Transthoracic Tissue Doppler Imaging of the Atria: A Novel Method to Determine the Atrial Fibrillation Cycle Length

Cardioversion of atrial fibrillation and atrial flutter revisited: current evidence and practical guidance for a common procedure

Cardioversion is widely used in patients with atrial fibrillation (AF) and atrial flutter when a rhythm control strategy is pursued. We sought to summarize the current evidence on this important area of clinical management of patients with AF including electrical and pharmacological cardioversion, peri-procedural anticoagulation and thromboembolic complications, success rate, and risk factors for recurrence to give practical guidance.

Relationship between atrial fibrillatory rate based on analysis of a modified base-apex surface electrocardiogram analysis and the results of transvenous electrical cardioversion in horses with spontaneous atrial fibrillation

OBJECTIVES

To compare the atrial fibrillatory rate (AFR) derived from a local right atrial intracardiac recording (RA-FR) and from a single-lead surface electrocardiogram (ECG) during atrial fibrillation (AF) and to evaluate the correlation with transvenous electrical cardioversion (TVEC) threshold (in Joules), number of shocks and cardioversion success rate in horses.

ANIMALS

ECGs and clinical records of horses with AF treated by TVEC. Horses were included if a simultaneous recording of the right atrial intracardiac electrogram and a modified base-apex ECG were available.

MATERIALS AND METHODS

Clinical records of horses with AF treated by TVEC were reviewed. Three-minute long episodes of simultaneous electrograms and surface ECG during AF were selected for analysis and compared using Bland-Altman analysis. The mean RA-FR was measured from the deflections on the intracardiac electrogram, while the AFR was extracted from the surface ECG using spatiotemporal QRS and T-wave cancellation.

RESULTS

Seventy-three horses satisfied the inclusion criteria. The mean difference between RA-FR and AFR was -13 fibrillations per minute (fpm), the 95% limits of agreement were between -66 and 40 fpm, and there was a moderate (ρ = 0.65) correlation between RA-FR and AFR (p < 0.001). Neither RA-FR nor AFR appeared to influence the TVEC cardioversion threshold or the number of TVEC shocks applied.

CONCLUSIONS

The AFR may allow non-invasive long-term monitoring of AF dynamics. Neither RA-FR nor AFR could be used to predict the minimal defibrillation threshold for TVEC.

Lack of Correlations between Electrophysiological and Anatomical-Mechanical Atrial Remodeling in Patients with Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) progressively leads to electrical remodeling (ER) and anatomical-mechanical remodeling (AR), whose relationships in humans remain poorly known.

METHODS

ER and AR were compared in patients undergoing percutaneous radiofrequency (RF) ablation for AF. ER was defined by right and left appendage activation rates as a surrogate for atrial refractory periods. AR was approached by left atrial (LA) diameters and area and left atrial appendage (LAA) area and contractile function (mean emptying flow velocity) (LAAFV) before RF ablation. Mean duration between successive LAA contractions was considered as LAA mechanical rate.

RESULTS

Forty-one patients (31 men, age: 64 ± 9 years) with paroxysmal (27%), persistent (61%), or long-persistent AF (12%) were prospectively included (ejection fraction: 44 ± 16%). Parameters exploring AR were highly correlated to each other: LA area (28 ± 7 cm(2) ), LAA area (5.7 ± 2.25 cm(2) ), LA transverse (49 ± 7 mm), and anteroposterior diameter (59 ± 13 mm) or LAAFV (29 ± 13 cm/s; P < 0.05 for each comparison). Parameters exploring ER were also highly correlated: right atrial appendage (RAA; 181 ± 39 ms) and LAA (176 ± 33 ms) activation rates (P < 0.0001). There was no significant correlation between any ER and AR parameter. Only LAA mechanical rate (174 ± 36 ms) was correlated to LAA or RAA activations rates (P ≤ 0.01).

CONCLUSION

ER and AR are not mutually related, atrial activation rate being not correlated to LA or LAA size or function. Thus, the mechanisms leading to AF-induced atrial remodeling may differ for anatomical and electrophysiological aspects.

Tissue velocity imaging-based atrial fibrillatory cycle length and wall motion for predicting atrial structural remodeling in patients undergoing catheter ablation

BACKGROUND

Atrial fibrillation (AF) causes atrial electrical and structural remodeling, which are linked to recurrence of AF after ablation. Atrial fibrillatory cycle length (AFCL) and AF wall motion velocity (AFW-V) obtained by tissue velocity imaging (TVI) might characterize such atrial electrical and structural remodeling. The purpose of this study was to assess the clinical and electrophysiologic correlates of these parameters and their relation to ablation outcomes.

METHODS AND RESULTS

The study group comprised 80 patients who underwent transthoracic echocardiography followed by AF ablation. Atrial TVI traces were used to determine AFCL-tvi and AFW-V-tvi at the left atrial septal wall. AFCL that was measured from intracardiac electrograms correlated well with AFCL-tvi (R=0.6094; P=0.0002). AFW-V-tvi was significantly lower and AFCL-tvi was significantly shorter in patients with non-paroxysmal AF than in those with paroxysmal AF (1.63±0.76 cm/s vs. 2.85±1.00 cm/s, respectively, P<0.0001; and 118.2±23.0 ms vs. 145.0±35.0 ms, respectively, P=0.0001). These findings held true for patients with and without post-ablation recurrence. Upon multivariate analysis, a reduced AFW-V-tvi remained the strongest predictor of post-ablation recurrence (hazard ratio for +1-cm/s change, 0.573; 95% confidence interval, 0.337-0.930; P=0.0234).

CONCLUSIONS

TVI of atrial fibrillatory wall motion might enhance the non-invasive characterization of atrial remodeling in patients with AF and thus be used for predicting AF recurrence after ablation.

The mechanical fibrillation pattern of the atrial myocardium is associated with acute and long-term success of electrical cardioversion in patients with persistent atrial fibrillation

BACKGROUND

Electrophysiological studies demonstrate that a short atrial fibrillation cycle length (AFCL) is related with poor outcome of electrical cardioversion (ECV) of atrial fibrillation (AF). We found previously that the mechanical AFCL (AFCL-tvi) and atrial fibrillatory velocity (AFV-tvi) may be determined noninvasively using color tissue velocity imaging (TVI) and closely relates to the electrophysiological AFCL.

OBJECTIVE

To evaluate the relation between AFCL-tvi, AFV-tvi, and success of ECV in patients with AF.

METHODS

We prospectively studied 133 patients with persistent AF by performing echocardiography before ECV and measured the AFCL-tvi and AFV-tvi in the right atrium and left atrium. Recurrent AF was monitored.

RESULTS

Nineteen (14%) patients had failure of ECV, 42 (32%) remained in sinus rhythm after 1-year follow-up, and 72 (54%) had a recurrence of persistent AF. Patients with immediate ECV failure had a lower median AFV-tvi measured in the right atrium than did patients with a successful ECV: 0.7 cm/s (0.2-1.0 cm/s) vs. 1.7 cm/s (0.9-2.8 cm/s) (P = .008). Patients with maintenance of sinus rhythm after 1 year had a longer AFCL-tvi measured in the left atrium than did patients with recurrence of AF (150 ms vs 137 ms; P = .017) and had a higher AFV-tvi in both atria (1.4 vs. 0.9 cm/s in the left atrium; P = .013 and 2.2 vs 1.4 cm/s in the right atrium; P = .011). Multivariate analyses showed that all atrial TVI parameters were independently associated with the maintenance of sinus rhythm after 1 year.

CONCLUSION

Higher atrial fibrillatory wall velocities and longer AFCLs determined by echocardiography are associated with acute and long-term success of ECV.

Noninvasive determination of atrial fibrillation cycle length by atrial colour tissue Doppler imaging in horses

REASONS FOR PERFORMING STUDY

Atrial fibrillation cycle length (AFCL) is an indicator of atrial electrical remodelling during atrial fibrillation (AF).

OBJECTIVES

To compare AFCL measured invasively from an intra-atrial electrogram (AFCLEGM ) with AFCL measured noninvasively by atrial colour tissue Doppler imaging (AFCLTDI ).

STUDY DESIGN

Prospective descriptive clinical study.

METHODS

Measurements were performed in 31 episodes of AF or flutter in 29 horses (588 ± 61 kg bwt, 9 ± 3 years old) admitted for transvenous electrical cardioversion. The AFCLEGM was measured from an intracardiac electrogram using a bipolar sensing/pacing electrode inserted into the right atrium. The AFCLTDI was measured from atrial colour tissue velocity curves in the following 5 regions: 1) left atrial free wall from a right parasternal 4-chamber view, 2) left atrial free wall from a short-axis view, 3) left atrial free wall from a left parasternal long-axis view, 4) interatrial septum, and 5) right atrial dorsal wall near the tuberculum intervenosum. The AFCLEGM and AFCLTDI from the 5 regions were compared using a one-way repeated-measures ANOVA with Bonferroni correction for multiple comparisons and calculation of the Bland-Altman mean bias and limits of agreement of AFCLEGM and AFCLTDI .

RESULTS

The AFCLEGM was 161 ± 18 ms in 29 AF episodes. Two horses showed atrial flutter and had an AFCLEGM of 244 and 324 ms. The mean bias between AFCLTDI and AFCLEGM ranged from -18 to +9 ms depending on the atrial wall region. The AFCLTDI was significantly shorter in the left atrial free wall from the right parasternal 4-chamber view and short-axis view than in the other regions (P<0.001).

CONCLUSIONS

Tissue Doppler imaging allows noninvasive measurement of AFCL in horses with AF and is able to identify spatial differences within the equine atria. Atrial fibrillation cycle length is an indicator of atrial electrical remodelling and is an important parameter to study AF pathophysiology or the effect of antiarrhythmic drugs.

Pathophysiological mechanisms of atrial fibrillation: a translational appraisal

Atrial fibrillation (AF) is an arrhythmia that can occur as the result of numerous different pathophysiological processes in the atria. Some aspects of the morphological and electrophysiological alterations promoting AF have been studied extensively in animal models. Atrial tachycardia or AF itself shortens atrial refractoriness and causes loss of atrial contractility. Aging, neurohumoral activation, and chronic atrial stretch due to structural heart disease activate a variety of signaling pathways leading to histological changes in the atria including myocyte hypertrophy, fibroblast proliferation, and complex alterations of the extracellular matrix including tissue fibrosis. These changes in electrical, contractile, and structural properties of the atria have been called "atrial remodeling." The resulting electrophysiological substrate is characterized by shortening of atrial refractoriness and reentrant wavelength or by local conduction heterogeneities caused by disruption of electrical interconnections between muscle bundles. Under these conditions, ectopic activity originating from the pulmonary veins or other sites is more likely to occur and to trigger longer episodes of AF. Many of these alterations also occur in patients with or at risk for AF, although the direct demonstration of these mechanisms is sometimes challenging. The diversity of etiological factors and electrophysiological mechanisms promoting AF in humans hampers the development of more effective therapy of AF. This review aims to give a translational overview on the biological basis of atrial remodeling and the proarrhythmic mechanisms involved in the fibrillation process. We pay attention to translation of pathophysiological insights gained from in vitro experiments and animal models to patients. Also, suggestions for future research objectives and therapeutical implications are discussed.