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Strain and strain rate has been used in the echocardiographic research lab as a surrogate for understanding the physiologic functions of various chambers of the heart. After careful assessment of longitudinal, circumferential, and radial strain, through derivations of physical properties, a more specific surrogate for ejection fraction is developed. With our current knowledge, left atrial enlargement and increasing volumes have been shown to decrease strain and therefore physiologic function; these findings led to the independent association of enlarging left atrial size worse cardiovascular outcomes. Previous trials have shown reverse left atrial remodeling with antiarrhythmic therapy and restoration of sinus rhythm after cardioversion2 and catheter ablation. Marsan et al3 (2008) showed improvement of left atrial strain 3 months after catheter ablation, however, the current authors evaluated the effects of catheter ablation after long term follow up of 1 year.
The authors evaluated 148 patients who underwent catheter ablation for atrial fibrillation for drug refractory atrial fibrillation. The procedure protocol included electrical isolation of all pulmonary veins from the left atrium using an electroanatomic mapping system (CARTO). Endocardial mapping and ablation was performed with a 4 mm quadripolar mapping and ablation catheter, with an open loop irrigated tip. RF energy was applied outside of all the pulmonary vein ostia until a voltage of < 0.1 mV was achieved. A successful procedure included exhibition of entrance block during sinus rhythm or pacing from the coronary sinus.
Before the ablative procedure as well as after 12 months post-procedure, the patients underwent echocardiographic evaluation to assess left atrial strain. In 122 patients, who were a subgroup of patients that were in sinus rhythm before and after procedure, left atrial and left ventricular diastolic strains were evaluated. More specifically, left atrial volumes were measured on apical 2- and 4- chamber views. The maximum left atrial volume was determined as the largest volume prior to mitral valve opening and the smallest left atrial volume were therefore defined as the smallest volume after ejection from the left atrium. All collected volumes were indexed to BSA. In addition, left atrial ejection fraction was assessed by a defined formula. Patients that were felt to have exhibited significant atrial remodeling had to exhibit 15% or more reduction in the maximum left atrial volume after 12 months. Left atrial strain was also studied on 2- and 4- chamber views and left atrial longitudinal, circumferential, and radial strain was assessed via pre-defined echocardiographic techniques. These findings were averaged to acquire global left atrial strain and strain rate, which is the rate at which the left atrium deformation occurs.
At 12 month follow up, 67% (n=99) remained in sinus rhythm and 33% (n=49) had recurrence of atrial fibrillation. LA deformation properties showed a significant improvement with left atrial systolic strain increasing from 17 +/- 7% to 19 +/- 9% (p=0.001) and the strain rate increased from 1.1 +/- 0.4 1/s to 1.2 +/- 0.5 1/s (p=0.001). In addition, LA diastolic strain improved from -4 +/-3% to -6 +/- 6% with a strain rate improving from -1.4 +/-0.7 1/s to -1.6 +/-0.7 1/s (p=0.03) Furthermore, 63% (n=93) of patients were classified as responders, those who showed evidence of left atrial reverse remodeling, and 37% (n=55) were nonresponders. 69% (n=38) of the nonresponders experienced a recurrence of atrial fibrillation whereas only 12% (n=11) of the responders reverted to atrial fibrillation (p <0.001). Also, left ventricular systolic strain and strain rate improved significantly in responders (p < 0.05). After univariate and multivariate logistic regression analysis, left atrial strain and maximum left atrial volume were independent predictors of reverse remodeling after catheter ablation.
The results of the study suggest that patients who undergo catheter ablation of atrial fibrillation have the opportunity to exhibit left atrial remodeling which then entails improvement of left atrial strain and strain rate in addition to improved LV strain. Since strain can be considered a surrogate for ejection fraction, the authors concluded that catheter ablation can provide a beneficial outcome that can potentially improve cardiovascular outcomes by improving the systolic and diastolic properties of the heart.
1. Tops L, Delgado V, Bertini M, Marsan N, Den Uijl D, Trines S, Zeppenfeld K, Holman E, Shalij M; Bax J. Left atrial strain predicts reverse remodeling after catheter ablation for atrial fibrillation. J Am Coll Cardiol 2011;57:324-31.
2. Casaclang-Verzosa G, Gersh B, Tsang T. Structural and functional remodeling of the left atrium: clinical and therapeutic implications for atrial fibrillation. J Am Coll Cardiol 2008;51:1-11.
3. Tops L, Bax J, Zeppenfeld K, Jongbloed M, van der Wall E; Schalij M. Effect of radiofrequency catheter ablation for atrial fribrillation on left atrial cavity size. Am J Cardiol 2006;97:1220-2.
4. Abraham T, Dimaano V, Liang H. Role of tissue Doppler and strain echocardiography in current cynical practice. Circulation 2007;116:2597-609.
5. Eshoo S, Boyd A, Ross D, Marwick T, Thomas I. Strain rate evaluation of phasic atrial function in hypertension. Heart 2009;95:1184-91
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