Evaluation of aortocoronary venous bypass grafting for prevention of cardiac arrhythmias

The effect of myocardial surgical revascularization on left ventricular late potentials

BACKGROUND

The presence of ventricular late potentials (LP) is an important indicator for the development of ventricular tachyarrhythmias due to ischemic heart disease. The effect of myocardial revascularization on LP has remained controversial. The purpose of this study was to determine whether complete myocardial surgical revascularization (CABG) documented by myocardial perfusion scintigraphy might alter the substrate responsible for LP.

METHODS

Prospectively, enrolled patients undergoing elective CABG were evaluated with thallium-201 myocardial perfusion scintigraphy and signal- averaged ECG pre- and postoperatively. SAECG recordings were obtained serially: before, 48-72 hours and 3 months after CABG. LPS were defined as positive if SAECG met at least two of Gomes criteria. Scintigraphies were performed pre- and 3 months postoperatively for determination of the success of revascularization. Changes observed in SAECG recordings after CABG were compared between those with and without successful revascularization.

RESULTS

CABG resulted in successful revascularization in 23 patients and was unsuccessful in 17 (no change or deterioration of the perfusion defects). Preoperative SAECG values were not different between groups except for RMS values. The incidence of LP decreased significantly postoperatively in patients with improved myocardial perfusion, whereas there were no changes in patients who did not have postoperative perfusion improvement (McNemar test, P < 0.05).

CONCLUSIONS

LPs disappear following the elimination of myocardial ischemia by complete surgical revascularization. Persistence of ischemia following CABG usually results in the persistence of late potentials. The incidence of ventricular arrhythmias is expected to be unchanged in these patients and they should be reevaluated for reinterventions.

Ventricular arrhythmia following successful myocardial revascularization: incidence, predictors and prevention

OBJECTIVES

We estimated the risk of sudden cardiac death (SCD), from a spontaneous episode of ventricular arrhythmia (VT/VF), after a successful surgical myocardial revascularization (coronary artery bypass grafting; CABG) procedure. Predictors of these events were identified, and long term benefits of the prophylactic regimes, that were used to control these events, were evaluated.

METHODS

We selected 8642 consecutive patients, who had undergone an isolated and first time CABG procedure, between 1/3/1980 and 1/3/1995. A standard hazard function model (1) was used for statistical analysis. Efficacy of the prophylactic regimes, was examined in a group of 350 high risk patients, with a preoperative left ventricular ejection fraction 30% or less, who were recently operated since 1/1/1988. Electrophysiologic (EP) guided prophylaxis was used in 92 (26%) patients, who had survived a documented episode of SCD, and remaining 258 patients were maintained on antiarrhythmic medication on an empirical basis. A sequential EP evaluation was performed, when indicated.

RESULTS

During an early phase of hazard, which mainly lasted for up to 3 months after CABG, incremental risk factors were preoperative LVEF 30% or less (P = 0.0007) and preoperative episodes of VT/VF (P = 0.04). This phase was followed by a constant phase with a low risk of the events, which merged into a slowly rising late phase after 6 years. EP guided prophylaxis, reduced the risk of SCD in high risk patients (P = 0.03). A sequential EP evaluation, helped to detect the problems of drug resistance and a cross over from non-sustained to sustained runs of VT/VF.

CONCLUSIONS

Despite a successful CABG surgery, risk of VT/VF persists. A routine EP evaluation before and after a CABG procedure is recommended in all patients with a poor left ventricular function.

Prognosis of patients with frequent premature ventricular complexes and nonsustained ventricular tachycardia after coronary artery bypass graft surgery

BACKGROUND

Previous studies in small groups of predominantly nongeriatric patients showed that complex ventricular arrhythmias occurring after coronary artery graft (CABG) surgery are of no prognostic significance. The purpose of this study was to compare the prognosis of patients with and without advanced grade ventricular arrhythmias (AGVA) after CABG in a large group of patients. [In this paper, AGVA is used as an abridged definition of frequent premature ventricular complexes (PVCs) and nonsustained ventricular tachycardia (NSVT) which represent advanced grade ventricular arrhythmias.]

METHODS

Twenty-four hour ambulatory electrocardiographic (ECG) monitoring was performed 3 days after CABG in 185 consecutive patients with 185 closely matched control patients without AGVA. Of 185 patients with AGVA, 77 had frequent PVCs, 45 had NSVT, and 63 patients had both. The average age of both groups was 65 +/ 9.7 years. Patients were followed for 34 +/ 10 months, and in 30 patients ambulatory monitoring was repeated at the end of the follow-up.

RESULTS

Fifteen AGVA and nine control patients died. In each group seven deaths were noncardiac. Six nonsudden and two sudden cardiac deaths (SCD) occurred in the AGVA group at 2-36 months after CABG and two nonsudden cardiac deaths in the control group at 3 and 35 months after CABG (p = 0.053). Both SCDs occurred 33 months after CABG after new events known to predispose to SCD. In 18 of 30 patients AGVA was no longer present when ambulatory ECG monitoring was repeated 36 +/ 11 months after CABG.

CONCLUSION

AGVA after CABG was not a marker of an early sudden cardiac death. In 60% of patients not treated with antiarrhythmic drugs, AGVA was no longer present late after operation.

Usefulness of late potentials on the immediate postoperative signal-averaged electrocardiogram in predicting ventricular tachyarrhythmias early after isolated coronary artery bypass grafting

The present study was undertaken to determine the value of abnormal late ventricular potentials on signal-averaged electrocardiograms (ECG) in identifying patients at risk of developing ventricular tachycardia or ventricular fibrillation in the early postoperative period after coronary artery bypass grafting. Signal-averaged ECGs were recorded immediately after operation in 72 patients. Abnormal late potentials were defined as the presence of 2 or 3 of the following: (1) root-mean-square amplitude of the last 40 ms of the QRS < 20 microV; (2) duration of the terminal QRS potentials (after 40 microV) > or = 39 ms; and (3) high-frequency QRS duration > 120 ms (in patients with conduction defects, only the first 2 criteria were used). Abnormal late ventricular potentials were present on the immediate postoperative signal-averaged ECG in 26 of the 72 patients (36%). Life-threatening ventricular tachyarrhythmias occurred in 6 patients. Late potentials were present in all 6 patients, but only in 20 of 66 (30%) who did not develop ventricular tachyarrhythmias (p < 0.005) (sensitivity 100%, specificity 70%, predictive accuracy 72%). Of 12 pre- and perioperative variables examined by univariate and multivariate regression analysis, the presence of late potentials on the signal-averaged ECG and low cardiac output postoperatively were found to be independent predictors of life-threatening tachyarrhythmias.

Contraindications to vasoconstrictors in dentistry: Part I. Cardiovascular diseases

This article reviews the main contraindications of vasoconstrictors in cardiac patients, notably unstable angina, recent myocardial infarction, recent coronary artery bypass surgery, refractory arrhythmias, untreated or uncontrolled hypertension, and untreated or uncontrolled congestive heart failure. Extensive survey of the literature has been completed, giving specific guidelines for a rational use of vasoconstrictors in this category of medically compromised patients.

Prevalence and prognostic significance of exercise-induced ventricular arrhythmias after coronary artery bypass grafting

Exercise-induced ventricular arrhythmias occur often after coronary artery bypass grafting (CABG), but their prognostic significance is unknown. Two hundred patients examined by exercise electrocardiography and cardiac catheterization (including left ventriculography, bypass graft and native coronary artery angiography) before and 3 months after CABG were prospectively followed up. Exercise-induced ventricular arrhythmias occurred more often after (49 of 200 patients, 24.5%) than before (32 of 200 patients, 16.0%) CABG (p less than 0.05). There were no differences between the patients with and without ventricular arrhythmias in the prevalence of graft patency (79 vs 80%) or the postoperative ejection fraction (57 +/- 9 vs 57 +/- 12%). Ten cardiac deaths occurred during the mean follow-up time of 61 +/- 19 months, 8 of which were witnessed sudden cardiac deaths. All cardiac deaths occurred in patients who did not have exercise-induced ventricular arrhythmias after CABG. The postoperative ejection fraction was lower in the cardiac death patients (42 +/- 16%) than in the survivors (58 +/- 10%) (p less than 0.01). No other clinical or angiographic variable predicted the occurrence of cardiac death. Thus, the prevalence of exercise-induced ventricular arrhythmias increases after CABG, but the occurrence of ventricular arrhythmias does not indicate an increased risk of cardiac death.

Prevalence and prognostic significance of complex ventricular arrhythmias after coronary arterial bypass graft surgery

To assess the prevalence and long-term prognostic significance of complex ventricular arrhythmias after coronary arterial bypass graft surgery, 126 patients were studied by 24-hour ambulatory electrocardiographic recordings and cardiac catheterizations (including left ventricular, coronary arterial and bypass graft angiograms) before and 3 months after surgery, and then prospectively followed-up for a mean of 50 months. Complex ventricular arrhythmias (ventricular premature complexes greater than 30/hour, multiform and/or repetitive complexes) occurred more commonly after than before surgery (in 49/126 vs. 30/126 patients, P less than 0.05). In 18 patients (14%) who had significant worsening of ventricular arrhythmias, the ejection fraction decreased significantly (from 56 +/- 13% to 50 +/- 15%, P less than 0.05) after operation. During the period of follow-up, there were 4 witnessed sudden cardiac deaths. Complex ventricular arrhythmias tended to be more prevalent in patients who died suddenly (in 100%) compared to survivors (in 37%), but their presence did not predict the subsequent sudden death when ejection fraction was included in the stepwise regression model. None of the patients with an ejection fraction over 40% suffered sudden death despite the prevalence of complex arrhythmias in 32% of these patients. Thus, complex ventricular arrhythmias tend to occur more frequently after than before bypass surgery and their occurrence appears to be related to impairment of left ventricular function. Patients with well preserved ventricular function are at low risk of dying suddenly despite presence of complex ventricular arrhythmias after surgery.

Short-term effect of coronary artery bypass grafting on the signal-averaged electrocardiogram

Ventricular late potentials at the end of the QRS can be detected on the body surface during sinus rhythm by recording a signal-averaged electrocardiogram (SAECG). In patients with coronary artery disease, these late potentials have been shown to be markers for spontaneous or inducible ventricular tachycardia, or both. The short-term (before and 10 +/- 4 days after coronary revascularization) influence of coronary artery bypass grafting (CABG) on the quantitative SAECG variables was studied in 40 patients with chronic coronary artery disease. Twenty-five of these patients had a previous myocardial infarction. In the 15 patients without previous myocardial infarction, no abnormal SAECG indexes were recorded before CABG and no change in the quantitative SAECG variables was observed after surgery. In the patients with a previous myocardial infarction, 7 (28%) had a late potential before CABG. After CABG, 5 (71%) patients remained late potential-positive, whereas the other 2 (29%) lost their late potential. The mean values of their SAECG variables improved after coronary revascularization. In the entire group of postmyocardial infarction patients, the high-frequency QRS duration had shortened (p less than 0.01) after CABG (the other SAECG indexes did not change). The postoperative arrhythmic complications (transient atrial fibrillation, new onset of ventricular couplets) tended to be more frequent in the postmyocardial infarction group and in patients with late potentials. Our findings suggest that the reported increase in ventricular arrhythmias after CABG is probably not related to a change in the arrhythmogenic substrate for ventricular reentry but is associated with changes in the arrhythmogenic milieu.

De novo refractory ventricular tachyarrhythmias after coronary revascularization

Twelve of 1,675 patients who underwent coronary artery bypass grafting during a 2.5-year period had new onset, recurrent, sustained ventricular tachyarrhythmia a mean of 27 days (range 2 to 150) postoperatively. No patient had an intra- or perioperative myocardial infarction and all patients were hemodynamically stable and had normal metabolic and electrolytic indexes at the time of ventricular tachyarrhythmia. Preoperative ejection fraction was 39 +/- 10% (mean +/- standard deviation) and all patients had Lown grade II or less ventricular ectopic activity on ambulatory monitoring. Postoperative angiography demonstrated occluded saphenous vein grafts in 3 of 7 patients studied, none of whom had symptoms suggestive of myocardial ischemia. Treatment with conventional antiarrhythmic therapy was unsuccessful in all but 1 patient, and 10 patients were treated with amiodarone and 1 patient with propafenone. Four of these patients also received an automatic implantable defibrillator. Thus, de novo ventricular tachyarrhythmia can occur unexpectedly after coronary artery bypass grafting and may be the result of several factors related to either subclinical graft occlusion or increased dispersion of repolarization secondary to reperfusion.

Ventricular arrhythmias after coronary artery bypass graft surgery: incidence, risk factors and long-term prognosis

The incidence, risk factors and long-term prognosis of complex ventricular arrhythmias after coronary artery bypass graft surgery are not known. Complex ventricular arrhythmias are defined as Lown grades 4a (couplets), 4b (ventricular tachycardia) and 5 (R on T phenomenon). Ninety-two patients with normal left ventricular function who underwent elective coronary artery bypass graft surgery were prospectively evaluated. Ventricular arrhythmias were documented by predischarge 24 hour ambulatory electrocardiographic monitoring; 43% of patients had no or simple ventricular arrhythmias (Lown grades 1 to 3) and 57% had complex ventricular arrhythmias. Risk factors analyzed included age, sex, diabetes, hypertension, smoking, preoperative digoxin or propranolol therapy, cardiopulmonary bypass time, aortic cross-clamp time, number of vessels bypassed, peak creatine kinase (CK) elevation and pericarditis. No risk factor identified patients at higher risk for complex ventricular arrhythmias. Patients were followed up for 6 to 24 months (mean 16). Patients with complex ventricular arrhythmias did not have a higher incidence of sudden death, cardiac death, syncope, angina, myocardial infarction or cerebrovascular accident. It was concluded that: Complex ventricular arrhythmias are common after coronary artery bypass graft surgery. None of the risk factors considered identify high risk patients. Complex ventricular arrhythmias after coronary artery bypass graft surgery do not indicate a poor prognosis in patients with normal left ventricular function.

When is myocardial mapping clinically valuable?

All cardiac arrhythmias are either automatic or reentrant. Automatic arrhythmias occur in the periinfarction or perioperative period. Chronic, recurrent arrhythmias are typically reentrant. By definition, reentrant arrhythmias are inducible with programmed electrical stimulation. When a malignant cardiac arrhythmia is identified, the patient is taken to the electrophysiologic laboratory for study. Reentrant ventricular tachyarrhythmias are induced with programmed electrical stimulation. Pharmacologic suppression is guided by electrophysiologic testing. When antiarrhythmic suppression fails, surgical intervention may be an effective alternative. Endocardial catheter mapping before surgery may serve as an important guide to the surgeon. Myocardial mapping is clinically valuable only when all antiarrhythmic therapy has failed, and the patient is considered to be a candidate for surgical intervention. When surgical intervention is planned, we consider preoperative catheter mapping desirable and intraoperative electrophysiologic localization mandatory.

Electrophysiologic studies before and after myocardial revascularization in patients with life-threatening ventricular arrhythmias

Electrophysiologic studies with programmed cardiac stimulation were performed in a selected group of 17 patients with severe proximal coronary artery disease involving at least 2 major vessels and left ventricular ejection fractions greater than 30% who were undergoing coronary artery bypass graft surgery after prehospital cardiac arrest or ventricular tachycardia (VT) unassociated with acute myocardial infarction. Before surgery and without antiarrhythmic drug therapy, programmed cardiac stimulation induced ventricular fibrillation (VF) in 4 patients, and VT (greater than or equal to 5 beats) in 11 patients. Inducible VT or VF was suppressed by antiarrhythmic drugs in 7 of 13 patients in whom they were tried. Patients underwent coronary artery bypass graft surgery unassociated with perioperative myocardial infarction. When studied again an average of 19 days after surgery, 10 patients had no inducible VT or VF without antiarrhythmic drug therapy; 6 had induced VT. One patient had spontaneous VT. An effective antiarrhythmic regimen that suppressed inducible or spontaneous VT, or both, was defined by serial electrophysiologic studies in 4 patients, whereas 3 patients continued to manifest electrically inducible VT with all antiarrhythmic regimens tested. All but 1 patient, in whom postoperative VT could not be suppressed, are free of arrhythmias after a mean follow-up period of 23 months (range 6 to 53). It is concluded that myocardial revascularization alone may improve the abnormal electrophysiologic findings in certain patients; however, this effect of coronary artery bypass graft surgery is unpredictable, and pre- and postoperative electrophysiologic studies are recommended as part of the evaluation of these patients.

Ventricular arrhythmia before and after aorto-coronary bypass surgery

The influence of aorto-coronary bypass surgery (ACBS) on ventricular arrhythmia was examined in 57 patients. Six-hour Holter monitoring was done on the day prior to and 3 mth after ACBS. None of the patients were on any antiarrhythmic drugs during these recordings. Ventricular arrhythmia was classified into three groups: Group I (45 patients) had an average of less than 10 premature ventricular contractions (PVCs) per hour, Group II (7 patients), 11-30 PVCs per hour and Group III (5 patients), greater than 30 PVCs per hour. There was no significant change in the number of patients in each group after ACBS. Complex PVCs were present in 8 patients preoperatively and in 9 patients after ACBS. The number of diseased vessels and the extent of left ventricular wall motion abnormality noted preoperatively, had no effect on ventricular arrhythmia following surgery. These data show that ACBS, when performed to relieve angina, does not have a significant effect on the prevalence of PVCs and does not prevent or reduce the occurrence of complex PVCs.