Left Atrial Appendage Amputation for Atrial Fibrillation during Aortic Valve Replacement.

BACKGROUND: Occluding the left atrial appendage (LAA) during cardiac surgery reduces the risk of ischemic stroke; nonetheless, it is currently only softly recommended with "may be considered" by the current guidelines. We aimed to assess thromboembolic risk after LAA amputation in patients with atrial fibrillation (AF) and aortic stenosis undergoing biological aortic valve replacement (AVR) as primary cardiac surgery. METHODS: Two cohorts were generated retrospectively: patients with AF undergoing AVR alone or combined with revascularization either with LAA amputation or without. Data were collected from the hospital-specific data system. Follow-up was completed by telephone interview or in person. Thirty-day and follow-up results were compared in patients with vs. without LAA amputation. RESULTS: One hundred and fifty-seven patients were investigated retrospectively, and seventy-four pairs were matched with regard to baseline characteristics. Patients with LAA amputation exhibited a lower incidence of cumulative and late ischemic stroke (6.4% vs. 25%, p = 0.028 and 3.2% vs. 20%, p = 0.008, respectively; hazard ratio 0.30; 95% confidence interval 0.11; 0.84; p = 0.021) during follow-up of 48 months vs. patients without intervention during follow-up of 45 months, p = 0.494. No significant differences were observed in postoperative stroke, 2 (2.7%) vs. 3 (4.1%), p = 1.000, re-exploration for bleeding 3 (4.1%) vs. 6 (8.1), p = 0.494 or late pericardial effusion 2 (2.7%) vs. 3 (4.1%), p = 1.000, in-hospital 2 (2.7%) vs. 4 (5.4%), p = 0.681 and all-cause mortality 15 (23.8%) vs. 9 (15%), p = 0.315 in patients with vs. without LAA amputation, respectively. CONCLUSIONS: A combination of leading aortic stenosis and AF in patients undergoing isolated or combined biological AVR represents a subpopulation with excessive thromboembolic risk. Concomitant LAA amputation during cardiac surgery reduces the risk of ischemic stroke without posing an additional periprocedural risk for the patient. Therefore, the minimal invasive approach at the expense of omitting LAA amputation should be discouraged to maximize the clinical benefits of AVR in this setting.

Improved creatinine-based early detection of acute kidney injury after cardiac surgery.

OBJECTIVES: This study aims to improve early detection of cardiac surgery-associated acute kidney injury (CSA-AKI) compared to classical clinical scores. METHODS: Data from 7633 patients who underwent cardiac surgery between 2008 and 2018 in our institution were analysed. CSA-AKI was defined according to the Kidney Disease Improving Global Outcomes (KDIGO) criteria. Cleveland Clinical Score served as the reference with an area under the curve (AUC) 0.65 in our cohort. Based on that, stepwise logistic regression modelling was performed on the training data set including creatinine (Cr), estimated glomerular filtration rate (eGFR) levels and deltas (ΔCr, ΔeGFR) at different time points and clinical parameters as preoperative haemoglobin, intraoperative packed red blood cells (units) and cardiopulmonary bypass time (min) to predict CSA-AKI in the early postoperative course. The AUC was determined on the validation data set for each model respectively. RESULTS: Incidence of CSA-AKI in the early postoperative course was 22.4% (n = 1712). The 30-day mortality was 12.5% in the CSA-AKI group (n = 214) and in the no-CSA-AKI group 0.9% (n = 53) (P < 0.001). Logistic regression models based on Cr and its delta gained an AUC of 0.69; 'Model eGFRCKD-EPI' an AUC of 0.73. Finally, 'Model DynaLab' including dynamic laboratory parameters and clinical parameters as haemoglobin, packed red blood cells and cardiopulmonary bypass time improved AUC to 0.84. CONCLUSIONS: Model DynaLab' improves early detection of CSA-AKI within 12 h after surgery. This simple Cr-based framework poses a fundament for further endeavours towards reduction of CSA-AKI incidence and severity.

Serum Klotho as a marker for early diagnosis of acute kidney injury after cardiac surgery.

BACKGROUND: Early diagnosis of acute kidney injury (AKI) after cardiac surgery is based on serum creatinine which is neither a specific nor a sensitive biomarker. In our study, we investigated the role of serum Klotho in early prediction of AKI after cardiac surgery using cardiopulmonary bypass (CPB). METHODS: The included patients were classified into three groups according to AKI stages using KDIGO criteria. The measurements of creatinine and Klotho levels in serum were performed before surgery, at the end of CPB, 2 hours after the end of CPB, 24 hours and 48 hours postoperatively. RESULTS: Seventy-eight patients were included in the study. A significant increase of creatinine levels (p<0.001) was measured on the first day after the surgery in both AKI groups compared to the non-AKI group. However, a significant difference between AKI-2 and AKI-1 groups (p=0.006) was not measured until the second day after the operation. Using decision trees for classification of patients with a higher or lower risk of AKI we found out that Klotho discriminated between the patients at low risk of developing more severe kidney injury in the first hours after surgery and the patients at high risk better than creatinine. Adding also the early measurements of creatinine in the decision tree model further improved the prediction of AKI. CONCLUSIONS: Serum Klotho may be useful to discriminate between the patients at lower and the patients at higher risk of developing severe kidney injury after cardiac surgery using CPB already in the first hours after surgery.

Two approaches-one phenomenon-thrombocytopenia after surgical and transcatheter aortic valve replacement.

BACKGROPUND AND AIM: Postoperative thrombocytopenia after surgical aortic valve replacement (SAVR) or transcatheter aortic valve replacement (TAVR) and aggravating causes were the aim of this retrospective study. METHODS: Data of all patients treated with SAVR (n = 1068) and TAVR (n = 816) due to severe aortic valve stenosis was collected at our center from 2010 to 2017. Preprocedural and postprocedural values were collected from electronic patient records. RESULTS: There was a significant drop in platelets in both groups, the TAVR group showed overall superior platelet preservation compared to the AVR group (P < .001). In the SAVR subgroup analysis, a significant difference in platelet preservation was observed between the valve types (P < .001), particularly with the Freedom SOLO valve. In the TAVR subgroup analysis, the valve type did not influence platelet count (PLT) reduction (P = .13). In the SAVR subgroup analyses, PLT was found to be worsened with cardiopulmonary bypass (CPB) duration. CONCLUSION: Thrombocytopenia frequently occurs after implantation of a biological heart valve prosthesis, with a higher frequency observed in patients after cardiac surgery rather than TAVR. Although some surgical bioprosthetic models are more susceptible to this phenomenon, CPB duration seems to be a major determinant for the development of postoperative thrombocytopenia.

Aortic valve calcification as a risk factor for major complications and reduced survival after transcatheter replacement.

BACKGROUND: Aortic valve calcification is supposed to be a possible cause of embolic stroke or subclinical valve thrombosis after transcatheter aortic valve replacement (TAVR). We aimed to assess the role of aortic valve calcification in the occurrence of in-hospital clinical complications and survival after TAVR. METHODS: We retrospectively analyzed preoperative contrast-enhanced multidetector computed tomography scans of patients who underwent TAVR on the native aortic valve in our center. Calcium volume was calculated for each aortic cusp, above and below the aortic annulus. Outcomes were recorded according to VARC-2 criteria. RESULTS: Overall, 581 patients were included in the study (SapienXT = 192; Sapien3 = 228; CoreValve/EvolutR = 45; Engager = 5; Acurate = 111). Median survival was 4.98 years (interquartile range 4.41-5.54). Logistic regression identified calcium load beneath the right coronary cusp in left ventricular outflow tract (LVOT) as significantly associated with stroke (odds ratio [OR] 1.2; 95% confidence interval [CI] 1.03-1.3; p = 0.0019) and in-hospital mortality (OR 1.1; 95% CI 1.004-1.2; p = 0.04), whereas total calcium volume of the LVOT was associated with both in-hospital and 30 day-mortality (OR 1.2; 95% CI 1.01-1.4; p = 0.03, and OR 1.2; 95% CI 1.02-1.43; p = 0.029, respectively). Cox regression identified total calcium of LVOT (hazard ratio [HR] 1.18; 95% CI 1.02-1.38; p = 0.026), male sex (HR 1.88; 95% CI 1.06-3.32; p = 0.031), baseline creatinine clearance (HR 0.96; 95% CI 0.93-0.98; p < 0.001), and baseline severe aortic regurgitation (HR 7.48; 95% CI 2.76-20.26; p < 0.001) as risk factors associated with lower survival. CONCLUSION: LVOT calcification is associated with increased risk of peri-procedural stroke and mortality as well as shorter long-term survival.

Cardiac autonomic regulation and PR interval determination for enhanced atrial fibrillation risk prediction after cardiac surgery.

BACKGROUND: Changes in cardiac autonomic regulation and P-wave characteristics are associated with the occurrence of atrial fibrillation. The purpose of this study was to evaluate whether combined preoperative non-invasive determination of cardiac autonomic regulation and PR interval allows for the identification of patients at risk of new-onset atrial fibrillation after cardiac surgery. METHODS: RR, PR and QT intervals, and linear and non-linear heart rate variability parameters from 20 min high-resolution electrocardiographic recordings were determined one day before surgery in 150 patients on chronic beta blockers undergoing elective coronary artery bypass grafting, aortic valve replacement, or both, electively. RESULTS: Thirty-one patients (21%) developed postoperative atrial fibrillation. In the atrial fibrillation group, more arterial hypertension, a greater age, a higher EuroSCORE II, a higher heart rate variability index (pNN50: 9 ±â€¯20 vs. 4 ±â€¯10, p = 0.050), a short PR interval (156 ±â€¯23 vs. 173 ±â€¯31 ms; p = 0.011), and a reduced short-term scaling exponent of the detrended fluctuation analysis (DFA1, 0.96 ±â€¯0.36 vs. 1.11 ±â€¯0.30 ms; p = 0.032) were found compared to the sinus rhythm group. Logistic regression modeling confirmed PR interval, DFA1 and age as the strongest preoperative predictors of postoperative atrial fibrillation (area under the receiver operating characteristic curve = 0.804). CONCLUSIONS: Patients developing atrial fibrillation after cardiac surgery presented with severe cardiac autonomic derangement and a short PR interval preoperatively. The observed state characterizes both altered heart rate regulation and arrhythmic substrate and is strongly related to an increased risk of postoperative atrial fibrillation.

Efficacy of sutureless aortic valves in minimally invasive cardiac surgery: an evolution of the surgical technique.

BACKGROUND: Sutureless aortic valve prostheses have the potential of shortening surgical time, but if this results in improved clinical outcome remains to be determined. The aim of this study was to compare the outcome of patients undergoing conventional vs. minimally invasive AVR, with either a stented or sutureless bioprosthesis. METHODS: From 2007 to 2015, 627 patients underwent elective isolated AVR and were divided into three groups: patients who underwent sutureless-AVR via J sternotomy (group A, N.=206) and patients who underwent stented-AVR via J sternotomy (group B, N.=247) or full-sternotomy (group C, N.=174). RESULTS: Patients in group A were significantly older than groups B and C (77±5 vs. 74±7 and 70±8 years; P<0.001). Aortic cross-clamp and cardiopulmonary bypass times were shorter in group A than in groups B and C. As expected, aortic cross-clamp time was prolonged in group B as compared to groups A and C (60±18 vs. 36±10 and 54±16 min; P<0.001). After multivariate adjustment, minimally invasive AVR resulted in significantly fewer postoperative complications in terms of drainage bleeding and the need for blood transfusions (385±287 vs. 500±338 mL, P=0.006; and 1.3±2.1 vs. 1.8±2.6 IU, P=0.001, respectively). No differences in postoperative outcomes were observed among groups. CONCLUSIONS: The minimally invasive approach confers a protective effect against bleeding complications, but it is time-consuming. The use of sutureless valves is associated with significantly shorter surgical times compared with stented bioprostheses. In addition, no differences in mortality were observed among groups, and patients who received a sutureless valve, though significantly older, showed a better clinical outcome than patients who received a stented valve.

Current knowledge and future perspectives regarding stented valves.

Aortic valve bioprostheses are commonly implanted in the current era (also in younger patients) as they may obviate the need for anticoagulation while providing better hemodynamic performance and a more favorable quality of life. The steady increase in the use of biological valves has prompted the development of several different models of conventional stented bioprostheses. At present, there are four main types of stented aortic bioprostheses that compete in the market: the LivaNova Crown PRT (LivaNova Group, Burnaby, Canada), the St. Jude Medical Trifecta (St. Jude Medical, St. Paul, MN, USA), the Carpentier-Edwards Perimount Magna Ease (Edwards Lifesciences, Irvine, CA, USA), and the Medtronic Mosaic Ultra (Medtronic, Inc., Minneapolis, MN, USA). The purpose of this review is to describe the features of these bioprosthetic valve models and to compare the data provided by the manufacturers with those derived from the available literature.

What's up on stented valves.

Aortic valve bioprostheses are commonly implanted in the current era - also in younger patients - as they may obviate the need for anticoagulation while providing better hemodynamic performance and a more favorable quality of life. The steady increase in the use of biological valves has prompted the development of several different models of conventional stented bioprostheses. At present, there are four main types of stented aortic bioprostheses that compete in the market: the LivaNova Crown PRT (LivaNova Group, Burnaby, Canada), the St. Jude Medical Trifecta (St. Jude Medical, St. Paul, MN), the Carpentier-Edwards Perimount Magna Ease (Edwards Lifesciences, Irvine, CA), and the Medtronic Mosaic Ultra (Medtronic, Inc., Minneapolis, MN). The purpose of this review is to describe the features of these bioprosthetic valve models and to compare the data provided by the manufacturers with those derived from the available literature.

What's up on sutureless valves.

Sutureless aortic bioprostheses have been developed for use in high-risk patients undergoing surgical aortic valve replacement due to severe aortic stenosis. These devices are mounted on a stent and are self-anchoring within the aortic annulus with no need for sutures, resulting in shorter operative and, hence, ischemic times. The use of these devices makes therefore valve implantation easier and faster, which seems to improve postoperative outcomes. At present, there are two commercially available sutureless aortic valves: the Perceval S (LivaNova Group, Milan, Italy) and the Intuity (Edwards Lifesciences, Irvine, CA, USA). In this paper the studies published to date evaluating these two bioprosthesis models are reviewed, along with future directions and indications for the target patient population.

Evaluation of serum cysteine-rich protein 61 and cystatin C levels for assessment of acute kidney injury after cardiac surgery.

Objective The occurrence of acute kidney injury (AKI) after cardiopulmonary bypass (CPB) can lead to morbidity and mortality. We hypothesized that cysteine-rich protein 61 (CYR61) and cystatin C (CysC) may be potential novel biomarkers of AKI after cardiopulmonary bypass. Methods Patients were classified into AKI and non-AKI group depending on serum creatinine. Levels of creatinine, CysC, and CYR61 were measured at five time-points before and within 48 h after the surgery. Results Fifty patients were included in the study. Serum creatinine pre-operative values were 74.0 ± 43.3 µmol/L in AKI group vs. 64.8 ± 17.9 µmol/L in non-AKI group. During 48 h, the values increased to 124.6 ± 67.2 µmol/L in AKI group (p < 0.001) but in non-AKI group they did not change significantly. Serum CysC values were significantly increased already 2 h after CBP in AKI group (949 ± 557 µg/L, p < 0.05) compared to non-AKI group (700 ± 170 µg/L). Pre-operative serum CYR61 tended to be lower in AKI group (12.4 µg/L) than in non-AKI group (20.3 µg/L), but 24 h after the surgery, the levels in AKI group tended to be higher than non-AKI group. Conclusion Serum CYR61 does not seem to be an early predictor of AKI in patients after cardiac surgery with CPB, but it might possibly identify patients at risk of developing more severe kidney injury. Serum CysC could be a promising biomarker of AKI, differentiating patients at risk of developing AKI after cardiac surgery as early as 2 h after surgery.

Ventricular repolarization dynamicity and arrhythmic disturbances after beating-heart and arrested-heart revascularization.

BACKGROUND: Arrhythmias attributable to altered autonomic modulation of the heart, with elevated sympathetic and depressed vagal modulation, occur to a similar extent after surgery performed on beating or arrested hearts. Coronary artery bypass grafting (CABG) with cardiopulmonary bypass has been associated with more frequent occurrence of arrhythmic events than surgery performed without CABG, even with comparable levels of postoperative cardiac autonomic (dis) regulation after arrested- and beating-heart revascularization. We explored the effects of arrested- and beating-heart revascularization procedures on the dynamics of ventricular repolarization and on increased postoperative arrhythmic events. METHODS: Study participants included 57 CABG patients; 28 underwent on-pump and 29 underwent off-pump procedures. The 2 groups were comparable regarding clinical and postoperative characteristics. With high-quality 15-minute digital electrocardiograms, we assessed ventricular repolarization dynamics using RR and QT intervals and analyzed QT variability (QTV) and QT-RR interdependence. RR and QT intervals were determined from stationary 5-minute segments. QT-interval variability was determined by a T-wave template-matching algorithm. We used linear regression to compute the slope/correlation of the QT/RR interval. The Fisher exact test, nonpaired t-test, and ANOVA were applied to test the results; P <.05 was considered significant. RESULTS: Postoperative arrhythmic events were significantly more frequent in both groups. One week postoperatively these events were significantly more frequent in the on-pump group. In both groups, the RR interval was shorter after CABG (P <.001). The QT variability index increased from -1.2 + or - 0.6 to -0.8 + or - 0.4 after off-pump CABG and from -1.3 + or - 0.5 to -0.5 + or - 0.6 on day 4 after surgery (P <.05), further deteriorating to -0.2 + or - 0.6 one week after CABG in the on-pump group only (P <.05). QT-RR correlations decreased from 0.39 to 0.24 in the off-pump vs 0.34 to 0.17 in the on-pump group (P <.05), and in both groups they remained significantly reduced for as long as 4 weeks after CABG. CONCLUSIONS: For both on- and off-pump CABG, beat-to-beat heart-rate changes and rate-dependent ventricular repolarization adaptation showed disparities that worsened after surgery. The observed repolarization lability after CABG procedures seems to be transient but more pronounced after on-pump CABG. The association of arrhythmic events with ventricular repolarization lability changes in the setting of faster heart rates offers novel insights into the mechanisms of perioperative proarrhythmia after beating- and arrested-heart revascularization.

How does successful off-pump pulmonary vein isolation for paroxysmal atrial fibrillation influence heart rate variability and autonomic activity?

OBJECTIVE: : Surgical pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (PAF) blocks trigger stimulation from PVs and partially disconnects the atria from sympathetic and parasympathetic neural stimulation. This study describes long-term changes in heart rate variability (HRV) and autonomic activity (AA) after successful bipolar radiofrequency PVI. METHODS: : Twenty-seven patients who underwent coronary artery bypass grafting and successful (defined as stable sinus rhythm for 1 year) off-pump bipolar radiofrequency PVI for PAF were prospectively followed 3, 6, and 12 months after surgery including 24 hours Holter electrocardiogram. The following HRV and AA parameters were calculated: mean NN-interval, SD of NN-intervals, SD of averaged NN-intervals, root mean square of successive differences, low frequency (LF) power (0.04-0.15 Hz; a parameter specific for sympathetic activity), high frequency (HF) power (0.15-0.4 Hz; a parameter specific for parasympathetic activity), and the LF:HF ratio. RESULTS: : Preoperatively, high HRV and AA parameters were recorded. In 3-, 6-, and 12-month time, a progressive reduction of HRV and AA was observed, reaching significance after 12 months. Respective rates before surgery and 12 months after it were: for SD of averaged NN-intervals (122.4 ± 113; 80.5 ± 42 milliseconds; P = 0.046), for root mean square of successive differences (79.2 ± 93; 45 ± 20 milliseconds; P = 0.04). The LF:HF ratios were 1.22 and 0.73 before and 12 months after surgery, respectively. The statistically significant continuous reduction in LF:HF ratio (P = 0.02) is suggestive of a progressive parasympathetic dominance 12 months after surgery. CONCLUSIONS: : Successful PVI for PAF results in HRV and sympathetic activity reduction with preoperative sympathetic dominance and oncoming vagal dominance after 1 year from surgery. Despite preoperative sympathetic dominance, successful PVI for PAF results in HRV and a reduction in sympathetic activity with emerging parasympathetic dominance 12 months after surgery.

Effects of beating- versus arrested-heart revascularization on cardiac autonomic regulation and arrhythmias.

BACKGROUND: Altered autonomic regulation after cardiac operations precipitates cardiac arrhythmias, affects repolarization, and increases the risk of sudden cardiac death. We sought to clarify how the 2 different techniques of coronary artery bypass grafting (CABG), namely conventional CABG using cardiopulmonary bypass (on-pump) and beating-heart CABG without cardiopulmonary bypass (off-pump), affect cardiac autonomic regulation and arrhythmic disturbances postoperatively. METHODS: We included 57 consecutive patients, 28 in the on-pump group and 29 in the off-pump group. The electro-cardiographic recordings were performed on the preoperative day and the fourth, seventh, and twenty-eighth day after operation. Fifteen-minute digital recordings were taken; one channel was used to record electrocardiogram and the other breathing. Detailed analyses of arrhythmia, heart rate, and heart rate variability indices were performed on respective days to assess sympathetic and parasympathetic modulation of the heart and relate it to detected arrhythmic disturbances. RESULTS: Total power, low-frequency power, which indicates baroreceptor-mediated sympathetic modulation, and high-frequency power, indicating parasympathetic vagal modulation, declined significantly in both groups after CABG (P < .001); however, 7 days after CABG, total and high-frequency power were better preserved in the off-pump group. Mean RR interval was longer in the off-pump group at 7 (P= .006) and 28 days (P= .008) after surgery. The total incidence of arrhythmic events was higher in the on-pump group on the seventh day (P = .017, adjusted odds ratio = 8.6, 95% confidence interval 1.4-80.3). CONCLUSIONS: The results show profound impairment of cardiac autonomic regulation after CABG, showing better preserved cardiac autonomic modulation 7 days after beating-heart revascularization. Evidence suggests that slower restoration of heart rate and increased incidence of arrhythmic events after CABG using cardiopulmonary bypass are the result not only of impaired cardiac autonomic regulation but also of the involvement of additional factors of nonautonomic origin.

Assessment of cardiac autonomic regulation and ventricular repolarization after off-pump coronary artery bypass grafting.

BACKGROUND: Altered autonomic regulation precipitates cardiac arrhythmias and increases the risk of sudden cardiac death. This risk is further increased by changes in ventricular repolarization. Autonomic regulation is deranged in patients after myocardial on-pump revascularization. We aimed to clarify how off-pump coronary artery bypass grafting (CABG) affects postoperative cardiac autonomic regulation and ventricular repolarization within 4 weeks after CABG. METHODS: Forty-two patients (mean age, 61.9 +/- 9.3 years; mean EURO score 2.6 +/- 1.9) were electively admitted for off-pump CABG. The electrocardiographic and respiratory waveform recordings were performed in the afternoon in the supine position for 10 minutes. Autonomic modulation was assessed using heart rate variability analysis. Power spectra were computed from 5-minute stable RR intervals using Fourier Transform analysis. Total power of spectra was defined in the range of 0.01 to 0.40 Hz, high-frequency power within 0.15 to 0.40 Hz, and low-frequency power within 0.04 to 0.15 Hz. Normalized power was defined as a ratio of power in each band/total power. The high- and low-frequency power as well as their normalized values indicated cardiac vagal and sympathetic modulation, respectively. Ventricular repolarization was assessed using QT interval, QT interval variability, and QT-RR interdependence analysis. QT intervals were determined from the beginning of the 5-minute segments. QT interval variability was evaluated by a T-wave template-matching algorithm. Pearson correlation between length of RR and QT interval was applied to study QT-RR characteristics. The results were tested for significance using the Fisher exact test, nonpaired t test, and analysis of variance; a P <.05 was considered significant. RESULTS: The frequency of arrhythmic events and heart rate increased from the fourth to the seventh postoperative day and returned to preoperative levels 4 weeks after CABG. Heart rate variability measures indicating autonomic modulation remained depressed even 4 weeks after the procedure. QT variability index increased from -1.2 +/- 0.5 to -0.8 +/- 0.4 on the fourth day after the operation (P <.05) and returned to -1.0 +/- 0.5 4 weeks after CABG (P = not significant). QT-RR correlation decreased from 0.41 to 0.23 (P <.05) and remained significantly impaired as long as 4 weeks after CABG. CONCLUSIONS: Observed faster heart rates until 1 week after off-pump CABG imply excessive adrenergic activation, which is comparable to on-pump CABG procedure rates. The results indicate profound autonomic derangement and loss of rate-dependent regulation after off-pump CABG even 4 weeks after operation. Restituted repolarization as assessed by QT variability index 4 weeks postoperatively corresponded with decreased frequency of rhythm disturbances 4 weeks after CABG. The loss of coupling between QT and RR intervals shows increased electrical instability postoperatively, which may serve as an additional promoter for postoperative arrhythmias, especially at higher heart rates.