Lawrence L. Creswell

Hazards of postoperative atrial arrhythmias

Between January 1, 1986, and December 31, 1991, 4,507 adult patients underwent cardiac surgical procedures requiring cardiopulmonary bypass. Of these patients, 3,983 patients who did not undergo operation for supraventricular tachycardia and who were in normal sinus rhythm preoperatively form the study group for the present study. Postoperatively, all patients were monitored continuously for the development of arrhythmias until the time of hospital discharge. The incidence of atrial arrhythmias requiring treatment for the most commonly performed operative procedures were as follows: coronary artery bypass grafting, 31.9%; coronary artery bypass grafting and mitral valve replacement, 63.6%; coronary artery bypass grafting and aortic valve replacement, 48.8%; and heart transplantation, 11.1%. For all patients considered collectively, the risk factors associated with an increased incidence of postoperative atrial arrhythmias (p < 0.05 by multivariate logistic regression) included increasing patient age, preoperative use of digoxin, history of rheumatic heart disease, chronic obstructive pulmonary disease, and increasing aortic cross-clamp time. Postoperative atrial fibrillation was associated with an increased incidence of postoperative stroke (3.3% versus 1.4%; p < 0.0005), increased length of hospitalization in the intensive care unit (5.7 versus 3.4 days; p = 0.001) and postoperative nursing ward (10.9 versus 7.5 days; p = 0.0001), increased incidence of postoperative ventricular tachycardia or fibrillation (9.2% versus 4.0%; p < 0.0005), and an increased need for placement of a permanent pacemaker (3.7% versus 1.6%; p < 0.0005). These data provide a basis for targeting specific patient subgroups for prospective, randomized trials of therapeutic modalities designed to decrease the incidence of postoperative atrial arrhythmias.

Reexploration for bleeding is a risk factor for adverse outcomes after cardiac operations.

OBJECTIVE Although previous studies have included early reexploration for bleeding as a risk factor in analyzing adverse outcomes after cardiac operations, reexploration for bleeding has not been systematically examined as a multivariate risk factor for increased morbidity and mortality after cardiac surgery. Furthermore, multivariate predictors of the need for reexploration have not been identified. Accordingly, we performed a retrospective analysis of 6100 patients requiring cardiopulmonary bypass from January 1, 1986, to December 31, 1993. METHODS Eighty-five patients who had ventricular assist devices were excluded from further analysis because of the prevalence of bleeding and the significant morbidity and mortality associated with placement of a ventricular assist device, unrelated to reexploration. In the remaining 6015 patients, potential adverse outcomes analyzed included operative mortality, mediastinitis, stroke, renal failure, adult respiratory distress syndrome, prolonged mechanical ventilation, sepsis, atrial arrhythmias, and ventricular arrhythmias. To control for the confounding effects of other risk factors, we performed a multivariate logistic regression analysis. Potential covariates considered in the logistic model included age, sex, race, history of reoperation, urgency of the operation, congestive heart failure, prior myocardial infarction, renal failure, diabetes, hypertension, chronic obstructive pulmonary disease or stroke, and the bypass and crossclamp time. RESULTS The overall incidence of reexploration was 4.2% (253/6015). Four independent risk factors--increased patient age (p < 0.001), preoperative renal insufficiency (p = 0.02), operation other than coronary bypass (p < 0.001), and prolonged bypass time (p = 0.0.3)--were identified as predictors of the need for reexploration. The preoperative use of aspirin, heparin, or thrombolytic agents and the bleeding time were not identified as predictors. Reexploration for bleeding was identified as a strong independent risk factor for operative mortality (p = 0.005), renal failure (p < 0.0001), prolonged mechanical ventilation (p < 0.0001), adult respiratory distress syndrome (p = 0.03), sepsis (p < 0.0001), and atrial arrhythmias (p = 0.006). CONCLUSION These data indicate that meticulous attention to surgical hemostasis and possibly application of recently developed modalities designed to facilitate perioperative correction of coagulopathy could improve outcomes after cardiac operations.

Swallowing dysfunction after cardiac operations: Associated adverse outcomes and risk factors including intraoperative transesophageal echocardiography

The frequency, importance to patient outcomes, and independent predictors of postoperative swallowing dysfunction documented by barium cineradiography were examined in 869 patients undergoing cardiac operations over a 12-month period. Swallowing dysfunction was diagnosed in 34 patients (4% incidence) and was associated with documented pulmonary aspiration in 90% of these patients, increased frequency of pneumonia (p < 0.0001), need for tracheostomy (p = 0.0002), length of stay in the intensive care unit (p = 0.0001), and duration of hospitalization after the operation (p = 0.0001). Independent predictors of postoperative swallowing dysfunction determined by multivariate logistic regression included age (p < 0.001), length of tracheal intubation after the operation (p = 0.001), and intraoperative use of transesophageal echocardiography (p = 0.003). Dysfunctional swallowing after cardiac operations, a serious complication significantly related to postoperative respiratory morbidity and extended length of hospitalization, is more common in older patients. An association between intraoperative use of transesophageal echocardiography and swallowing dysfunction was also observed in our patients.

Intraaortic balloon counterpulsation: Patterns of usage and outcome in cardiac surgery patients

Between January 1, 1986, and May 6, 1991, 7,884 cardiac surgical procedures requiring cardiopulmonary bypass were performed at our institution, including 672 (9.8% of adult procedures) performed in 669 patients that were associated with preoperative (n = 240), intraoperative (n = 353), or postoperative (n = 79) use of an intraaortic balloon pump. The mean age of recipients was 65.3 years (range, 16 to 89 years). Intraaortic balloon pump usage increased during the study period from 6.4% of patients (83/1,298) in 1986 to 12.7% of patients (169/1,333) in 1990. The relative distribution between preoperative (mean, 35.7%), intraoperative (52.5%), and postoperative (11.8%) insertion remained nearly constant during the study period. The overall operative (30-day) mortality for patients with preoperative, intraoperative, or postoperative insertion of the intraaortic balloon pump was 19.6%, 32.3%, and 40.5%, respectively (X2 = 16.4; p less than 0.001). Although use of the intraaortic balloon pump in the intraoperative and postoperative settings is accompanied by a favorable outcome in most patients, the high associated mortality suggests the need for earlier use of the intraaortic balloon pump or other supportive measures such as the ventricular assist device.

Revascularization after acute myocardial infarction

BACKGROUND The optimal timing for coronary artery bypass grafting (CABG) after acute myocardial infarction (MI) remains controversial. METHODS We examined our experience retrospectively in 3,942 patients who underwent CABG between 1986 and 1993, including 2,296 patients after acute MI. RESULTS The operative mortality associated with increasing time intervals between MI and CABG were 9.1%, 8.3%, 5.2%, 6.5%, and 2.9%, for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. In comparison, the operative mortality was 2.5% for patients with no history of acute MI. The incidence of permanent stroke and perioperative MI were greater and the length of postoperative hospitalization was longer for patients undergoing CABG early after MI. For patients undergoing operation electively, however, the operative mortality associated with increasing time intervals between MI and CABG were less, at 0.0%, 3.6%, 2.1%, 6.4%, and 2.1% for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. For patients undergoing CABG within 14 days of MI, the operative mortality was 5.3% for those receiving an intraaortic balloon pump preoperatively for postinfarction angina, but 11.8% for those who underwent urgent/emergent operation without intraaortic balloon pump support. CONCLUSIONS Elective CABG can be accomplished with acceptable morbidity and mortality early after acute MI if an elective operation is possible. In addition, the intraaortic balloon pump should be used aggressively in patients with postinfarction angina to allow for elective rather than urgent/emergent operation.

An inverse approach to determining myocardial material properties

Passive myocardial material properties have been measured previously by subjecting test samples of myocardium to in vitro load-deformation analysis or, in the intact heart, by pressure-volume relationships. A new method for determining passive material properties, described in this paper, couples a p-version finite element model of the heart, a nonlinear optimization algorithm and a dense set of transmural measured strains that could be obtained in the intact heart by magnetic resonance imaging (MRI) radiofrequency tissue tagging. Unknown material parameters for a nonlinear, nonhomogeneous material law are determined by solving an inverse boundary value problem. An objective function relating the least-squares difference of model-predicted and measured strains is minimized with respect to the unknown material parameters using a novel optimization algorithm that utilizes forward finite element solutions to calculate derivatives of model-predicted strains with respect to the material parameters. Test cases incorporating several salient features of the inverse material identification problem for the heart are formulated to test the performance of the inverse algorithm in typical experimental conditions. Known true material parameters can be determined to within a small tolerance and random noise is shown not to affect the stability of the inverse solution appreciably. On the basis of these validation experiments, we conclude that the inverse material identification problem for the heart can be extended to solve for unknown material parameters that describe in vivo myocardial material behavior.

Coronary artery disease in patients with type A aortic dissection

The usefulness of preoperative coronary arteriography in patients with type A dissection of the aorta is controversial. To determine the prevalence of arteriosclerotic coronary artery disease in patients with type A dissection of the aorta, we reviewed our experience in 62 patients (42 with acute dissection and 20 with chronic dissection) who underwent operation between January 1, 1986, and December 31, 1993. Among 23 patients with acute dissection who underwent coronary arteriography, 8 (34.8%) had one or more coronary artery lesions causing a greater than 50% narrowing. Among 14 patients with chronic dissection who underwent coronary arteriography, 6 (42.9%) had one or more coronary artery lesions causing a greater than 50% narrowing. There were no fatal complications associated with coronary arteriography. Four patients with acute dissection and 6 patients with chronic dissection underwent coronary artery bypass grafting at the time of operative repair of the aortic dissection, with no operative deaths. On the basis of these findings and the success of combined coronary artery bypass grafting and aortic repair, we recommend that patients with an acute type A dissection who are in stable condition and all patients with a chronic type A dissection of the aorta should undergo preoperative coronary arteriography.

Mechanical dysfunction in the border zone of an ovine model of left ventricular aneurysm.

BACKGROUND The pathophysiology of regional mechanical dysfunction in the border zone (BZ) region of left ventricular aneurysm was studied in an ovine model using magnetic resonance imaging tissue-tagging and regional deformation analysis. METHODS Transmural infarcts were created in adult Dorsett sheep (n = 8) by ligation of the distal homonymous coronary artery and were allowed to mature into left ventricular aneurysms for 8 to 12 weeks. Animals were imaged subsequently using double oblique magnetic resonance imaging with radiofrequency tissue tagging. Short axis slices were selected for analysis that included predominantly the septal component of the aneurysm as well as adjacent BZ regions in the anterior and posterior ventricular walls. Dark grid patterns of magnetic presaturations were placed on the myocardium and tracked as they deformed during the diastolic, isovolumic systolic, and systolic ejection phases of the cardiac cycle. Regional ventricular wall strains were calculated in BZ regions and regions remote from the aneurysm and compared with strains measured in corresponding regions from normal control sheep (n = 6). RESULTS Diastolic midwall circumferential strains (fiber extensions) were relatively preserved, but abnormal circumferential lengthening strains were observed in the BZ regions during isovolumic systole. Peak circumferential strains ranged from 0.04 to 0.07 in the BZ regions but averaged -0.05 in the normal hearts (p = 0.002 for the anterior BZ and p = 0.001 for the posterior BZ). Midwall end-systolic fiber strains were depressed in the anterior BZ (-0.03 to -0.09 for the BZ versus -0.11 for the normal heart, p < 0.0001) but not in the posterior BZ (p = 0.19). CONCLUSIONS Our data support the theory that the stretching of BZ fibers during isovolumic systole contributed to a reduction in fiber shortening during systolic ejection and thus reduced the overall contribution of these fibers to forward ventricular output.

Myocardial material property determination in the in vivo heart using magnetic resonance imaging

Objectives: To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization.Background: Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dysfunction in disease states such as hypertrophy and heart failure. Accordingly, significant effort has been expended recently to characterize the material properties of myocardium in diastole. The present study defines a new technique for determining material properties of passive myocardium using finite element (FE) models of the heart, MRI tissue-tagging and nonlinear optimization. This material parameter estimation algorithm is employed to estimate nonlinear material parameters in thein vivo canine heart and provides the necessary framework to study the full complexities of myocardial material behavior in health and disease.Methods and results: Material parameters for a proposed exponential strain energy function were determined by minimizing the least squares difference between FE model-predicted and MRI-measured diastolic strains. Six mongrel dogs underwent MRI imaging with radiofrequency (RF) tissue-tagging. Two-dimensional diastolic strains were measured from the deformations of the MRI tag lines. Finite element models were constructed from early diastolic images and were loaded with the mean early to late left ventricular and right ventricular diastolic change in pressure measured at the time of imaging. A nonlinear optimization algorithm was employed to solve the least squares objective function for the material parameters. Average material parameters for the six dogs wereE=28,722 ± 15,984 dynes/cm2 andc=0.00182 ± 0.00232 cm2/dyne.Conclusion: This parameter estimation algorithm provides the necessary framework for estimating the nonlinear, anisotropic and non-homogeneous material properties of passive myocardium in health and disease in thein vivo beating heart.

Postoperative Atrial Arrhythmias: Risk Factors and Associated Adverse Outcomes

Atrial arrhythmias are the most common complication of cardiac surgical procedures today. Because of the additional hospital costs associated with these arrhythmias, owing to increased use of antiarrhythmic medications, diagnostic studies, and prolonged hospitalization, this subject continues to draw the interest of cardiac surgeons, cardiologists, insurance companies, and hospital administrators, among others. Despite many clinical studies, there is still no consensus regarding the best prevention strategy for these arrhythmias. We recently reviewed our experience with these arrhythmias, with the intent of identifying risk factors for the development of these arrhythmias and identifying any associated, potentially adverse, outcomes. We found that the incidence of postoperative atrial arrhythmias has increased to more than 35% in recent years. Risk factors for the development of postoperative atrial arrhythmias include increasing patient age, preoperative use of digoxin, history of rheumatic heart disease, chronic obstructive pulmonary disease, and increasing aortic cross-clamp (ischemic) time. Among patients with postoperative atrial arrhythmias, there was an increased rate of perioperative stroke, increased frequency of ventricular arrhythmias, increased need for the placement of a permanent pacemaker, and prolongation of the intensive care unit and total hospital length of stay.