Sudden cardiac death after coronary artery bypass grafting is not predicted by signal-averaged ECG

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.

Implantable cardioverter-defibrillators improve survival after coronary artery bypass grafting in patients with severely impaired left ventricular function

Objective

Patients with severe left ventricular (LV) dysfunction have a poor long term survival despite complete surgical revascularization. Recent data suggests that the use of Implantable Cardioverter-Defibrillator (ICD) improves survival in patients with severe LV dysfunction. We compared the survival impact of ICD implantation in patients with severe LV dysfunction who underwent CABG.

Methods

Between January 1996 and August 2004, 305 patients with LV ejection fraction (EF) ≤25% had CABG surgery at our institution. Demographics of patients who had received an ICD (ICD+) in the post -operative period was compared to those without ICD (ICD-). Survival was evaluated by the Kaplan-Meier method.

Results

Of the entire group, 35 (11.5%) patients received an ICD with a median of 2 (+/-2) years after CABG. Indication for ICD implantation was clinical evidence of non sustained ventricular tachycardia (NSVT). There were no differences between the 2 groups with respect to age, gender, NYHA classification, number of bypasses, or other co-morbidities. Survival at 1, 3 and 5 years was 88%, 79%, and 67% for the ICD- group compared to 94%, 89% and 83% for the ICD+ group, respectively (figure, p < 0.05).

Conclusion

Implantation of ICD after CABG confers improved short and long term survival benefit to patients with severe LV dysfunction. Prophylactic ICD implantation in the setting of severe LV dysfunction and CABG surgery should be considered.

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.

Risk factors of ventricular tachyarrhythmias after coronary artery bypass grafting

BACKGROUND

Ventricular arrhythmias are rare and represent the most serious arrhythmic complication after coronary artery bypass grafting (CABG).

METHODS

The present retrospective study was conducted for identifying patients at risk of ventricular arrhythmias with ventricular signal averaged ECG, standard deviation of all normal RR intervals (SDNN), angiographic and echocardiographic data. We defined ventricular arrhythmias as sustained ventricular fibrillation and ventricular tachycardia. The study population consisted of 209 consecutive patients with sinus rhythm undergoing CABG. The primary endpoint was the occurrence of VA after CABG. The secondary endpoints were hospital length of stay after CABG and the occurrence of VA after hospital discharge.

RESULTS

During the postoperative follow-up ventricular arrhythmias were observed in 11 patients (5%). Patients with ventricular arrhythmias showed a higher incidence of ventricular late potentials (91 vs. 9% of patients, p<0.0001) than patients without ventricular arrhythmias. In addition patients with ventricular arrhythmias had a lower left ventricular ejection fraction (44.2+/-15.2 vs. 60.1+/-13.1%, p<0.0001) and a SDNN (22.4+/-8.8 vs. 34.4+/-16.1 ms, p<0.02). A stepwise logistic regression analysis of all variables identified the combination of ventricular late potentials, ejection fraction < or = 38% and SDNN < or = 28 ms (odds rate 26.00; 95% CI, 3.44-196.67, p<0.002) as an independent predictor of ventricular arrhythmias.

CONCLUSIONS

The results of our study suggest that the probability of ventricular arrhythmias could be predicted after CABG by a combination of low left ventricular ejection fraction and a measurement of ventricular signal averaged ECG and standard deviation of all normal RR intervals. Patients who can be identified as having a high risk of ventricular arrhythmias should be observed carefully after surgery.

High-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery

BACKGROUND

High-frequency QRS potentials are sensitive to myocardial ischemia. The aim of this study was to evaluate the usefulness of high-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery.

METHODS

Seventy patients undergoing coronary artery bypass grafting or heart valve surgery were involved. High-frequency QRS potentials were measured by signal-averaged electrocardiogram, and calculated as the root-mean-square voltage of the total QRS duration (RMST). The postoperative RMST was expressed as a percentage of the preoperative RMST. The mean RMST at 1 to 2 hours after removing the aortic cross-clamp was compared with the cardiac index, inotropic agents, and aortic cross-clamping time. The occurrence of ventricular tachycardia within 24 hours and the RMST at 2 postoperative days were also evaluated. Patients were divided into quartile groups from highest to lowest at postoperative RMST (groups 1, 2, 3, and 4, respectively, from maximum to minimum).

RESULTS

In postoperative states, cardiac index significantly decreased in accordance with the RMST decrease in a stepwise manner, although there were no differences in cardiac index among the four groups preoperatively. Inotropic agents and aortic cross-clamping time increased as RMST decreased. A high rate of ventricular tachycardia within 24 hours and delayed RMST recovery at 2 postoperative days were seen in group 4. The curve of sensitivity and specificity showed that severe reduction (threshold, 35%) of RMST indicated low-output syndrome.

CONCLUSIONS

The severe reduction of filtered high-frequency QRS potentials was related to myocardial dysfunction. Measurement of filtered high-frequency QRS potentials could become a useful, noninvasive, real-time monitor of myocardial dysfunction after surgery.

Impact of diabetes mellitus on the improvement in signal-averaged electrocardiography after coronary artery bypass grafting

BACKGROUND

Although it has been reported that coronary artery bypass grafting (CABG) for multivessel disease markedly improves several parameters of signal-averaged electrocardiography (SAECG), its beneficial effect on SAECG is variable. The hypothesis of the present study was that the presence of diabetes mellitus (DM) affects the improvement in SAECG after CABG.

METHODS AND RESULTS

Pre- and post-operative SAECGs were recorded in 100 consecutive patients who underwent complete surgical revascularization. Changes in the following parameters were compared between the diabetic (n=43) and non-diabetic (n=57) patients: filtered QRS duration (dQRS), root mean square voltage in the terminal 40 s of the QRS complex (RMS40), and duration of the terminal low-amplitude signal lower than 40 microV (LAS40). Although baseline characteristics and the occurrence of late potentials were similar in both groups, quantitative improvements in the SAECG parameters after CABG were significantly greater in non-diabetic than in diabetic patients (dQRS: 109 +/- 22 ms vs 102 +/- 19 ms in diabetics and 106 +/- 21 ms vs 88 +/- 11 ms in non-diabetics; p=0.028, RMS40: 55 +/- 46 microV vs 65 +/- 38 microV in diabetics and 50 +/- 37 microV vs 76 +/- 37 microV in non-diabetics; p=0.037, LAS40: 31 +/- 20 ms vs 26 +/- 17 ms in diabetics and 32 +/- 12 ms vs 17 +/- 8 ms in non-diabetics; p=0.007, respectively).

CONCLUSIONS

The presence of DM limits the CABG-induced improvement in SAECG. In diabetic patients, therefore, perioperative changes of the SAECG must be interpreted with caution.

Quantitative improvement in signal-averaged electrocardiography after coronary artery bypass grafting

Abnormal signal-averaged electrocardiography (SAECG) reflects slow and heterogeneous myocardial conduction, predicting ventricular arrhythmia and sudden cardiac death in patients with ischemic heart disease. The purpose of this study was to investigate the quantitative effect of coronary artery bypass grafting (CABG) on SAECG, which is still controversial, and to identify the factors that are related to it. Pre- and postoperative SAECGs were recorded in 100 patients who underwent CABG. Compared parameters included filtered QRS duration (dQRS), root mean square voltage in the terminal 40 ms of the QRS complex (RMS40), and duration of the terminal low-amplitude signal less than 40 microV (LAS40). All 3 parameters in SAECG improved significantly after CABG (dQRS: 105+/-21 ms-->99+/-18 ms, RMS40: 55+/-45 microV-->65+/-41 microV, LAS40: 29+/-19 ms-->25+/-12 ms). The improvements in SAECG were greater in patients who underwent complete revascularization and in those without prior myocardial infarction. In conclusion, CABG improved SAECG quantitatively, even in patients with normal SAECG. However, this improving effect was variable and closely related to the presence of prior myocardial infarction and the completeness of revascularization.