Comparison of Cardiac Repolarization After Transcatheter Aortic Valve Implantation and Surgical Aortic Valve Replacement: A Longitudinal Study

Standard 12-lead ECG recordings were obtained from patients at a paper speed of 25 mm/s. The RR interval, QT interval, corrected QT (QTc) interval, QTD, QTcD, TpTe interval, TpTe/QT ratio, and TpTe/QTc ratio were manually measured in the ECG recordings. The QT interval in leads II and V5 was measured using the tangent method, and it was considered as the interval from the onset of the Q wave, which was defined as the intersection of a threshold level with the differential of the Q wave, to the end of the T wave, which was defined as the intersection of a tangent to the steepest slope of the last limb of the T wave and the baseline (Fig. 1). The QTc interval was calculated using Fridericia’s formula (QTc = QT/3√RR). The TpTe interval was measured as the interval from the peak of the T wave to the end of the T wave in lead II. The end of the T wave was determined using the tangent method. Three consecutive cycles in lead II were measured and averaged for analysis of the RR interval, QT interval, and TpTe interval. The QTD was defined as the difference between the maximum and minimum mean QT interval on 12-lead ECG. The mean value of data derived from three successive beats for each lead was used for analysis. Leads in which the end of the T wave could not be clearly detected were excluded from the study. The investigator who measured these values was blinded to group allocation (TAVI or SAVR group). The ECG recordings were performed before the surgery, immediately after surgery, and 1 month, 3 months, and 6 months after surgery in both groups.

Data are expressed as mean ± standard deviation. Patient characteristics were analyzed using the Mann–Whitney U test, Fisher’s exact test, and Chi-square test as appropriate. The RR interval, QT interval, QTc interval, QTD, QTcD, TpTe interval, TpTe/QT ratio, and TpTe/QTc ratio were analyzed using the Mann–Whitney U test and analysis of co-variance (ANCOVA) after adjustment of age, sex, and duration of hospitalization. These statistical analyses were performed using IBM SPSS 24.0 (IBM Japan, Tokyo). In all analyses, the probability to detect a significant difference was set at 5% (P < 0.05).

No significant differences in QT and QTc between TAVI and SAVR were observed in the present study. However, QTc, but not QT, was slightly increased immediately after surgery as compared to pre-surgery in both the groups. We also observed decreased RR interval immediately after surgery in both the groups. However, these RR changes recovered on postoperative day 1. The QTc may be overcorrected due to tachycardia after the surgery. Sinus tachycardia, which may be caused by release of catecholamine in response to surgical stress or anemia, is common and subsides within a few days after the surgery. A postoperative tachycardia should not be dismissed within the first 4 days post-surgery [9].

In the present study, QTD and QTcD remained high immediately after surgery in the SAVR group, whereas QTD and QTcD in the TAVI group decreased. These differences in QTD and QTcD eliminated 1 month after surgery. QTD is increased in most patients with AS and these changes are weakly related to the degree of left ventricular hypertrophy [4]. Several studies have shown that increased QTD due to AS, which is associated with the risk of ventricular arrhythmia, decreases after TAVI [7, 10]. Our findings also confirmed that prolonged QTD and QTcD rapidly decline after TAVI treatment, whereas SAVR slowly recovers QTD and QTcD. TAVI might therefore imply a higher postoperative arrhythmia risk than SAVR. However, in our cohort of n = 45 patients undergoing TAVI, none experienced early postoperative ventricular arrhythmias.

The peak of the T wave depicts the end of the epicardial action potential and the end of the T wave shows the M cell action potential (mid-myocardium). Hence, the action potential duration of the longest M cell determines the TpTe interval and serves as an index of TDR [11]. Similar to TpTe, the TpTe/QT ratio is a significant marker for evaluating the TDR under the conditions of long QT, short QT, Brugada syndrome, and acute ST-segment elevation [6]. In addition, TpTe, TpTe/QT, and TpTe/QTc exhibited a positive correlation with mean aortic gradient, and might be a predictor of AS severity [12]. Our findings indicate that TpTe, TpTe/QT, and TpTe/QTc were not prolonged in either the TAVI or SAVR groups, whereas QTD and QTcD were increased in the SAVR group, but not in the TAVI group. The contradiction between QTD, which shows the spatial distribution of repolarization, and TpTe, which shows the TDR, has been uncertain in the present study. Our hypotheses for this contradiction are as follows: (1) spatial inhomogeneity might be more susceptible to hypoperfusion (endocardial or subepicardial damage) compared to transmural inhomogeneity (a higher degree of myocardial damage), (2) the sample size of this study might be insufficient to detect the transmural inhomogeneity, (3) to detect the accurate transmural inhomogeneity, we might have to measure multiple TpTe or dispersion of TpTe [13]. To clarify the clinical significance of QTD and TpTe, further studies are needed.

The long-term outcome of TAVI and SAVR remain controversial. In the short term, mortality and hospitalization are better in TAVI as compared to SAVR [1]. However, after 1 year, mortality worsened in the TAVI group as compared to SAVR [14]. To clearly determine the effect of TAVI on cardiac repolarization, long-term comparison between TAVI and SAVR is essential.

There was a significant difference in QT in lead V5 at 3 months. Such a statistical difference might arise from the reduction of participants in the late perioperative period of this observation. In our observation, the number of patients whose ECGs were obtained were gradually reduced, especially in SAVR (at 3 months: n = 15, at 6 months: n = 14) because of the transfer to another hospital. At 3 and 6 months, it was difficult to compare the ECG parameters in the present study. Further studies and accumulation of long-term outcomes are needed to determine the benefit of TAVI.