Identifying early left atrial dysfunction in individuals with obstructive sleep apnea: The role of the morphology-voltage-P wave duration electrocardiography score

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RESEARCH ARTICLE

Hippokratia 2024, 28(3): 93-99

Küçük U1, Mutlu P2, Mirici A2, Özpınar U1, Özpınar SB2
1Department of Cardiology
2Department of Chest Diseases
Faculty of Medicine, Çanakkale Onsekiz Mart University, Canakkale, Turkey

Abstract

Background: Obstructive sleep apnea (OSA) can lead to left atrial (LA) dysfunction, which increases the risk of severe heart problems such as atrial fibrillation and heart failure. Early detection of LA dysfunction is essential to prevent these complications. We investigated whether the new morphology-voltage-P wave duration electrocardiography (MVP ECG) level could effectively identify early-stage LA functional abnormality in OSA individuals, as current diagnostic techniques have limitations.

Methods: We studied a sample of 120 OSA patients using speckle-tracking echocardiography to assess LA function. After the echocardiography exam, we divided these individuals into two groups: those with regular LA and those with impaired LA functions. Our main measure of LA function was peak atrial longitudinal strain (PALS).

Results: We found significant differences in PALS values between groups (p <0.001) despite having an equivalent LA size, suggesting occult LA dysfunction in OSA patients. The MVP ECG score proved effective in identifying LA dysfunction caused by changes in atrial structure (sensitivity: 89 %, specificity: 63 %, AUC: 0.862).

Conclusions: The MVP ECG score is a promising non-invasive method to detect early atrial changes in OSA patients. Using this score in regular medical care could help physicians intervene earlier, potentially reducing the risk of heart problems in these high-risk individuals. HIPPOKRATIA 2024, 28 (3):93-99.

Keywords: Left atrial function, 12-lead electrocardiogram, strain echocardiography

Corresponding author: Uğur Küçük, MD, Associate Professor, Çanakkale Onsekiz Mart University, Faculty of Medicine, Research and Training Hospital, Barbaros Mahallesi Prof. Dr. Sevim BULUÇ Sokak No 2, Çanakkale, Turkey, tel: +905345911902, e-mail: drugurkucuk@hotmail.com

Introduction

When the upper airway repeatedly collapses during sleep, subjects suffer obstructive sleep apnea (OSA), resulting in periods of reduced or blocked airflow1. This condition significantly raises the possibility of potential cardiovascular and cerebrovascular problems2. Studies show that OSA leads to ventricular hypertrophy and diastolic dysfunction3,4, which affect the anatomy and functions of the left atrium (LA)5. The condition also disrupts atrial conduction by causing structural changes and increased strain on the atria6.

Electrocardiography (ECG) remains an essential diagnostic tool in assessing atrial function. Several ECG markers are indicative of LA remodeling and dysfunction, including changes in P-wave characteristics (dispersion and persistence), abnormal terminal force in lead V1, and interatrial block (IAB)7,8. The relationship between these markers, particularly IAB and P wave disturbances, and LA strain measurements suggests their value as indicators of atrial dysfunction9. Recently, researchers have developed the Morphology-Voltage-P wave persistence electrocardiography (MVP ECG) value, which combines measurements of P wave persistence, voltage, and the presence of IAB10. This new scoring system is promising in assessing structural and electrical atrial abnormalities.

Since OSA-related LA remodeling is likely to affect atrial conduction, we expect to find corresponding changes in patients’ ECG patterns. Thus, our investigation aims to evaluate how well the MVP ECG score detects early onset of LA dysfunction, using speckle-tracking echocardiography for confirmation. This research may help clinicians identify early cardiac changes in OSA patients and intervene before complications develop.

Materials and Methods

Our study enrolled 120 OSA patients who underwent polysomnography (PSG) at the Sleep Laboratory of Çanakkale 18 mart University between March 2023 and June 2024, with all participants demonstrating normal sinus rhythm during the study. Patient selection focused on those with a PSG-confirmed diagnosis of OSA, while carefully screening out individuals with various complicating conditions.

We excluded individuals having uncontrolled hypertension (HT), uncontrolled diabetes mellitus (DM), those with a record of coronary artery problems, and those having a left ventricular ejection fraction (LVEF) of less than 50 %. Additional exclusions included patients with ventricular hypertrophy [determined by left ventricular mass index (LVMI) ≥150 g/m² on echocardiography], renal insufficiency [glomerular filtration rate (GFR) below 60 mL/min], and any record of ablation or atrial fibrillation (AF). We also excluded cases with pulmonary embolism, malignancy, substantial valvular disease, systemic inflammatory illness, liver dysfunction, or bundle branch blockage with QRS complexes greater than 120 ms. Individuals having thyroid dysfunction, low quality echocardiograms, people under the age of 18, and those with unclear or overlapping diagnoses of chronic obstructive pulmonary disease or asthma were among the other exclusion criteria.

All subjects provided written informed permission, and the investigation was conducted in compliance with the Declaration of Helsinki’s tenets with the Çanakkale 18 Mart University Clinical Research Ethics Committee approval (decision No: 2023/04-07, date: 22/02/2023).

Overnight PSG was performed using the Neuron-Spectrum-5 device (Neurosoft, Ivanova, Russia) under the continuous supervision of a sleep technician. The comprehensive PSG setup monitored multiple parameters through different channels: electrooculogram (two channels), electroencephalogram (six channels), submental electromyogram (two channels), and anterior tibial electromyography for both legs (two channels). We also recorded single-channel electrocardiogram data, along with airflow measurements using an oro-nasal pressure-adjusted cannula, respiratory inductance plethysmography for chest and abdominal movements, and arterial oxygen saturation using finger pulse oximetry (SaO2: one channel). Using established standards, respiratory events and sleep phases were assessed11. We defined apnea as a complete absence of airflow lasting 10 seconds or more, whereas hypopnea was identified by an airflow reduction of 30 % or more from baseline for a minimum of 10 seconds, accompanied by either a 3 % or greater drop in oxygen saturation or stimulus. The overall number of apnea and hypopnea episodes per hour of sleep was used to compute the apnea-hypopnea index (AHI). An AHI of five or above and relevant symptoms12 were necessary for an OSA diagnosis; severity was divided into three categories: severe (AHI >30), moderate (AHI: 15-30), and mild (AHI: 5-14).

A typical 12-lead resting ECG recording was performed on each patient, using specific technical parameters: filter range of 0.5-150 Hz, AC filter at 60 Hz, paper speed 25 mm/s, and amplitude of 10 mm/mV. Two cardiologists, blinded to patient clinical information, analyzed the ECG recordings using Image J software to examine 10x magnified images.

Evaluation of the MVP ECG score included three key elements: P-wave duration, morphology, and voltage measurements.

P-wave duration

This is described as the time interval between the point at which the P-wave deviates from the baseline and the point at which it returns to the baseline. The scoring criteria are as follows13,14: zero points if the duration is less than 120 ms, one point if the duration is 120-140 ms, and two points if the duration is greater than 140 ms.

P-wave morphology

Scoring is based on the existence and severity of IAB as observed in the leads (II, III, and aVF): zero points if there is no IAB, one point if there is partial IAB, and two points if there is advanced IAB.

P-wave voltage

The P-wave voltage is measured during the T-P interval in lead I from the peak to the isoelectric line. The scoring is as follows: zero points if PVL1 >0.20 mV, one point if PVL1 is between 0.10 and 0.20 mV, and two points if PVL1 <0.10 mV.

Blood pressure measurements were obtained immediately before the echocardiographic assessment via the Vivid 7 Pro system (GE, Vingmed, Horten, Norway). Two experienced cardiologists performed the assessments of LVEF, LA size, and other parameters while remaining blinded to the study data.

To analyze LA strain, we traced the LA endocardium in both apical four-chamber and two-chamber views employing Echo PAC software (General Electric, Horten, Norway). Our protocol maintained a frame rate of more than 50 frames/sec, with strain measurements synchronized to the R-R interval on the ECG. The endocardial outline of the LA was carefully mapped at the end of ventricular systole using apical four-chamber (A1) and two-chamber (A2) views. To calculate LA volume, we applied the formula [(0.85) x (A1 x A2 /LA length)] and then derived the left atrial volume index by normalizing LA volume to body surface area15. End-systolic LA strain, also known as peak atrial longitudinal strain (PALS), was noted at the QRS complex peak on the ECG16,17. In defining LA strain based on end-systolic contours, we specifically excluded pulmonary veins and the LA appendage from our measurements. The PALS, which represents the maximum atrial strain during the cardiac cycle, serves as a critical indicator of LA reservoir function18. Based on previous large-scale validation studies, we used a cut-off value of 23 % to identify early LA dysfunction19,20.

Statistical Analysis

We used the G*Power program, Version 3.1.9.6, to do the power analysis and determined the necessary sample at 90 people for 85 % power at the 5 % alpha level. We evaluated data with the IBM SPSS Statistics for Windows, Version 19.0. (IBM Corp., Armonk, NY, USA). The findings are displayed as the median with interquartile range (IQR) or mean ± standard deviation. A number (n) and a percentage (%) represent the nominal variables. The Student’s t-test was utilized for data that was regularly distributed, while the Mann-Whitney U test was employed for data that was not. The chi-square test or Fisher’s exact test, if appropriate, were used to analyze categorical variables. We conducted correlation analysis using both Pearson and Spearman correlation tests. The best cut-off value for the MVP ECG score in predicting LA dysfunction was found using a receiver operating characteristic (ROC) curve. The Youden J index was utilized to determine the sensitivity and specificity. Univariate analysis identified the potential confounding variables that would entered in the multivariate analysis if they had a p-value <0.1. Independent predictors of LA dysfunction in OSA participants were determined using multivariate analysis. The Hosmer-Lemeshow test was used to evaluate model fit. The statistical significance level was set at p <0.05.

Intra- and Interobserver Variability

The intraclass correlation coefficients (ICCs) for intraobserver and interobserver variabilities in echocardiographic parameters were 0.843 [95 % confidence interval (CI): 0.623-0.957] and 0.870 (9 5% CI: 0.648-0.972), respectively.

Result

We created two groups from the 120 participants based on their LA function. Sixty-five individuals in the initial group had normal LA function, while the second group comprised 55 patients exhibiting abnormal LA function (Table 1). Patients with abnormal LA function exhibited a significantly longer duration of OSA (6.29 ± 1.58 years vs 3.18 ± 1.65 years, p <0.001). Furthermore, the AHI was significantly greater in the abnormal LA function group (16.47 ± 1.13 vs 11.88 ± 0.78, p <0.001) (Table 1).

Regarding echocardiographic measurements, LVMI was significantly lower in the normal LA function group (80.34 ± 10.32 vs 74.93 ± 8.06, p =0.002). PALS was significantly reduced in the abnormal LA function group (19.34 ± 2.93 vs 28.78 ± 1.82, p <0.001) (Table 2).

Table 3 depicts the relationship between the MVP ECG level, PALS, and some other clinical parameters. The scores demonstrated a positive correlation between the MVP ECG score and age (r =0.45, p =0.002) and OSA duration (r =0.52, p =0.001). In contrast, a significant negative correlation was observed between PALS and these parameters (r =-0.41, p =0.004 for age; r =-0.55, p <0.001 for OSA duration). Moreover, a robust inverse correlation was identified between PALS and the MVP ECG value (r =-0.67, p <0.001), suggesting that elevated MVP ECG scores are associated with reduced PALS values, indicative of declining LA function (Table 3).

Table 4 delineates the distribution of MVP ECG scores and PALS values based on the severity of apnea. Both the MVP ECG value and the PALS measurement demonstrated a significant correlation with the severity of OSA. The mean score on the MVP ECG was significantly enhanced in participants having severe OSA (3.5 ± 0.7) compared to those with mild (1.2 ± 0.4) and moderate OSA (2.1 ± 0.5) (p <0.001). Similarly, PALS was observed to be lower in patients with severe OSA (19.3 ± 3.0) in comparison to those with mild (27.8 ± 2.1) and moderate OSA (24.6 ± 2.6) (Table 4) (p <0.001).

Multivariate logistic regression analysis was employed to assess variables such as age, DM record, HT record, LVMI, OSA duration, and MVP ECG score, which showed statistical significance in univariate studies. As independent predictors of early LA dysfunction, the study found that the MVP ECG score [Odds ratio (OR): 3.090, 95 % CI: 1.795-5.318, p <0.001] and OSA duration (OR: 1.532, 95 % CI: 1.156-2.032, p =0.003) (Table 5).

An MVP ECG score greater than 1.5 was predictive of aberrant LA function with a 63 % specificity and an 89 % sensitivity, according to ROC curve analysis [area under the curve (AUC): 0.862; p <0.001] (Figure 1).

Figure 1: Receiver operating characteristic curve analysis of the morphology-voltage-P wave duration electrocardiography score to predict early left atrial dysfunction.
ROC: receiver operating characteristic, MVP ECG: morphology-voltage-P wave duration electrocardiography, AUC: area under the curve.

Discussion

We demonstrated in this research that both the OSA duration and MVP ECG score may represent innovative tools for identifying early-stage LA dysfunction in individuals with OSA. OSA is widely acknowledged as a systemic condition with substantial extrapulmonary consequences, including cardiovascular problems21. In addition, OSA has been well-documented as a substantial and standalone risk element for AF development22, not only increasing its likelihood but also affecting atrial electromechanical properties, as well23. The observed atrial electromechanical delay in individuals with OSA shows the presence of underlying atrial myopathy, which reflects disruptions in atrial conduction and mechanical function. Prior studies have implicated factors such as inflammatory process, autonomic dysfunction, and structural remodeling, common in OSA, as contributors to atrial myopathy and the resulting electromechanical abnormalities24. Consistent with these findings, the present study identified OSA duration as a standalone signal for early pathology in LA.

ECG offers indirect insights into LA size and function25,26. Previous research has highlighted strong associations between P-wave indices on ECG and LA pathology or fibrosis in individuals having IAB27. The findings of this current research align with these studies, demonstrating significant variations in P-wave morphology, voltage, and duration among groups with varying LA functionalityRecently, a group of researchers proposed the MVP ECG value as a newfangled tool for assessing the atrium’s structural and electrical alterations10. IAB, characterized by retarded electrical conduction between the atria, is easily detectable on ECG and has been linked to atrial arrhythmias28. Moreover, despite its function in electrical conduction, P-wave voltage may reflect atrial myocardial mass, with previous studies associating right atrial growth in AF individuals with higher vascular risk29. The growing body of evidence supports the MVP ECG value as a reliable predictor of LA dysfunction14,30,31, and our findings further underscore its utility in detecting LA pathology in individuals with OSA.

It is possible to evaluate LA functions via several techniques, with speckle-tracking echocardiography being widely utilized in clinical practices for detecting pathology before the onset of structural changes. PALS has been nearly linked with AF evolution and LA pathology32. In this study, decreased contraction of LA was linked to a significant reduction in PALS, as evidenced by markedly lower PALS levels in the reduced LA function group in comparison to the normal functioning group. Also, a significant negative relation between MVP ECG levels and PALS scores underscores the utility of this score in determining atrial damages and restructuring.

There are several restrictions on this investigation. Our findings may not be as generalizable because of the comparatively small sample size. However, a notable strength is identifying the MVP ECG level as a newfangled, non-invasive method for identifying LA dysfunction early in OSA individuals. The high interobserver and intraobserver reliability of the echocardiographic measurements further supports the validity of our results. While advanced imaging modalities, including cardiac magnetic resonance imaging, could offer more accurate assessments of the anatomy and function of the atrium, the use of echocardiography in this study remains a practical limitation. Additionally, although the MVP ECG score demonstrates promise, it is crucial to bear in mind that OSA is a diverse disorder with a range of symptoms and severities. To reduce confounding factors, this study excluded patients with comorbidities known to influence atrial remodeling, such as asthma. Future studies should investigate the impact of different OSA phenotypes on atrial remodeling.

Our results suggest that the MVP ECG level integrates multiple electrocardiographic parameters and is a valuable tool for detecting LA dysfunction associated with LA tissue damage and restructuring in OSA individuals. Despite equal LA diameters across patient groups, the considerable variations in PALS results show that OSA patients have subclinical LA pathology.

Conflict of Interest

No conflicts of interest was declared by the authors.

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