to fibrillate and have been evaluated using two simple electrocardiographic (ECG) markers, maximum P-wave duration (Pmax) and P-wave dispersion (Pd) [3], [4], [5]. Increases of the P-wave duration and Pd has been used as a predictor of AF development in various clinical settings [4], [5], [6], [7], [8], [9]. To the best of our knowledge, P-wave duration and Pd have not been evaluated in patients with obstructive sleep apnea.

Section snippets

Methods

The study population consisted of sixty-seven patients referred to our sleep laboratory. The patients with any of the following were excluded from the study: prior pacemaker implantation, atrioventricular or intraventricular conduction disturbance, history of permanent or paroxysmal atrial fibrillation, pericarditis, valvular heart disease, pulmonary emboli, abnormal thyroid function, cardiomyopathies, pulmonary hypertension, abnormal serum electrolyte values, receiving any antiarrhythmic

Polysomnography

Obstructive sleep apnea was confirmed by polysomnography. The Apnea–Hypopnea Index (AHI) was defined as the number of apneas and hypopneas per hour of sleep. Patients with AHI < 5 were included in OSA (−) group 1, AHI 5-30 (mild and moderate) in group 2; AHI > 30 (severe) in group 3.

Electrocardiographic analysis

All subjects underwent a 12-lead ECG recording after a 20-min resting period in supine position at a paper speed of 50 mm/s and 2 mV/cm. The P-wave duration was measured manually in all simultaneously recorded 12 leads of the surface ECG by two of the investigators unaware of the study hypothesis. In each lead the mean values for the three complexes were calculated. The onset of the P-wave was defined as the point of first visible upward departure from baseline for positive waveforms, and as

Statistical analysis

All data were expressed as mean ± SD or frequency expressed as percent. Statistical analysis was carried out using a paired Student's t-test for continuous variables with the Statistical Package for Windows version 8.0 (SPSS Inc, Chicago, IL). To compare three groups of continuous variables, the 1-way analysis of variance with Bonferonni multiple comparison test was used. Associations of P-wave measurements with clinical, echocardiographic and polysomnographic variables were assessed by the

Results

Baseline clinical characteristics and polysomnographic measurements of the study population are shown in Table 1. Both systolic blood pressure and number of hypertensive patients in group with OSA (group 2 and 3) was higher than group 1. Both body mass index (BMI) and AHI of the group 3 was higher than group 2 and 1. AHI of group 2 was higher than group 1 (p < 0.001). Mean nocturnal oxygen saturation was higher in group 1 compared to group 3 and 2 (Table 1).

Mitral inflow early diastolic velocity

Discussion

The main findings of this study in patients with OSA are [1] Pd is significantly increased compared to patients without OSA and [2] Pd is related to AHI, hence the severity of the disease. This is the first study to evaluate the impact of OSA on Pd.

The maximum P-wave duration and Pd measured on ECG is an indicator of interatrial conduction disorder, and inhomogenous atrial conduction, respectively [5]. Previous studies have shown that Pmax and Pd can be used for prediction of AF in patients

Limitations

The study group involved a small number of patients. We manually calculated P-wave measurements by magnifying lens instead of computer-assisted P-wave calculations. However, our method has been used in previous studies [17], [18]. Our study group included patients without a history of AF, therefore the clinical significance of Pd was not evaluated in this study.

Conclusion

We have demonstrated that Pd is increased and correlated with severity of OSA, indicating that patients with severe OSA have more severe disturbance in atrial conduction. Underlying mechanisms and prognostic implications should be assessed in the future.

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