Quantitative Electrocardiography for Prediction Of
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QUANTITATIVE ELECTROCARDIOGRAPHY FOR PREDICTION OF POSTOPERATIVE ATRIAL FIBRILLATION AFTER CARDIAC SURGERY by FLORIAN RADER, M.D. Submitted in partial fulfillment of the requirements For the degree of Master of Science Clinical Research Scholars Program CASE WESTERN RESERVE UNIVERSITY January 2010 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Florian Rader, M.D. candidate for the Master of Science degree*. (signed) Regis E. McFadden (chair of the committee) Eugene H. Blackstone, M.D. Ottorino Costantini, M.D. Neal Dawson, M.D. (date) 10-28-2009 *We also certify that written approval has been obtained for any proprietary material contained therein. 2 Table of Contents List of Tables 4 List of Figures 5 Acknowledgments 6 List of Abbreviations 7 Abstract 9 Text Background and Significance 10 Specific aims 12 Methods 13 Results 21 Discussion 46 Limitations 54 Conclusions 54 References 55 3 List of Tables: Table 1: Patient characteristics 24 Table 2: Clinical predictors of postoperative atrial fibrillation 37 Table 3: ECG predictors of postoperative atrial fibrillation 38 4 List of Figures: Figure 1: Relationship of anatomic and ECG changes with POAF 11 Figure 2: Patient flow chart 22 Figure 3: Occurrence of POAF by days after surgery 33 Figure 4: Occurrence of POAF by surgery type 34 Figure 5: ROC curve of final prediction model 35 Figure 6: Calibration curve of final prediction model 36 Figure 7: Adjusted Co-plots of ECG predictors 39 Figure 8: Unadjusted and adjusted co-plot of P wave amplitude 41 Figure 9: Nomogram of final prediction model 42 Figure 10: Nomogram of prediction model with pre-op variables 43 Figure 11: Calibration curve of model without ECG predictors 45 Figure 12: Left atrial sizes by P wave amplitude in aVR 48 Figure 13: Correlation matrix (P wave amplitude, aVR, and left atrial volume) 49 5 Acknowledgments: I thank Dr. Rajeswaran, staff statistician of the Department of Quantitative Health Sciences at Cleveland Clinic for the continued support of my project. In addition, I want to thank my mentors, specifically Dr. Eugene Blackstone, Dr. Otto Costantini and Dr. Neal Dawson for making themselves available and discussing this project in multiple hour-long sessions despite their busy schedules. 6 List of abbreviations: ABDT = Angiotensin blocking drug therapy ACE = Angiotensin converting enzyme AF = Atrial fibrillation ARB = Angiotensin II receptor blocker AVR = Aortic valve replacement BPM = beats per minute BMI = Body mass index BUN = Blood urea nitrogen CA = Coronary artery CABG = Coronary artery bypass graft surgery CC = cubic centimeters CM = Centimeter COPD = Chronic obstructive pulmonary disease CR = Creatinine CVIR = Cardiovascular Information Registry CVA = Cerebral vascular accident DL = Deciliter ECG = Electrocardiogram FFP = Fresh frozen plasma g = gram ICD = Implanted cardioverter-defibrillator 7 KG = Kilogram LA = Left atrium LAD = Left anterior descending coronary artery LCX = Left circumflex coronary artery LVH = Left ventricular hypertrophy m = meter mg = milligram ml = milliliter mmHg = millimeter mercury µV = microvolt MUSE = Marquette Universal System of Electrocardiography MV = Mitral valve MVR= Mitral valve replacement OR = Odds ratio POAF = Postoperative atrial fibrillation RBC = Red blood cell RCA = Right coronary artery ROC = Receiver operating characteristics 8 Quantitative Electrocardiography for Prediction of Postoperative Atrial Fibrillation after Cardiac Surgery Abstract by FLORIAN RADER, M.D. Background: Postoperative atrial fibrillation (POAF) after cardiac surgery is a common marker of poor outcomes and can be reduced with medical prophylaxis. Methods: Quantitative ECG measurements and clinical patient characteristics predictive of POAF were identified with stepwise logistic regression and 500-fold bagging in a cohort of patients undergoing coronary artery bypass and/or valve surgery. Results: 4762 (35%) of 13416 patients developed POAF. Independent ECG predictors were a less negative P wave amplitude in lead aVR (OR 1.46, CI 1.32- 1.61) and a larger P wave amplitude in lead V1 (OR 1.25, CI 1.16-1.36, per 0.1 mV). Greater age and left atrial volume, prior episodes of atrial arrhythmias, and valvular surgery were risk factors; black race and hypothyroidism were protective from POAF. Conclusion: P wave amplitude in lead aVR and V1 are important predictors of postoperative atrial fibrillation after cardiac surgery and in combination with clinical predictors can guide prophylactic medication use. 9 Background and Significance: Atrial fibrillation (AF) is the most common arrhythmia after cardiac surgery occurring in 16% to 53%(1,2) of patients with the highest incidence on day 2 after surgery(3). Postoperative AF (POAF) is associated with higher morbidity (i.e. acute myocardial infarction, stroke, worsening congestive heart failure, re- intubation), mortality, length of hospital stay and costs(4-7). In a study by Aranki et al. POAF after coronary bypass graft surgery (CABG) was associated with prolongation of hospital stay by 4.9 days and addition of $10,055 in hospital costs(4). Prophylactic medications such as amiodarone, beta blockers and sotalol(8-11) are available, but they bear the potential of significant adverse effects (i.e. bradycardia, hypotension) and should therefore only be used in patients at high risk. The method of quantitative electrocardiography has been applied to predict mortality in left ventricular hypertrophy(12) and acute coronary syndrome(13,14). Although the use of P wave analysis to predict POAF has been proposed, it remains controversial. Passman and colleagues used ECG measurements similar to ours and found P wave duration in V1 and PR interval to be predictive. The study was limited by small sample size of 152 patients and adjustment for only few variables(15). Amar and colleagues reported P wave duration and PR interval the least discriminatory out of all independent predictors of POAF(16). However, both studies showed a promising signal of quantitative ECG measurements being a useful component of preoperative risk assessment of postoperative supraventricular arrhythmias. Multiple studies demonstrated the 10 association of POAF with echocardiographic measures such as left atrial enlargement(1,17), presence of left ventricular hypertrophy(18,19) and decreased left ventricular ejection fraction(20) (Figure 1). ECG variables such as the P-wave, QRS-duration, and ECG criteria for left ventricular hypertrophy are almost always available (even in acute situations) prior to cardiac surgery, correlate well with the echocardiographic measurements(21) and are associated with little cost. Furthermore we postulate that ECG measurements may have diagnostic properties that go beyond the role of a surrogate of anatomical features, but may also mirror the electrolyte and autonomic nerve milieu, myocardial tissue inflammation, ischemia and fibrosis. A recent study from the Framingham cohort identified PR interval as an independent predictor for development of non-operative atrial fibrillation(22). Elevated left ventricular Valve disease Ischemia afterload Mechanisms Left ventricular Left ventricular Elevated left Left atrial remodeling & Pathophysiologic remodeling hypertrophy atrial pressure enlargement Prolongation of ECG indices of PR interval, P- wave QRS duration left ventricular morphology hypertrophy ECG Measures POSTOPERATIVE ATRIAL FIBRILLATION Figure 2: Proposed pathways of myocardial remodeling and associated ECG findings leading to postoperative atrial fibrillation 11 Specific Aims: 1. Specific aim #1: To describe the association of quantitative measurements of P wave, PR interval and QRS complex, as surrogates for pathological structural and electrical remodeling of the heart, with POAF. 2. Specific aim #2: To describe the association of clinical patient characteristics, such as medical comorbidities, procedure related variables and echocardiographic data, with POAF. 3. Specific aim #3: To create a prediction rule, which can identify patients who are at high risk of developing POAF after cardiac surgery. Methods: 1. Study Sample: 1.1. Inclusion criteria: • Patients undergoing isolated CABG or isolated heart valve surgery or a combination of these at Cleveland Clinic from 1997 to 2003 (n=14,258). • Patients in sinus rhythm prior to surgery as determined by clinical history and the last ECG prior to surgery. 1.2. Exclusion criteria: • Patients in AF or atrial flutter at time of surgery (defined as having permanent AF or AF/atrial flutter on their last ECG prior to surgery, n= 173). • Patients with an implanted pacemaker or cardioverter-defibrillator (n=89). • Patients with missing ECG variables due to corrupted ECG data (n=580). 12 Rationale for exclusion of patients: Patients in chronic AF could not be considered at risk for new onset POAF. To exclude all patients who are in AF prior to their surgery, AF on the last ECG (recorded no more than 30 days before surgery) indicated non-eligibility. Patients with an implanted pacemaker by history were excluded at time of database query and additional 89 patients had evidence of a pacemaker on their last ECG prior to surgery and were excluded due to the lack of interpretability of their ECG tracings (pacemakers can alter all elements of the ECG measurements of interest in an unpredictable fashion depending on the amount of pacing in the atrium and ventricle). Patients with missing ECG data caused by corrupted data files (surgery dates prior to 1/7/1991