Discussion
In our study, the value of AEMD durations measured with the co-use of preoperative ECG and TTE (using TDI) in predicting PoAF was investigated in isolated CABG patients. It was found that the AEMD durations were statistically significantly longer in our group with PoAF. Although the difference between the groups in the LA antero-posterior diameters was not detected in TTE measurements, LA maximum volume was significantly higher in the group with PoAF. LV lateral Ea and LV medial Ea velocities were found to be lower in the group with PoAF, and this was an indication that diastolic dysfunction was more common in the group with PoAF. Also, LA lateral AEMD was found as an independent predictive factor in the multivariate logistic regression analysis we conducted to determine predictors for PoAF development.
PoAF is a cardiac arrhythmia that increases morbidity and mortality by affecting ventricular functions, causing hemodynamic impairment and increasing the risk of thromboembolic events. Its incidence after cardiac surgery is 20-40% (1). The PoAF incidence was 26.88% in our study, which included isolated CABG patients. Several studies were conducted to identify the risk factors of PoAF development. Advanced age, high body surface area, white ethnicity, hypertension, LV hypertrophy, use of preoperative digoxin, obstructive pulmonary disease, presence of postoperative LV diastolic and systolic dysfunction, preoperative high LA volume measurement, presence of postoperative low atrial filling fraction, and increased adrenergic drug use after surgery were associated with PoAF development (9-16). Also, the use of P wave duration with signal-averaged ECG to predict PoAF development was evaluated, and it was found that patients developing PoAF had preoperative prolonged P wave durations (17). In fact, when all these risk factors are evaluated, all of these parameters appear before usas the cause or result of atrial remodeling. Atrial remodeling triggers the development of PoAF by causing the development of multiple reentrant waves that initiate and possibly maintain AF (18).
The main finding of our study was that the AEMD durations measured by ECG and TTE (using TDI), which is a noninvasive method, was significantly longer in the group with PoAF. It is recently acknowledged that AEMD duration is a non-invasive evaluation method of atrial conduction time, and AEMD duration measurement is an easy, fast and reliable method. AEMD is defined as the delay between the detected electrical activity onset (P wave onset in superficial ECG) and the contraction in atrial myocardium (“late diastolic wave = Aa wave” evaluated with TDI). It was emphasized in many studies that the prolongation of AEMD durations was the independent marker of new-onset or recurrent AF (19-21). Determining the P wave duration in signal-averaged ECG is also useful for predicting the atrial electromechanic conduction times, but its use in clinical practice is limited because it requires special equipment, and evaluation of its results is time-consuming. However, AEMD, which is a new echocardiographic parameter, was confirmed to be correlated with P wave durations detected by using signal-averaged ECG (17,20).
In a study conducted by Özlü et al., it was reported that LA maximum volume and AEMD duration were the independent predictors of PoAF development after CABG surgery (23). Although their results support the results of our study, unlike our study, only inter-atrial electromechanical delay (the difference between LV lateral AEMD and RV lateral AEMD) was evaluated in this study. In another study conducted by Fujiwara et al., 88 off-pump CABG patients were included, AEMD durations were measured with preoperative TTE (using TDI), and in addition, left atrial volume index (LAVI) was calculated (24). Patients were monitored with ECG telemetry for 7 days postoperatively. As a result, they concluded that PoAF was detected in 35 patients (39.8%), and the AEMD duration (OR: 1.11, 95% CI: 1.06-1.16, p = 0.0001) and LAVI (OR: 1.11, 95% CI: 1.02–1.20, p = 0.01) were independent predictors of PoAF development with multivariate logistic regression analysis. They also conducted ROC Curve Analysis, and reported that AUC: 0.85 for AEMD (sensitivity: 74.3% and specificity: 86.8%) (23). Although a different CABG technique was applied in this study compared to our study, our results were similar. In our study, we also found the LA lateral AEMD was an independent predictive factor for PoAF development (OR: 1.03, 95% CI: 1,001-1.06, p=0.04); and AUC: 0.741 for LA lateral AEMD in ROC Curve analysis (95% CI: 0.633-0.849, p <0.001). LA lateral AEMD duration is significantly correlated with LA diameter and LA maximum volume (25). These data may explain the importance of AEMD durations, which is an indicator of pathological changes in the atrium, for predicting PoAF. The LV lateral AEMD parameters were not included the univariate and multivariate analysis because EMD parameters were similar in atrial and ventricular site.
There are limited studies emphasizing the importance of AEMD in predicting the development of PoAF in other cardiac operations such as aortic valve and mitral valve surgeries (26,27). Takahashi et al. monitored patients who underwent aortic valve replacement with ECG telemetry for 7 days, and reported that the PoAF incidence was as high as 65% (41 of 63 patients). They measured the AEMD duration with preoperative TTE (using TDI), and concluded that it was an independent predictor for the development of POAF (OR: 1.07, 95% CI: 1.02–1.13; p = 0.0072) (24). In the same center, PoAF development was investigated in patients with mitral valve replacement due to mitral stenosis, and as a result, LA lateral AEMD duration was found to be an independent predictor for the development of POAF (OR, 1.04; 95% CI: 1.01–1.07; p = 0.0048). Also, in ROC Curve Analysis, the AEMD duration cut-off value for the development of POAF was reported as 159.4 ms (27). Unlike our study, in these studies, the AEMD time was taken as the time between the P wave start at ECG and the mitral lateral Aa peak point measured with TDI; however, in our study, the time between the onset of the mitral lateral Aa was measured.
In the present study, it was concluded that advanced age, hypertension, LA maximum volume height and the increase in LA lateral AEMD, which is a marker of diastolic heart failure, are risk factors for the development of PoAF. The presence of LV diastolic dysfunction in predicting PoAF development comes to the forefront in many studies unlike LV systolic dysfunction (16, 19). In our study, we believe that the significantly lower LV lateral Ea and LV medial Ea velocities, among the parameters indicating LV diastolic function in the group with PoAF, is the probable cause of high PAP and diuretic usage rates in the group with PoAF. In their prospective study that included 275 elective CABG patients, Gibson et al. reported that LV systolic function was not an independent predictive factor for PoAF (19). Similarly, in our study, EF values were similar in groups with and without PoAF.
Our study had some limitations. One of the limitations of the study was that it had a single-centered, and non-randomized design with a relatively low number of patients. Another limitation was that our results are limited to postoperative new-onset, in-hospital AF, and the development of PoAF after the patients were discharged was not evaluated. Also, the development of PoAF is multifactorial; and it was another limitation that only parameters that had possible major impacts (e.g. age, hypertension, conventional TTE and TDI measurements, etc.) were included in the statistical evaluation of our study data. For this reason, the predictive effect of AEMD durations on the development of PoAF must be confirmed with broader prospective studies with longer follow-up times in patients undergoing CABG.