Title: Inadvertent Electrical Isolation of the Left Atrial Appendage During Catheter Ablation of Persistent Atrial Fibrillation
Topic: Arrhythmias
Date Posted: 3/2/2010
Author(s): Chan CP, Wong WS, Pumprueg S, et al.
Citation: Heart Rhythm 2010;7:173-180.
Clinical Trial: No
Study Question: What are the mechanisms of inadvertent isolation of the left atrial appendage (LAA) during atrial fibrillation (AF) ablation?
Methods: This study consisted of 11 patients (ejection fraction 0.43 ± 0.18, left atrial diameter 51 ± 8 mm) with persistent AF who had LAA conduction block during a procedure for AF (n = 8) or atrial tachycardia (AT) (n = 3). LAA isolation was defined as the complete elimination or dissociation of LAA potentials.
Results: LAA conduction block occurred during ablation at the Bachmann bundle region in six patients, mitral isthmus in three, LAA base in two, and coronary sinus in one. The mean distance from the ablation site to the LAA base was 5.0 ± 1.9 cm. LAA isolation was transient in all six patients in whom LAA conduction was monitored and was permanent in the four patients in whom conduction was not monitored during energy delivery. The remaining patient was noted to have LAA isolation during a redo procedure before any ablation. Nine of (82%) the 11 patients have remained arrhythmia-free without antiarrhythmic drugs at mean follow-up of 6 ± 7 months, and all have continued taking warfarin.
Conclusions: The authors concluded that electrical isolation of the LAA may occur during ablation of persistent AF and AT, and is due to disruption of the Bachmann bundle and its leftward extension.
Perspective: The primary finding of this study is that inadvertent LAA isolation may occur in patients undergoing a catheter ablation procedure for persistent AF or postablation AT, even if the ablation site is far removed from the appendage. The mechanism most likely is due to injury to the leftward extension of the Bachmann bundle and its branches that surround the base of the LAA. Although LAA conduction slowing was observed within seconds of initiation of RF current, the results of this study should not necessarily imply that the appendage may be isolated with a single lesion. It is more likely that LAA conduction was severely impaired either by prior ablation or as a result of a myopathic process in those patients, such that further injury (related to ablation) to the existing intra-atrial routes readily resulted in LAA isolation. Overall, the study suggests that monitoring LAA conduction during the procedure would be important in preventing LAA isolation. Debabrata Mukherjee, M.D., F.A.C.C.
Title: Analysis of the Impact of Early Surgery on In-Hospital Mortality of Native Valve Endocarditis: Use of Propensity Score and Instrumental Variable Methods to Adjust for Treatment-Selection Bias
Topic: Cardiovascular Surgery
Date Posted: 3/3/2010
Author(s): Lalani T, Cabell CH, Benjamin DK, et al.
Citation: Circulation 2010;121:1005-1013.
Clinical Trial: No
Study Question: Is there a beneficial role for early surgical intervention in patients with native valve infective endocarditis (IE)?
Methods: Using a prospective, multinational cohort of patients with definite native valve IE, the effect of early surgery on in-hospital mortality was assessed by propensity-based matching adjustment for survivor bias and by instrumental variable analysis. Patients were stratified by propensity quintile, paravalvular complications, valve perforation, systemic embolization, stroke, Staphylococcus aureus infection, and congestive heart failure.
Results: Of the 1,552 patients with native valve IE, 720 (46%) underwent early surgery and 832 (54%) were treated with medical therapy. Compared with medical therapy, early surgery was associated with a significant reduction in mortality in the overall cohort (12.1% [87/720] vs. 20.7% [172/832]) and after propensity-based matching and adjustment for survivor bias (absolute risk reduction [ARR] –5.9%, p < 0.001). With a combined instrument, the instrumental-variable adjusted ARR in mortality associated with early surgery was –11.2% (p < 0.001). In subgroup analysis, surgery was found to confer a survival benefit compared with medical therapy among patients with a higher propensity for surgery (ARR –10.9% for quintiles 4 and 5, p = 0.002) and those with paravalvular complications (ARR –17.3%, p < 0.001), systemic embolization (ARR –12.9%, p = 0.002), S. aureus native valve IE (ARR –20.1%, p < 0.001), and stroke (ARR –13%, p = 0.02), but not those with valve perforation or congestive heart failure.
Conclusions: This retrospective propensity-matched study suggests that early surgery for native valve IE is associated with an in-hospital mortality benefit compared with medical therapy alone.
Perspective: Traditional treatment of IE is extended antimicrobial therapy; surgical intervention is reserved for either specific early indications (persistent fevers or bacteremia despite appropriate antibiotic therapy, recurrent embolic events despite appropriate antibiotic therapy, or hemodynamic compromise as a result of valve destruction), or for later sequelae of valve destruction. This study, and some similar studies presented at recent meetings, suggests a possible shift in thinking, with a stated conclusion that earlier surgery is better. However, caveats abound. First, early surgery in this study was defined only as surgery during the initial hospitalization––not as surgery as soon as endocarditis is diagnosed. Second, as always (and unlike prospective, randomized trials), propensity score matching controls only for identified variables. At my institution, and I suspect at most others, there still needs to be a reason to operate ‘early.’ This means that, despite propensity score matching, patients operated early probably were different from those who were operated late (but in ways that were not identified). After the dust has settled, a fair conclusion might turn out to be that surgery to repair the damage done from IE might best be done after initial treatment of infection, but before months have passed. In the meantime, a bit of caveat emptor seems in order: Out of concern for early re-infection, it is doubtful that elective surgery for native valve IE should be done before a healthy amount of antimicrobial therapy has been administered. David S. Bach, M.D., F.A.C.C.