The effects of inflammation on heart rate and rhythm in a canine model of cardiac surgery.

BACKGROUND: Heart rate (HR) and rhythm disturbances are common after cardiac surgery. This study tests the hypothesis that the inflammation caused by cardiac surgery is an underlying mechanism for postoperative changes in HR, rhythm, and HR variability (HRV). METHOD AND RESULTS: Normal canines (n = 6 per group) were divided into 4 groups: (1) anesthesia, (2) sternotomy and pericardiotomy, (3) atriotomy, and (4) corticosteroids combined with an atriotomy. Continuous electrocardiographic recordings were done preoperatively and for 3 postoperative days. Electrophysiologic testing was done at the initial and terminal surgeries. C-reactive protein level was assessed at each study day, and tissue myeloperoxidase activity was assessed at the terminal study. Measurements of HRV were determined daily to detect changes in autonomic tone. Postoperatively, the HR increased in the pericardiotomy (P = .0005) and atriotomy (P = .001) groups and HRV decreased in both the groups. No significant change occurred in either the HR or HRV in the anesthesia (P = .52) and steroid (P = .16) groups. HRV (triangular index) on postoperative day 3 was correlated with the tissue myeloperoxidase levels (r = -.83; P = .0004). Autonomic blockade with atropine and esmolol resulted in an HR and HRV that were not significantly different between groups. Atrial premature beats occurred postoperatively in the all the groups except the anesthesia group and were independent of the degree of inflammation. CONCLUSION: Cardiac surgery increases the postoperative HR by reducing HRV, mostly because of a reduction in vagal tone. Furthermore, the magnitude of these changes is dependent on the degree of inflammation and is normalized by corticosteroids.

Diagnosis of multiple infarcts from complex electrocardiograms during normal rhythm, left bundle-branch block, and ventricular pacing.

INTRODUCTION: Because of better treatment of chronic coronary artery disease, patients with multiple ischemic insults are living longer and requiring long-term management. Electrocardiograms (ECGs) in patients with multiple myocardial infarctions (MMIs) are a challenge to the clinician or cardiologist. This is because second myocardial infarctions (MIs) often modify or obscure the ECG effects of the first MI and vice versa. This can result in complex tracings, which are difficult to interpret and predict the locations of damaged regions. It is important to identify MMI because, additively, they can result in poor ventricular function. METHODS: New criteria for the diagnosis of MMI were derived from studies in which ECGs and body surface potential distribution maps were correlated with epicardial and intramural depolarization in animal studies of MI and in patients at the time of coronary artery bypass graft and with the pathologic anatomy in a few patients. The initial criteria were fine tuned by correlations between ECGs and independent data obtained from catheterization and other imaging modalities (ultrasound and radionuclide single photon emission computed tomography). RESULTS: Often 2 or more MIs are concealed according to classical Q- and R-wave criteria. Myocardial infarctions located in opposing walls (180°), that is, inferior-superior, anterior-posterior, are the most difficult to identify. Two MIs that are not opposing (90°) are usually readily detectable. The pathologic Q waves produced by each separate MI, when opposing, are replaced by multiple QRS deflections or baseline crossings, which are referred to as M and W complexes. These waveforms replace Q waves and are equally weighted in a scoring system to improve diagnostic accuracy of ECG interpretation. These new criteria can also be used to predict MIs in left bundle-branch block, intraventricular conduction delay, and ventricular pacing. CONCLUSION: Multiple myocardial infarctions modify the ECG because they eliminate Q waves and result in confusing, splintered QRS waveforms, referred to as M and W complexes. New criteria are presented to diagnose the presence and locations of these MMIs, which predict reduced left ventricular function, in normal sinus rhythm, left bundle-branch block, and ventricular pacing.

Atrial fibrillation propagates through gaps in ablation lines: implications for ablative treatment of atrial fibrillation.

BACKGROUND: It has been hypothesized that atrial lesions must be transmural to successfully cure atrial fibrillation (AF). However, ablation lines often do not extend completely across the atrial wall. OBJECTIVE: The purpose of this study was to determine the effect of residual gaps on conduction properties of atrial tissue. METHODS: Canine right atria (n = 13) were isolated, perfused, and mounted on a 250-lead electrode plaque. The atria were divided with a bipolar radiofrequency ablation clamp, leaving a gap that was progressively narrowed. Conduction velocities at varying pacing rates and AF frequencies were measured before and after ablations. AF was induced with an extra stimulus and acetylcholine. RESULTS: Gap widths from 11.2 to 1.1 mm were examined. Conduction velocities through gaps were dependent cycle length (P = .002) and gap size (P <.001). Overall, 253 (97%) of a total of 260 gaps allowed paced propagation; 51 (91%) of 56 gaps 1-3 mm in width permitted paced propagation, as did 202 (99%) of 204 gaps >or=3.0 mm. Similarly, 253 (97%) of a total of 260 gaps allowed propagation of AF. For AF, 51 (93%) of 55 gaps 1-3 mm allowed AF to pass through, as did 202 (99%) of 205 gaps >or=3.0 mm. Gaps as small as 1.1 mm conducted paced and AF impulses. CONCLUSIONS: Conduction velocities were slowed through residual gaps. However, propagation of wave fronts during pacing and AF occurred through the majority of residual gaps, down to sizes as small as 1.1 mm. Leaving viable tissue in ablation lines for the treatment of AF could account for failures.

Pulmonary vein isolation and the Cox maze procedure only partially denervate the atrium.

OBJECTIVES: The effects of ablation lines on myocardial innervation and response to autonomic stimuli are unclear. This study examined the effects of radiofrequency ablation on atrial autonomic innervation and compared pulmonary vein isolation and the biatrial Cox maze procedure. METHODS: In 12 acute canines right and left vagosympathetic trunks and right and left stellate ganglia were isolated. Each nerve was stimulated before bipolar ablation, after pulmonary vein isolation, and after the Cox maze procedure. Nadolol (n = 6) and atropine (n = 6) were administered to block sympathetic and parasympathetic responses, respectively. Changes in heart rate and atrioventricular interval were compared. Changes in QRST area relative to an isoelectric baseline (index of local innervation) were calculated. RESULTS: Sympathetic stimulation of each nerve and parasympathetic stimulation of the vagosympathetic trunks caused significant changes in heart rate and atrioventricular interval. After pulmonary vein isolation, the effect of 33% of the nerves on heart rate changes was eliminated. The Cox maze procedure eliminated right stellate sympathetic effects on heart rate. Fifty percent of the nerves caused heart rate changes after the Cox maze procedure. There was no significant effect of either lesion set on atrioventricular interval changes. Stimulation of 50% of nerves after pulmonary vein isolation produced local area changes significantly different from control area. After the Cox maze procedure, a different 50% of the nerves produced local changes different from those seen after pulmonary vein isolation. CONCLUSIONS: Surgical ablation procedures disrupted innervation, affecting heart rate but not atrioventricular interval. Autonomic innervation affecting the atria was changed by pulmonary vein isolation and additionally by the Cox maze procedure. Residual autonomic effects were present even after the complete Cox maze procedure.

The early repolarization variant--an electrocardiographic enigma with both QRS and J-STT anomalies.

A detailed description of the electrocardiogram of the early repolarization variant, including its most common morphological variations is presented. Included is a recently identified anomaly of the QRS complex, which has not previously been reported. Ventricular activation data is presented to explain the unique QRS changes. A comparison with Wolff-Parkinson-White (preexcitation) reveals certain similarities related to a premature completion of depolarization in early repolarization variant.

The early repolarization variant--normal or a marker of heart disease in certain subjects.

The theory is advanced that the early repolarization variant may not always be benign and that it can become a substrate for ventricular arrhythmias, sudden death, and hypercontractility cardiomyopathy in some subjects, including certain high-performance athletes. In addition, it is suggested that it likely represents part of a spectrum of cardiovascular anomalies related to nonischemic ST elevation including Brugada syndrome, and that it may also have a molecular genetic origin of variable penetrance.

Spatial and temporal stability of the dominant frequency of activation in human atrial fibrillation.

PURPOSE: Intraoperative activation sequence mapping during atrial fibrillation (AF) is difficult because of the complexity of the data. The data analysis is time consuming, and picking activation times can be ambiguous. The purpose of this study was to determine whether mapping in the frequency domain during AF can be used to rapidly locate the region and assess the stability of the dominant frequency. METHODS: In 33 patients, epicardial bipolar electrograms were intraoperatively recorded from 250 sites during AF. For each electrogram, a power spectrum was calculated using a fast Fourier transform. The peak frequency below 11 Hz was determined from the power spectrum for each electrogram. RESULTS: Isofrequency mapping demonstrated that 91% of the patients exhibited a distinct region of maximum (dominant) frequency at least once during the recording period. Nine percent had no distinct region of dominant frequency. A distinct region of stable dominant frequency was located in the left atrium 30% of the time and the right atrium 12% of the time for the entire recording period. The location of dominant frequency changed during the recording period in 48% of the patients. The dominant frequency was highest in patients with chronic AF (8.29 +/- 1.0 Hz) compared to those with paroxysmal AF (PAF) (6.54 +/- 0.62 Hz, P = .001). The dispersion of frequency was higher in the patients with persistent AF (1.03 +/- 0.4 Hz) than in those with PAF (0.6 +/- 0.3 Hz, P < .001). CONCLUSION: Frequency mapping rapidly and accurately identifies the region of dominant activation frequency. The frequency is faster and more variable in persistent AF than in PAF. The location of the dominant frequency was unstable, changing during the recording period, in half the patients. The location of the dominant frequency was independent of the type of AF.

Left ventricular muscle band (VMB): thoughts on its physiologic and clinical implications.

Although the ventricular muscle band (VMB) is formed by one continuous band of myocardium and there is some evidence to suggest that it may contract sequentially along its course from the right ventricle, through the septum, then along its basoapical left ventricular spiral, the structure is not activated in this sequence. Activation as programmed by the fully developed Purkinje system proceeds broadly and directly from endocardium to epicardium and from apex to base. Although not activated sequentially along its course, the band may still contract and relax sequentially if there is a progressive lengthening of the contraction duration in association with a nonuniform lengthening of the cardiac fiber action potential (repolarization) duration. Also, the systolic and diastolic functions of the band should be considered as part of a complex, integrated electromechanical system in which the activation is programmed to ensure optimal function.

Importance of geometry and refractory period in sustaining atrial fibrillation: testing the critical mass hypothesis.

BACKGROUND: The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914. There has never been a systematic investigation defining the relationship between tissue geometry and AF. The purpose of this study was to determine the association among the probability of maintaining AF and the width, area, weight, effective refractory period (ERP), and wavelength in atrial tissue. METHODS AND RESULTS: Isolated canine atria (n=20) were perfused with Krebs-Henseleit solution. Baseline ERPs were obtained with and without acetylcholine (10E-3.5 mol/L) using single extra-stimulus pacing while unipolar electrograms were recorded from 250 sites. The tissue was then partitioned using bipolar radiofrequency ablation, and the ERPs were measured again with and without acetylcholine. Any section of tissue that maintained AF was divided until the arrhythmia was no longer inducible. ERPs and conduction velocities were measured in all of the sections after each ablation, and the wavelengths were calculated. The probability of AF was found to be correlated with increasing tissue areas, widths, and weights (P<0.001). The probability of AF was significantly associated with the length of the ERP and the wavelength (P<0.001). With shorter ERPs and shorter wavelengths, there was an increased probability of sustained AF. CONCLUSIONS: The probability of sustained AF was significantly associated with increasing tissue area, width, and weight and decreasing ERPs and wavelengths. These data may lead to a better understanding of the mechanism of AF and, thus, help to design more-effective interventional procedures in the future.

Inflammation of atrium after cardiac surgery is associated with inhomogeneity of atrial conduction and atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is common after cardiac surgery. Abnormal conduction is an important substrate for AF. We hypothesized that atrial inflammation alters atrial conduction properties. METHODS AND RESULTS: Normal mongrel canines (n=24) were divided into 4 groups consisting of anesthesia alone (control group); pericardiotomy (pericardiotomy group); lateral right atriotomy (atriotomy group); and lateral right atriotomy with antiinflammatory therapy (methylprednisolone 2 mg/kg per day) (antiinflammatory group). Right atrial activation was examined 3 days after surgery. Inhomogeneity of conduction was quantified by the variation of maximum local activation phase difference. To initiate AF, burst pacing was performed. Myeloperoxidase activity and neutrophil cell infiltration in the atrial myocardium were measured to quantify the degree of inflammation. The inhomogeneity of atrial conduction of the atriotomy and pericardiotomy groups was higher than that of the control group (2.02+/-0.10, 1.51+/-0.03 versus 0.96+/-0.08, respectively; P<0.005). Antiinflammatory therapy decreased the inhomogeneity of atrial conduction after atriotomy (1.16+/-0.10; P<0.001). AF duration was longer in the atriotomy and pericardiotomy groups than in the control and antiinflammatory groups (P=0.012). There also were significant differences in myeloperoxidase activity between the atriotomy and pericardiotomy groups and the control group (0.72+/-0.09, 0.41+/-0.08 versus 0.18+/-0.03 DeltaOD/min per milligram protein, respectively; P<0.001). Myeloperoxidase activity of the antiinflammatory group was lower than that of the atriotomy group (0.17+/-0.02; P<0.001). Inhomogeneity of conduction correlated with myeloperoxidase activity (r=0.851, P<0.001). CONCLUSIONS: The degree of atrial inflammation was associated with a proportional increase in the inhomogeneity of atrial conduction and AF duration. This may be a factor in the pathogenesis of early postoperative AF. Antiinflammatory therapy has the potential to decrease the incidence of AF after cardiac surgery.

Surgical treatment of atrial fibrillation: predictors of late recurrence.

OBJECTIVE: The Cox maze procedure was introduced in 1987 for the treatment of atrial fibrillation. This study evaluated the predictors of late atrial fibrillation recurrence in 276 consecutive patients who underwent this procedure at our institution. METHODS: From 1987 through June 2003, 276 patients (79 female and 197 male patients; mean age, 55 +/- 11 years) underwent the Cox maze procedure. Thirty-three patients had Cox maze procedure I, 16 patients had Cox maze procedure II, and 197 patients had Cox maze procedure III. The last 30 patients underwent a modified procedure (Cox maze procedure IV) with bipolar radiofrequency ablation. There were 113 (41%) patients who had a concomitant operation, most commonly either a mitral valve procedure (19%) or coronary artery bypass grafting (20%). Data were analyzed by means of univariate analysis, with preoperative and perioperative variables used as covariates. Patient follow-up was conducted by means of questionnaire, physician examination, and electrocardiographic documentation. All patients had a minimum of 6 months of follow-up. RESULTS: Patient follow-up was achieved in 92.8% of cases, with a mean follow-up time of 5.8 +/- 3.6 years. Risk factors for late atrial fibrillation recurrence were duration of preoperative atrial fibrillation (P = .01) and Cox maze procedure version (P = .001). There was no difference in actuarial 10-year survival between the Cox maze procedure versions. CONCLUSION: The Cox maze procedure remains the gold standard for the treatment of atrial fibrillation and has excellent long-term efficacy. The most significant predictor of late recurrence was duration of preoperative atrial fibrillation, suggesting that earlier surgical intervention would further increase efficacy.

Atrial tachyarrhythmias after the maze procedure: incidence and prognosis.

BACKGROUND: The Maze procedure restores normal sinus rhythm in the majority of patients. However, atrial tachyarrhythmias (ATA) are a common early complication after the operation. The purpose of this study was to define the incidence and natural history of ATA after the Maze procedure. METHODS: Complete medical records from 200 patients who underwent the Maze procedures (I, II, and III) from 1987 to 2002 were examined for all episodes of early postoperative ATA that occurred during the first 30 days after the procedure. Two electrophysiologists independently reviewed all postoperative 12-lead electrocardiograms. RESULTS: ATA occurred in 86 patients (43%) after the Maze procedure. Of the patients with ATA, 59% had atrial fibrillation (AF), 14% had atrial flutter (AFL), and 27% had both AF and AFL. Of the patients with AF or AFL, 20% and 5%, respectively, also had episodes of atrial tachycardia and supraventricular tachyarrhythmia. The peak incidence of early postoperative ATA was on postoperative day 8. The average duration of ATA was 5.7+/-5.0 days. Late recurrence of AF (>1 year postoperatively) occurred in 7.0% of patients who had early postoperative ATA and 8.8% of patients without early postoperative ATA (P=0.8). CONCLUSIONS: ATA occurred in 43% of patients after the Maze procedure. The tachyarrhythmias occurred primarily within 8 days after surgery and resolved within 3 weeks in almost all patients. There was no relationship between the incidence of early postoperative ATA and the late recurrence of AF.

The Cox maze III procedure for atrial fibrillation: long-term efficacy in patients undergoing lone versus concomitant procedures.

BACKGROUND: For the last decade, the Cox maze III procedure has been available for the treatment of atrial fibrillation. It is unknown whether the operation has similar efficacy in patients with lone atrial fibrillation compared with that in patients with atrial fibrillation associated with coronary, valve, or congenital heart disease. This study examined the long-term outcome of patients who underwent this procedure either as a lone operation or as a concomitant procedure. METHODS: From 1988 to 2001, 198 patients underwent a Cox maze III procedure; 112 were lone operations, and 86 were concomitant procedures. Major complications included renal failure, reoperation for bleeding, mediastinitis, stroke, and balloon pump insertion. Follow-up was performed by means of mail and telephone questionnaires with both the patients and their cardiologists. All patients who had any history of arrhythmia or who were taking medication had their rhythm documented by means of electrocardiography. RESULTS: The lone operation group was significantly younger (51.3 +/- 10.5 vs 58.8 +/- 9.9 years) and had a higher male/female ratio (4:1 vs 2:1). There was no difference in operative mortality between groups (1.8% vs 1.2%). At a follow-up of 5.4 +/- 2.9 years, 96.6% (172/178) of all patients were free of atrial fibrillation. There was no difference between the lone operation and concomitant procedure groups (95.9% vs 97.5%). CONCLUSION: The Cox maze III procedure has equivalent operative risk and long-term efficacy in patients undergoing both lone operations and concomitant procedures. The Cox maze III procedure remains the standard against which alternative procedures for atrial fibrillation must be judged.

The long-term outcome of patients with coronary disease and atrial fibrillation undergoing the Cox maze procedure.

BACKGROUND: A significant number of patients presenting for coronary revascularization have chronic atrial fibrillation. Although the Cox maze III procedure is the gold standard for the surgical treatment of this arrhythmia, few of these patients undergo atrial fibrillation operations at the time of their coronary bypass grafting. This study examined the long-term outcome of patients with ischemic heart disease who underwent the Cox maze procedure at our institution. METHODS: From 1990 to 2002, 47 patients undergoing operations for ischemic heart disease underwent a concomitant Cox maze III procedure. All patients underwent coronary bypass grafting, and 7 (15%) patients underwent coronary bypass grafting plus a mitral valve repair. Follow-up was performed by means of mail and telephone questionnaires with both the patients and their cardiologists. All patients who had any history of arrhythmia or who were taking medications had their rhythm documented by electrocardiogram. RESULTS: The mean age of these patients was 62 +/- 8 years, with a marked male predominance (45 men and 2 women). Twenty-eight (60%) of the patients had paroxysmal atrial fibrillation, and the remainder had persistent arrhythmias. The mean duration of atrial fibrillation was 7.6 +/- 6.5 years. The operative mortality in this series was 2%. Nine (19%) patients required postoperative pacemakers. At last follow-up (mean of 5.7 +/- 3.3 years), 98% of patients were free of atrial fibrillation. CONCLUSION: The Cox maze III procedure has a low operative mortality and excellent long-term efficacy in patients with ischemic heart disease. These data suggest a more widespread use of this procedure in these patients.