Background
Although transesophageal echocardiography is the definitive test for the detection of left atrial (LA) appendage thrombus, transthoracic echocardiography has yet to prove useful for the determination of increased risk for LA appendage thrombus formation. The authors hypothesized that higher LA volume and/or lower left ventricular ejection fraction (LVEF) might prove valuable as markers of increased risk for LA appendage thrombus formation and tested this hypothesis in a consecutive retrospective series of patients with atrial fibrillation undergoing both transthoracic and transesophageal echocardiography.
Methods
Three hundred thirty-four consecutive patients with atrial fibrillation undergoing transesophageal echocardiography for the detection of LA appendage thrombus were studied. Anticoagulation status, CHADS 2 scores, and echocardiographic parameters were catalogued. The relationship between the presence of LA appendage thrombus and covariates was analyzed using binary logistic regression.
Results
LA appendage thrombus was detected in 52 patients (15.6%). A higher CHADS 2 score (odds ratio, 1.45; P < .004), increased LA volume index (odds ratio, 1.02; P = .018), and lower LVEF (odds ratio, 1.02; P = .05) were significant predictors of LA appendage thrombus formation. LA appendage thrombus was not seen in patients with CHADS 2 scores ≤ 1, LVEFs > 55%, and a LA volume indexes < 28 mL/m 2 . A ratio of LVEF to LA volume index ≤ 1.5 produced 100% sensitivity for the presence of LA appendage thrombus.
Conclusions
The presence of LA appendage thrombus is related to both clinical and echocardiographic variables. Although no single echocardiographic variable discriminated between the presence and absence of LA thrombus, a normal LVEF and normal LA volume index were associated with the absence of LA appendage thrombus formation. For patients with atrial fibrillation with CHADS 2 scores ≤ 1, normal left ventricular systolic function and normal LA volume in combination may be a useful measure for the identification of patients at low risk for LA appendage thrombus formation.
Transesophageal echocardiography (TEE) has long been recognized as the definitive imaging technique for the identification of left atrial (LA) appendage (LAA) thrombus and commonly serves as a guide to cardioversion in patients with atrial fibrillation (AF) without prolonged anticoagulation. In patients with AF, the presence of LAA thrombus is known to be a powerful marker for increased stroke risk, even when other demographic and clinical risk factors are accounted for. Predicting the presence or absence of LAA thrombus, however, remains an elusive goal. Although LA dimension is higher and left ventricular (LV) ejection fraction (LVEF) is lower when LAA thrombus is present, neither factor is definitive. Other transthoracic echocardiographic parameters have thus far provided modest additional information and have not been thoroughly studied. In addition, the value of clinical risk factors for stroke in predicting LAA thrombus formation has been incompletely categorized.
LA volume index has been shown to be a powerful marker of clinical outcomes in patients with both AF and stroke. Increased LA volume index predicts greater incidence of AF overall, increased risk for AF recurrence after cardioversion, and elevated risk for first ischemic stroke. Even in patients with AF only, increased LA volume index predicts a higher frequency of adverse cardiac events. Accordingly, we hypothesized that LA volume index, perhaps in combination with other echocardiographic parameters, might prove valuable as a marker of increased risk for LAA thrombus formation, and we tested this hypothesis in a consecutive retrospective series of patients with AF undergoing both transthoracic echocardiography (TTE) and TEE. We also calculated a common measure of stroke risk, the CHADS 2 score, to examine whether clinical and echocardiographic factors combined would provide a more robust indicator than either variable alone.
Methods
Patients
The Hartford Hospital echocardiography database was used to identify patients with AF undergoing TEE for the detection of LAA thrombus before cardioversion from January 2003 through July 2010. Patients with paroxysmal AF as well as AF of varying duration were included in the analysis. Patients with AF undergoing TEE for the detection of LAA thrombus before cardioversion and concomitant TTE within 2 months of each other were eligible for inclusion in the study. The mean interval between studies was ±10 days; 88% of patients underwent both studies within 30 days of each other, and 29 patients (8.7%) underwent TTE after TEE. Four hundred thirty-nine patients meeting these entry criteria were identified. Patients with prosthetic heart valves ( n = 56), rheumatic mitral stenosis ( n = 11), complex congenital heart disease (tetralogy of Fallot, tricuspid atresia, d-transposition, Ebstein’s anomaly, previous complex congenital repair; n = 3), or hypertrophic obstructive cardiomyopathy ( n = 3) were excluded. Thirty-two patients with transthoracic echocardiograms inadequate for analysis were also excluded from the database, leaving a total of 334 patients available for analysis. For patients undergoing multiple transesophageal echocardiographic studies, only the first study was analyzed. The study was approved (including the waiving of informed consent) by the Hartford Hospital Institutional Review Board.
Clinical and demographic data, including age, international normalized ratio (INR) and/or partial thromboplastin time at the time of TEE, and CHADS 2 score, were catalogued. All INRs were obtained within 48 hours of TEE. CHADS 2 scores were at the time of TEE as previously described, with one point added for congestive heart failure, hypertension, age > 75 years, or diabetes mellitus and two points added for any history of stroke or transient ischemic attack. Transthoracic echocardiographic dimensions, calculated LV mass index, LVEF (by TTE), and body surface area were recorded. LV mass was calculated according the convention recommended by the American Society of Echocardiography: LV mass = 0.8 × {1.04[(LVIDd + ILWTd + SWTd) 3 − LVIDd 3 ]} + 0.6 g, where LVIDd is LV internal diastolic dimension, ILWTd is posterior wall thickness in diastole, and SWTd is septal wall thickness in diastole. When technically feasible, LVEF was measured from digitized Digital Imaging and Communications in Medicine images ( n = 228 [63%]) using an offline analysis system (Agfa Heartlab, Hackensack, NJ) by Simpson’s rule (method of discs) or estimated visually ( n = 134 [37%]) by a level 3–trained, National Board of Echocardiography–certified echocardiographer. For the calculation of LA volume, LA area and LA length in the apical four-chamber and two-chamber views were measured at end-systole. LA volume was calculated using the area-length method ( Figure 1 ) as
0.85 × LA are a 4 − chamber × LA are a 2 − chamber Shortest LA length .
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