Reversal of atrial mechanical stunning after cardioversion of atrial arrhythmias: implications for the mechanisms of tachycardia-mediated atrial cardiomyopathy

Proteolytic degradation of atrial sarcomere proteins underlies contractile defects in atrial fibrillation

Atrial fibrillation (AFib) is the most common cardiac rhythm disturbance, often treated via electrical cardioversion. Following rhythm restoration, a period of depressed mechanical function known as atrial stunning occurs, suggesting that defects in contractility occur in AFib and are revealed upon restoration of rhythm. This project aims to define the contractile remodeling that occurs in AFib. To assess contractile function, we used a canine atrial tachypacing model of induced AFib. Mass spectrometry analysis showed dysregulation of contractile proteins in samples from AFib compared with sinus rhythm atria. Atrial cardiomyocytes show reduced force of contraction, decreased resting tension, and increased calcium sensitivity in skinned single cardiomyocyte studies. These alterations correlated with degradation of myofilament proteins including myosin heavy chain altering force of contraction, titin altering resting tension, and troponin I altering calcium sensitivity. We measured degradation of other myofilament proteins, including cardiac myosin binding protein C and actinin, that show degradation products in the AFib samples that are absent in the sinus rhythm atria. Many of the degradation products appeared as discrete cleavage products that are generated by calpain proteolysis. We assessed calpain activity and found it to be significantly increased. These results provide an understanding of the contractile remodeling that occurs in AFib and provide insight into the molecular explanation for atrial stunning and the increased risk of atrial thrombus and stroke in AFib.NEW & NOTEWORTHY Atrial fibrillation is the most common cardiac rhythm disorder, and remodeling during atrial fibrillation is highly variable between patients. This study has defined the biophysical changes in contractility that occur in atrial fibrillation along with identifying potential molecular mechanisms that may drive this remodeling. This includes proteolysis of several myofilament proteins including titin, troponin I, myosin heavy chain, myosin binding protein C, and actinin, which is consistent with the observed contractile deficits.

Cardiac imaging correlates and predictors of stroke in patients with atrial fibrillation: a meta-analysis

BACKGROUND

New nonclinical parameters are needed to improve the current stroke risk stratification schemes for patients with atrial fibrillation. This study aimed to summarize data on potential cardiac imaging correlates and predictors of stroke or systemic embolism in patients with atrial fibrillation.

METHODS

MEDLINE, EMBASE, and Web of Science were searched to identify all published studies providing relevant data through 16 November 2022. Random effects meta-analysis method was used to pool estimates.

RESULTS

We included 64 studies reporting data from a pooled population of 56 639 patients. Left atrial spontaneous echo-contrast [adjusted odds ratio (aOR) 3.32, 95% confidence interval (CI) 1.98-5.49], nonchicken wing left atrial appendage (LAA) morphology (aOR 2.15, 95% CI 1.11-4.18), left atrial enlargement (aOR 2.12, 95% CI 1.45-3.08), and higher LAA orifice diameter (aOR 1.56, 95% CI 1.18-2.05) were highly associated with stroke. Other parameters associated with stroke included higher left atrial sphericity (aOR 1.14, 95% CI 1.01-1.29), higher left atrial volume (aOR 1.03, 95% CI 1.01-1.04), higher left atrial volume index (aOR 1.014, 95% CI 1.004-1.023), lower left atrial reservoir strain [adjusted hazard ratio (aHR) 0.86, 95% CI 0.76-0.98], higher left ventricular mass index (aOR 1.010, 95% CI 1.005-1.015) and E / e' ratio (aOR 1.12, 95% CI 1.07-1.16). There was no association between LAA volume (aOR 1.37, 95% CI 0.85-2.21) and stroke.

CONCLUSION

These cardiac imaging parameters identified as potential predictors of thromboembolism may improve the accuracy of stroke risk stratification schemes in patients with atrial fibrillation. Further studies should evaluate the performance of holistic risk scores including clinical factors, biomarkers, and cardiac imaging.

In Situ Transesophageal Echocardiography During Electrical Cardioversion in Patients With Atrial Fibrillation-Safety and Echocardiographic Findings

BACKGROUND

Transesophageal echocardiography (TEE) can reliably detect left atrial (LA) and LA appendage (LAA) thrombus in patients with atrial fibrillation (AF) before electrical cardioversion (ECV). However, evaluating cardiac and valve function pre-ECV can be challenging due to the increased and irregular heart rate. Additionally, post-ECV atrial stunning increases the risk of LAA thrombosis. Therefore, post-ECV TEE may allow for useful appendage, ventricular, and valve function assessment. However, the safety and usefulness of leaving the TEE probe in situ during ECV for post-ECV cardiac evaluation in clinical practice have not been previously evaluated.

METHODS

We analyzed 37 out of 86 consecutive patients who had the TEE probe left in situ, for clinical reasons, during ECV by a single operator between February 20, 2019, and January 3, 2023. We examined changes in left ventricular (LV) function, dynamic changes in valvular regurgitation, electromechanical coupling of the left atrium, and qualitative spontaneous echo contrast. We also assessed the presence of any complications related to the periprocedural TEE exam.

RESULTS

The mean age of the patients was 74 ± 9.65 years, and 29 (78%) were male. The periprocedural TEE time ranged from 7 to 55 minutes, with an average of 20.78 minutes. Immediately after ECV and restoration of normal sinus rhythm, there was an improvement in LV ejection fraction (47% ± 11.9% vs 40% ± 15.8%; P = .035). There was also a reduction in baseline mitral regurgitation of greater than moderate degree. However, spontaneous echo contrast worsened in the LAA in 11 (31.4%) patients. Additionally, 1 patient developed a new LAA thrombus, and 24 patients (72%) had evidence of electromechanical coupling with Doppler evidence of LA contraction. Clinically significant degenerative aortic and mitral stenosis were identified in 8% and mild or greater aortic regurgitation in 8% of patients post-ECV. No procedural complications were observed.

CONCLUSIONS

In situ TEE before, during, and after ECV is safe and provides useful clinical information regarding immediate cardiac changes after ECV, with diagnostic and therapeutic implications.

Efficacy of Low-Dose Isoproterenol Infusion for the Exclusion of a Left Atrial Appendage Thrombus in Patients With Dense Spontaneous Echo Contrast Caused by Atrial Fibrillation

BACKGROUND

In patients with atrial fibrillation (AF) and severe blood stasis in the left atrial appendage (LAA), dense spontaneous echo contrast (SEC) disturbs the distinct visualization of the LAA interior, thus making thrombus diagnosis inconclusive. We aimed to prospectively assess the efficacy and safety of a protocol for a low-dose isoproterenol (ISP) infusion to reduce SEC to exclude an LAA thrombus.Methods and Results: We enrolled 17 patients with AF and dense SEC (Grade 4 or sludge). ISP was infused with gradually increasing doses of 0.01, 0.02, and 0.03 μg/kg/min at 3-min intervals. After increasing the dose to 0.03 μg/kg/min for 3 min, or when the LAA interior was visible, the infusion was terminated. We reassessed the SEC grade, presence of an LAA thrombus, LAA function, and left ventricular ejection fraction (LVEF) within 1 min of ISP termination. Compared with baseline, ISP significantly increased LAA flow velocity, the LAA emptying fraction, LAA wall velocities, and LVEF (all P<0.01). ISP administration significantly reduced the SEC grade (median) from 4 to 1 (P<0.001). The SEC grade decreased to ≤2 in 15 (88%) patients, and the LAA thrombus was excluded. There were no adverse events.

CONCLUSIONS

Low-dose ISP infusion may be effective and safe to reduce SEC and exclude an LAA thrombus by improving LAA function and LVEF.

Proteolytic degradation of atrial sarcomere proteins underlies contractile defects in atrial fibrillation

Aims

Atrial fibrillation (AFib) is the most common cardiac rhythm disturbance. Treatment of AFib involves restoration of the atrial electrical rhythm. Following rhythm restoration, a period of depressed mechanical function known as atrial stunning occurs that involves decreased blood flow velocity and reduced atrial contractility. This suggests that defects in contractility occur in AFib and are revealed upon restoration of rhythm. The aim of this project is to define the contractile remodeling that occurs in AFib.

Methods and Results

To assess contractile function, we used a canine atrial tachypacing model of induced AFib. Mass spectrometry analysis showed dysregulation of contractile proteins in samples from AFib compared to sinus rhythm atria. Atrial cardiomyocytes showed reduced force of contraction in skinned single cardiomyocyte calcium-force studies. There were no significant differences in myosin heavy chain isoform expression. Resting tension is decreased in the AFib samples correlating with reduced full-length titin in the sarcomere. We measured degradation of other myofilament proteins including cMyBP-C, actinin, and cTnI, showing significant degradation in the AFib samples compared to sinus rhythm atria. Many of the protein degradation products appeared as discrete cleavage products that are generated by calpain proteolysis. We assessed calpain activity and found it to be significantly increased. Skinned cardiomyocytes from AFib atria showed decreased troponin I phosphorylation, consistent with the increased calcium sensitivity that was found within these cardiomyocytes.

Conclusions

With these results it can be concluded that AFib causes alterations in contraction that can be explained by both molecular changes occurring in myofilament proteins and overall myofilament protein degradation. These results provide an understanding of the contractile remodeling that occurs in AFib and provides insight into the molecular explanation for atrial stunning and the increased risk of atrial thrombus and stroke in AFib.

Isoproterenol-Assisted Differentiation Between Sludge and Organized Thrombus to Guide Left Atrial Appendage Occlusion

Percutaneous left atrial appendage occlusion (LAAO) is contraindicated in presence of left atrial appendage (LAA) thrombus. It is often difficult to separate LAA sludge from an organized thrombus on transesophageal echocardiography. The inability to differentiate sludge from thrombus leads to patients not receiving LAAO despite contraindication to long-term anticoagulation. Retrospective 6-month follow-up outcomes are reported on patients undergoing LAAO in presence of LAA sludge cleared by isoproterenol. This study showed no increased risk of transient ischemic attack/stroke in the 6 months following LAAO in the presence of LAA sludge, which was cleared with isoproterenol. This study suggests a role for isoproterenol in differentiating sludge from thrombus.

Post Procedural Peak Left Atrial Contraction Strain Predicts Recurrence of Arrhythmia after Catheter Ablation of Atrial Fibrillation

Background

Left atrial (LA) function can be impaired by the atrial fibrillation (AF) ablation and might be associated with the risk of recurrence. We sought to determine whether the post-procedural changes in LA function impact the risk of recurrence following AF ablation.

Methods

We retrospectively reviewed patients who underwent AF ablation between 2009 and 2011 and underwent transthoracic echocardiography before ablation, 1-day and 3-month after ablation. Peak left atrial contraction strain (PACS) and left atrial emptying fraction (LAEF) were evaluated during sinus rhythm and compared across the three time points. The primary endpoint was atrial tachyarrhythmia recurrence after ablation.

Results

A total of 144 patients were enrolled (mean age 61 ± 11 years, 77% male, 46% persistent AF). PACS and LAEF initially decreased 1-day following ablation but partially recovered within 3 months in PAF patients, with a similar trend in the PerAF patients. After median 24 months follow-up, 68 (47%) patients had recurrence. Patients with recurrence had higher PACS_1-day than that in non-recurrence subjects (-10.9 ± 5.0% vs. -13.4 ± 4.7%, p = 0.003). PACS_1-day -12% distinguished recurrence cases with a sensitivity of 67.7% and specificity of 60.5%. The Kaplan–Meier curves showed significant difference in 5-year cumulative probability of recurrence between those with PACS ≥ -12% and PACS < -12% (log rank p < 0.0001). Multivariate regression showed that PACS_1-day was an independent risk factor of arrhythmia recurrence.

Conclusions

Left atrial function deteriorates immediately following AF ablation and partially recovers in 3 months but remains abnormal in the majority of patients. PACS_1-day post procedure predicts arrhythmia recurrence at long-term follow-up.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12947-021-00250-5.

Usefulness of an isoproterenol infusion to differentiate a left atrial appendage thrombus in a patient with nonvalvular atrial fibrillation

A 78-year-old male with a history of a cardiac embolic stroke due to persistent AF and cerebral bleeding (CHADS2 score 4, HAS-BLED score 4) was referred to our hospital to implant a left atrial appendage (LAA) closure (LAAC) device. A trans esophageal echocardiography was performed and a high echoic lesion that was difficult to differentiate the spontaneous echo contrast or thrombus was found in the LAA cavity. After isoproterenol infusion, a high echoic lesion disappeared and we confirmed that it was not an LAA thrombus. Successful LAAC device implantation was performed without any thromboembolic events.

Hospital outcomes associated with new-onset atrial fibrillation during ICU admission: A multicentre competing risks analysis

PURPOSE

New onset atrial fibrillation (NOAF) in critically ill patients has been associated with increased short-term mortality. Analyses that do not take into account the time-varying nature of NOAF can underestimate its association with hospital outcomes. We investigated the prognostic association of NOAF with hospital outcomes using competing risks methods.

MATERIALS AND METHODS

We undertook a retrospective cohort study in three general adult intensive care units (ICUs) in the UK from June 2008 to December 2015. We excluded patients with known prior atrial fibrillation or an arrhythmia within four hours of ICU admission. To account for the effect of NOAF on the rate of death per unit time and the rate of discharge alive per unit time we calculated subdistribution hazard ratios (SDHRs).

RESULTS

Of 7541 patients that fulfilled our inclusion criteria, 831 (11.0%) developed NOAF during their ICU admission. NOAF was associated with an increased duration of hospital stay (CSHR 0.68 (95% CI 0.63-0.73)) and an increased rate of in-hospital death per unit time (CSHR 1.57 (95% CI 1.37-1.1.81)). This resulted in a strong prognostic association with dying in hospital (adjusted SDHR 2.04 (1.79-2.32)). NOAF lasting over 30 min was associated with increased hospital mortality.

CONCLUSIONS

Using robust methods we demonstrate a stronger prognostic association between NOAF and hospital outcomes than previously reported.

Atrial Strain and Strain Rate: A Novel Method for the Evaluation of Atrial Stunning

Background

Atrial fibrillation (AF) is the most common arrhythmia seen in adults. Atrial stunning is defined as the temporary mechanical dysfunction of the atrial appendage developing after AF has returned to sinus rhythm (SR).

Objectives

We aimed to evaluate atrial contractile functions by strain and strain rate in patients with AF, following pharmacological and electrical cardioversion and to compare it with conventional methods.

Methods

This study included 41 patients with persistent AF and 35 age-matched control cases with SR. All the AF patients included in the study had transthoracic and transesophageal echocardiography performed before and after. Septum (SEPsSR), left atrium (LAsSR) and right atrium peak systolic strain rate (RAsSR) were defined as the maximum negative value during atrial contraction and septum (SEPε), left atrium (LAε) and right atrium peak systolic strain (RAε) was defined as the percentage of change. Parameters of two groups were compared.

Results

In the AF group, 1st hour and 24th hour LAε, RAε, SEPε, LAsSR, RAsSR, SEPsSR found to be significantly lower than in the control group (LAε: 2.61%±0.13, 3.06%±0.19 vs 6.45%±0.27, p<0.0001; RAε: 4.03%±0.38, 4.50%±0.47 vs 10.12%±0.64, p<0.0001; SEPε: 3.0%±0.22, 3.19%±0.15 vs 6.23%±0.49, p<0.0001; LAsSR: 0.61±0.04s-¹, 0.75±0.04s-¹ vs 1.35±0.04s-¹, p<0.0001; RAsSR: 1.13±0.06s-¹, 1.23±0.07s-¹ vs 2.10±0.08s- ¹, p<0.0001; SEPsSR: 0.76±0.04s- ¹, 0.78±0.04s- ¹ vs 1.42±0.06 s- ¹, p<0.0001).

Conclusion

Atrial strain and strain rate parameters are superior to conventional echocardiographic parameters for the evaluation of atrial stunning in AF cases where SR has been achieved.

A Stunning Left Atrial Appendage Thrombus

BACKGROUND

Left atrial appendage thrombus formation is a known major complication of atrial fibrillation and atrial flutter which increases the risk of embolism and stroke. This risk of thrombosis is greatly increased with a lack of anticoagulation. After conversion to a normal sinus rhythm in these arrhythmias, the risk of thrombus formation in the left atrium persists through a phenomenon termed atrial myocardial stunning.

CASE

We present the case of a patient who previously underwent successful pulmonary vein isolation and was found to be in typical isthmus-dependent atrial flutter with a questionable recurrence of atrial fibrillation. The decision was made to return for atrial flutter ablation and for evaluation of prior pulmonary vein isolation. Initially, a transesophageal echocardiogram showed a normal ejection fraction, biatrial enlargement and no left atrial appendage thrombus. Ablation of the cavotricuspid isthmus was successfully accomplished with documented bidirectional block. A transesophageal echocardiogram probe was still in place prior to planned transseptal puncture for the evaluation of pulmonary veins. A large thrombus was now observed filling the left atrial appendage. Conclusion and Objective: Atrial stunning is a transient atrial contractile dysfunction that occurs whether sinus rhythm is restored spontaneously, electrically, pharmacologically or by ablation. We know after conversion that there is higher propensity to increased spontaneous echogenic contrast and decreased velocities; however, we do not have documented knowledge of exactly how soon after the conversion to a sinus rhythm a thrombus may be seen. We demonstrate a case of acute left atrial appendage thrombus formation immediately following the successful ablation of isthmus-dependent atrial flutter. Our report validates the belief that strategies of not interrupting anticoagulation prior to the conversion of these arrhythmias should be implemented.

Structural and Functional Remodeling of the Left Atrium: Clinical and Therapeutic Implications for Atrial Fibrillation

Atrial fibrillation (AF) is the most commonly encountered arrhythmia in clinical practice. Despite advances in our understanding of the pathophysiology of this complex arrhythmia, current therapeutic options remain suboptimal. This review aimed to delineate the atrial structural and functional remodeling leading to the perpetuation of AF. We explored the complex changes seen in the atria in various substrates for AF and the therapeutic options available to prevent these changes or for reverse remodeling. Here we also highlighted the emerging role of aggressive risk factor management aimed at the arrhythmogenic atrial substrate to prevent or retard AF progression.

High plasma human atrial natriuretic peptide and reduced transthoracic left atrial appendage wall-motion velocity are noninvasive surrogate markers for assessing thrombogenesis in patients with paroxysmal atrial fibrillation

BACKGROUND

The clinical relevance of examining human atrial natriuretic peptide (HANP) or left atrial appendage (LAA) wall-motion velocity during sinus rhythm in paroxysmal atrial fibrillation (AF) patients has not been clearly elucidated.

METHODS

The subjects were 38 patients with paroxysmal AF who underwent transesophageal and transthoracic echocardiography during sinus rhythm. The presence of spontaneous echocontrast (SEC) was examined with transesophageal echocardiography and LAA wall-motion velocity (LAAWV) was measured with transthoracic tissue Doppler echocardiography. Plasma HANP was measured within 3 hours after echocardiography.

RESULTS

Human atrial natriuretic peptide ranged from 12 to 106 pg/mL with an average of 43 ± 24 pg/mL and had a significant correlation with LAAWV (r = -0.57) or LAA flow velocity (r = -0.41). HANP was significantly higher in patients with SEC than in patients without SEC (64 ± 29 vs. 34 ± 15 pg/mL, P = 0.008) and LAAWV was significantly lower in patients with SEC than in patients without SEC (13 ± 5 vs. 20 ± 5 cm/sec, P = 0.002). HANP >44 pg/mL had a sensitivity of 73% and specificity of 89% for diagnosing SEC. SEC was more frequently observed (73%) in patients with HANP >44 pg/mL and/or LAAWV <10 cm/sec as compared with patients (11%) with normal HANP and LAA wall-motion velocity (P < 0.0001).

CONCLUSION

Higher plasma HANP and lower LAA wall-motion velocity may be noninvasive surrogate markers for assessing left atrial thrombogenesis during sinus rhythm in paroxysmal AF patients.

Effect of atrial fibrillation on atrial thrombogenesis in humans: impact of rate and rhythm

OBJECTIVES

We sought to assess the effect of atrial fibrillation (AF) on atrial thrombogenesis in humans by determining the impact of rate and rhythm.

BACKGROUND

Although AF is known to increase the risk of thromboembolic stroke from the left atrium (LA), the exact mechanisms remain poorly understood.

METHODS

We studied 55 patients with AF who underwent catheter ablation while in sinus rhythm; 20 patients were induced into AF, 20 patients were atrial paced at 150 beats/min, and 15 were control patients. Blood samples were taken from the LA, right atrium, and femoral vein at baseline and at 15 min in all 3 groups. Platelet activation (P-selectin) was measured by flow cytometry. Thrombin generation (thrombin-antithrombin [TAT] complex), endothelial dysfunction (asymmetric dimethylarginine [ADMA]), and platelet-derived inflammation (soluble CD40 ligand [sCD40L]) were measured using enzyme-linked immunosorbent assay.

RESULTS

Platelet activation increased significantly in both the AF (p < 0.001) and pacing (p < 0.05) groups, but decreased in control patients (p < 0.001). Thrombin generation increased specifically in the LA compared with the periphery in both the AF (p < 0.01) and pacing (p < 0.01) groups, but decreased in control patients (p < 0.001). With AF, ADMA (p < 0.01) and sCD40L (p < 0.001) levels increased significantly at all sites, but were unchanged with pacing (ADMA, p = 0.5; sCD40L, p = 0.8) or in control patients (ADMA, p = 0.6; sCD40L, p = 0.9).

CONCLUSIONS

Rapid atrial rates and AF in humans both result in increased platelet activation and thrombin generation. Prothrombotic activation occurs to a greater extent in the human LA compared with systemic circulation. AF additionally induces endothelial dysfunction and inflammation. These findings suggest that although rapid atrial rates increase the thrombogenic risk, AF may further potentiate this risk.

Electrogram organization predicts left atrial reverse remodeling after the restoration of sinus rhythm by catheter ablation in patients with persistent atrial fibrillation

BACKGROUND

Despite the informative nature of atrial fibrillation (AF) electrograms, electrophysiological aspects of predicting reversal of structural remodeling of the left atrium (LA) have not been evaluated.

OBJECTIVES

To identify predictors of reverse remodeling after restoration of sinus rhythm by catheter ablation in patients with persistent AF.

METHODS

This study included 90 patients with persistent AF and enlarged LA (left atrial volume indexed to body surface area [LAVi] ≥32 mL/m(2)). LAVi was measured by echocardiography before ablation and 12 months after sinus rhythm restoration. We divided 73 (81%) patients free from recurrences into 2 groups according to reduction in LAVi: responders, reduction ≥23% (n = 35); nonresponders, reduction <23% (n = 38). Serological testing and electrophysiological characteristics on electrocardiogram and magnetocardiogram were analyzed.

RESULTS

LAVi decreased from 43 ± 12 to 27 ± 7 mL/m(2) in responders and from 37 ± 8 to 33 ± 8 mL/m(2) in nonresponders. Higher LAVi at baseline (P = .01), lower age (59 ± 7 years vs 63 ± 7 years; P <.05), higher brain natriuretic peptide level (median = 92, interquartile range [IQR] = 98 pg/mL vs median = 60, IQR = 64 pg/mL; P = 0.01), higher atrial natriuretic peptide level (median = 73, IQR = 74 pg/mL vs median = 54, IQR = 70 pg/mL; P = .02), and higher organization index of AF signals (0.51 ± 0.11 vs 0.42 ± 0.09; P = .0001) were observed in responders. There was a linear correlation between organization index and % reduction in LAVi (R = 0.63; P <.0001). Multiple linear regression analysis showed relations between reverse remodeling and age (β = -0.28; P = .002), atrial natriuretic peptide level (β = 0.21; P = .03), and organization index (β = 0.53; P <.0001).

CONCLUSIONS

Electrogram organization was a robust predictor of reverse remodeling of the enlarged LA after sinus rhythm restoration by catheter ablation in patients with persistent AF.

AVE0118, Blocker of the Transient Outward Current ( I to ) and Ultrarapid Delayed Rectifier Current ( I Kur ), Fully Restores Atrial Contractility After Cardioversion of Atrial Fibrillation in the Goat

Background— The loss of atrial contractile function after cardioversion of atrial fibrillation (AF) contributes to the thromboembolic risk associated with AF. The newly developed blocker of the transient outward current ( I to ) and ultrarapid delayed rectifier current ( I Kur ) AVE0118 prolongs atrial action potential duration and might therefore enhance atrial contractility. We compared the ability of AVE0118 to restore atrial contraction after cardioversion of AF with the efficacy of conventional positive inotropic compounds in the goat model of AF.

Methods and Results— Eighteen goats were chronically instrumented with epicardial electrodes, a pressure transducer in the right atrium, and piezoelectric crystals to measure right atrial diameter. Atrial contractility and refractoriness and QT duration were measured before and after 1 week (3 to 8 days) of AF induced by repetitive burst pacing. The measurements were repeated after administration of digoxin (0.02 mg/kg), dobutamine (5 μg · kg −1 · min −1 ), the Ca 2+ sensitizer EMD57033 (1 mg · kg −1 · min −1 ), the L-type Ca 2+ channel agonist BayY5959 (0.1 mg · kg −1 · min −1 ), and AVE0118 (0.01 to 0.2 mg · kg −1 · min −1 ). The effect of AVE0118 on the configuration of atrial monophasic action potentials was determined for comparison. After 1 week of AF, atrial contractility during sinus rhythm or slow atrial pacing was reduced to <10%. Digoxin and dobutamine failed to increase atrial contractility. EMD57033 restored 41% and BayY5959 restored 48% of atrial contractility at baseline. BayY5959 significantly prolonged QT duration by 24.7%. AVE0118 enhanced atrial contraction to 156% of the baseline value. The positive inotropic effect was accompanied by a pronounced prolongation of atrial action potential duration and refractoriness, whereas QT duration remained unchanged.

Conclusions— Conventional positive inotropic drugs showed limited effect on atrial contractility after cardioversion of AF or produced QT prolongation. In contrast, the I to / I Kur blocker AVE0118 fully restored atrial contraction without proarrhythmic effects on the ventricle.

Antithrombotic therapy in atrial fibrillation: beyond the AFFIRM study

In the last few decades several clinical studies evaluated the efficacy and safety of different strategies for antithrombotic prophylaxis to prevent thromboembolic events in patients with atrial fibrillation (AF). Nowadays, a frequently debated point is related to the high embolic risk deriving from the asymptomatic and symptomatic AF recurrence after cardioversion or in paroxysmal AF, especially in patients with a large number of prolonged episodes of AF. In fact, after the recent AFFIRM and RACE trials, patients after successful cardioversion at risk for thromboembolism could also need lifelong anticoagulation. Considering this, should we anticoagulate all patients with clinical risk factors for thromboembolism with a single episode of AF, without considering the hemorrhagic risk? Based on recent trials, it is reasonable to hypothesize that long AF recurrences (> 48 h), both symptomatic and asymptomatic, are present mostly (if not exclusively) in patients with structural left atrial appendage (LAA) dysfunction and remodeling. Conversely, AF recurrences in patients without LAA dysfunction and remodeling, could be too short to allow thrombi formation in the LAA, and the anticoagulation could also be avoided. Once other clinical and echocardiographic determinants of stroke have been excluded, the LAA velocity could select patients with a normal appendage function at low embolic risk who could benefit from anti-aggregation and patients with irreversible appendage dysfunction, at high embolic risk, who need lifelong anticoagulation.

Anatomic and electrophysiological differences between chronic and paroxysmal forms of common atrial flutter and comparison with controls:

Whether chronic typical atrial flutter differs from paroxysmal atrial flutter regarding electrophysiological properties of reentry pathways and cardiac function remains unknown. If so, can remodeling due to long duration of persistently rapid atrial or ventricular rates explain these changes? The aim of the study was to compare RA local conduction velocities and heart function parameters between three groups: (1) chronic atrial flutter, (2) paroxysmal atrial flutter, and (3) controls. The study evaluated 52 patients undergoing radiofrequency ablation for typical atrial flutter. There were 35 patients with chronic atrial flutter (62.7 +/- 14 years) and 17 patients with paroxysmal atrial flutter (62.7 +/- 10 years). Underlying structural heart disease was present in 20 (57%) of 35 chronic atrial flutter patients and in 7 (41%) of 17 paroxysmal atrial flutter patients (P = 0.1). Chronic atrial flutter duration was 10.9 +/- 17 months and paroxysmal atrial flutter duration was 8.5 +/- 10 (P = 0.06). RA conduction velocity measurements were carried out before ablation during sinus rhythm under pacing (600-ms cycle length) with a 12-pole steerable catheter positioned in the high lateral RA (poles 11-12 [H6]), mid-lateral RA (poles 9-10 [H5]), and along the inferior vena caval tricuspid isthmus (poles 7-8 [H4]; 5-6 [H3]; 3-4 [H2]) with its distal electrode pair at the coronary sinus origin (pole 1-2 [H1]). Counter-clockwise RA conduction velocities were assessed from H6 to H1 and clockwise RA conduction velocities from H1 to H6. After successful ablation, RA and LA areas, LV volumes, LVEF, inferior vena caval tricuspid annulus, and coronary sinus tricuspid annulus (septal isthmus) lengths were measured by two-dimensional echocardiography. The control group included 12 patients without structural heart disease, referred for electrophysiological evaluation of AVN reentry. Counter-clockwise RA conduction velocities at the inferior vena caval tricuspid isthmus were lower in chronic atrial flutter than in paroxysmal atrial flutter (H4, 1.19 +/- 0.4 vs 1.89 +/- 1 m/s, P = 0.0051; H3, 1.14 +/- 0.4 vs 1.6 +/- 0.7 m/s, P = 0.0015; H2, 1.16 +/- 0.4 vs 1.53 +/- 0.5 m/s, P < 0.0056 and H1, 1.2 +/- 0.4 vs 1.5 +/- 0.4 m/s, P = 0.03, respectively). Counter-clockwise RA conduction velocities were identical at the high and mid-lateral RA. Counter-clockwise caval isthmus RA conduction velocities from H3 to H1 were significantly different between chronic atrial flutter and controls (H3, 1.14 +/- 0.4 vs 1.7 +/- 0.3 m/s, P = 0.0014; H2, 1.16 +/- 0.4 vs 1.83 +/- 0.4 m/s, P < 0.0001 and H1, 1.2 +/- 0.4 vs 1.94 +/- 0.4 m/s, P < 0.0001, respectively). A difference was found regarding clockwise isthmus RA conduction velocities between the two groups of atrial flutter and controls but not between chronic atrial flutter and paroxysmal atrial flutter. Respectively, chronic atrial flutter had greater RA and LA areas (24.5 +/- 5 vs 13 +/- 2 cm2; P < 0.0001 and 23 +/- 5 vs 16 +/- 3 cm2, P < 0.0001), LV end-systolic and end-diastolic volumes (50 +/- 25 vs 32 +/- 13 cm3, P = 0.0084 and 112 +/- 40 vs 85 +/- 25 cm3, P = 0.01), septal isthmus length (21 +/- 3 vs 13 +/- 2 mm, P < 0.0001), and inferior vena caval tricuspid isthmus length (39 +/- 6 vs 23 +/- 5 mm; P < 0.0001). Chronic common atrial flutter is characterized by more prolonged counter-clockwise conduction times and larger anatomic conduction pathways than the paroxysmal form, the causal relationship between electrophysiological and anatomic characteristics remains to be demonstrated.

Acute improvement of atrial mechanical stunning after electrical cardioversion of persistent atrial fibrillation: comparison between biatrial and single atrial pacing

OBJECTIVE

To evaluate the acute effects of atrial pacing at different pacing sites on mechanical stunning after cardioversion of atrial fibrillation (AF).

SETTING

Tertiary referral centre.

PATIENTS

20 patients with persistent AF were studied.

INTERVENTIONS

Spontaneous echo contrast (SEC), left atrial appendage emptying velocity (LAAEV), and left atrial appendage emptying fraction (LAAEF) were assessed by transoesophageal echocardiography (TOE) during AF, after conversion to sinus rhythm, and during atrial pacing from the right atrial appendage, left lateral atrium, and both atria simultaneously. Transmitral inflow velocity of the atrial wave (TMIF-A) by TOE and the maximum P wave duration in 12 lead ECG were also measured during sinus rhythm and atrial pacing.

MAIN OUTCOME MEASURES

Comparison of atrial mechanical function and P wave duration in 12 lead ECG during atrial pacing from different sites after cardioversion of AF.

RESULTS

Compared with sinus rhythm, atrial pacing at 80 beats/min increased LAAEV from mean (SD) 14.6 (10.1) to 33.4 (19.8) cm/s (p = 0.001), LAAEF from 13.8 (8.5) to 32.1 (11.2)% (p < 0.001), and TMIF-A from 24.6 (11.9) to 45.6 (21.0) cm/s (p < 0.001) and reduced SEC grade from 2.6 (1.0) to 1.6 (0.9) (p < 0.001). These effects had a positive force-frequency relation. Biatrial pacing produced the shortest P wave duration and resulted in the most significant improvement in atrial function (LAAEV, 33.2 (19.3) v 53.7 (23.9) cm/s, p = 0.0001; LAAEF, 31.9 (11.1) v 46.2 (12.6)%, p < 0.0001; TMIF-A, 37.7 (18.3) v 54.1 (21.2) cm/s, p < 0.001; SEC grade, 1.4 (1.1) v 0.8 (0.9), p = 0.001, right atrial appendage versus biatrial pacing).

CONCLUSIONS

Atrial pacing at increased rates can improve atrial mechanical function after cardioversion of persistent AF. Biatrial pacing may be the most effective technique to reverse atrial mechanical stunning.

Repetitive 4-Week Periods of Atrial Electrical Remodeling Promote Stability of Atrial Fibrillation

Background— Episodes of atrial fibrillation (AF) are known to cause both a rapid reduction in atrial refractoriness (atrial electrical remodeling) and a more delayed increase in AF stability thought to be due to a so-called “second factor.” The aim of this study was to quantify the effects and time course of such a factor on AF stability in the chronic goat model.

Methods and Results— AF was maintained in 6 goats by burst atrial pacing for 3 consecutive 4-week periods separated a mean of 6±2.1 days of sinus rhythm. Six days of sinus rhythm was just sufficient for refractoriness changes to reverse fully in all goats. Atrial effective refractory period, AF inducibility, and duration of individual episodes of AF were assessed at regular intervals. There was a progressive reduction from month 1 to 2 to 3 in the mean duration of burst pacing required to induce individual episodes of AF of 60 seconds (178±251, 110±102, and 21±30 hours), 1 hour (229±224, 136±104, and 68±51 hours), and 24 hours (277±218, 192±190, and 102±75 hours; P <0.03). The frequency with which AF was induced during extrastimulus pacing increased progressively from 16.7% in month 1 to 31.7% in month 2 and 46.9% in month 3 ( P <0.001).

Conclusions— Sequential 4-week periods of atrial fibrillation result in a progressive increase in AF stability independent of baseline atrial refractory period. This finding suggests the presence of a second factor in the self-perpetuation of AF with a time course comparable to that of AF-induced ultrastructural changes in the atria.

Atrial stunning: basics and clinical considerations

Conversion of atrial fibrillation and flutter to sinus rhythm results in a transient mechanical dysfunction of atrium and atrial appendage, termed atrial stunning. Atrial stunning has been reported with all modes of conversion of atrial fibrillation and flutter to sinus rhythm including both transthoracic and low energy internal electrical, pharmacological, and spontaneous cardioversion, and conversion by overdrive pacing and by radiofrequency ablation. Atrial stunning is a function of the underlying arrhythmia becoming apparent at the restoration of sinus rhythm, not the function of the mode of conversion, and does not develop after the unsuccessful attempts of cardioversion or the delivery of electric current to the heart during rhythms other than atrial fibrillation or flutter. Tachycardia-induced atrial cardiomyopathy, cytosolic calcium accumulation, and atrial hibernation are the suggested mechanisms of atrial stunning. Atrial stunning is at maximum immediately after cardioversion and improves progressively with a complete resolution within a few minutes to 4-6 weeks depending on the duration of the preceding atrial fibrillation, atrial size, and structural heart disease. Atrial stunning causes postcardioversion thromboembolism despite restoration of sinus rhythm. Duration of anticoagulation therapy after successful cardioversion should depend on the duration of atrial stunning. Lack of improvement in cardiac output and functional recovery of patients immediately after cardioversion is attributed to the atrial stunning. Verapamil, acetylstrophenathidine, isoproterenol, and dofetilide have been reported to protect from atrial stunning in animal and small human studies. Right atrium stunning is less marked and improves earlier than that of left atrium, resulting in a differential atrial stunning explaining the rare occurrence of pulmonary edema after cardioversion.

Reversal of Atrial Mechanical Dysfunction After Cardioversion of Atrial Fibrillation

Background— Atrial mechanical “stunning” develops after cardioversion of atrial fibrillation (AF) and is implicated in the genesis of thromboembolic complications. However, the mechanisms responsible for this phenomenon are poorly understood. Whether atrial mechanical dysfunction caused by AF can be reversed by pacing at increased rates or by pharmacological agents is unknown.

Methods and Results— Twenty-six patients with AF undergoing cardioversion were dichotomized prospectively on the basis of the duration of arrhythmia as short-duration (1 to 6 months) or long-duration (≥3 years) AF. Left atrial appendage emptying velocities (LAAEVs) and spontaneous echocardiographic contrast (LASEC) were assessed by transesophageal echocardiography during AF, after reversion to sinus rhythm, during atrial pacing at cycle lengths of 750 to 250 ms, after a postpacing pause, and with isoproterenol. In patients with short-duration AF, LAAEV decreased (42.0±2.7 to 18.5±2.0 cm/s; P <0.0001) and LASEC increased (0.9±0.3 to 2.2±0.3; P <0.01) with termination of AF; pacing increased LAAEV (48.3±4.1 cm/s; P <0.0001) and decreased LASEC (1.5±0.3; P <0.01); isoproterenol increased LAAEV (73.3±7.8 cm/s; P <0.0001) and decreased LASEC (0.3±0.2; P <0.01); and the postpacing pause increased LAAEV (68.3±3.8 cm/s; P <0.0001). In contrast, patients with long-duration AF demonstrated a significantly attenuated response of atrial mechanical function at each time point. With termination of AF, LAAEV decreased (19.1±2.6 to 8.2±1.0 cm/s; P =0.003) and LASEC increased (2.0±0.2 to 3.3±0.2; P <0.01); pacing increased LAAEV (18.4±2.7 cm/s; P <0.0001) and decreased LASEC (2.3±0.2; P <0.01); isoproterenol increased LAAEV (26.1±3.9 cm/s; P =NS to equivalent atrial rate) and decreased LASEC (1.0±0.3; P <0.01); and the postpacing pause increased LAAEV (27.2±2.4 cm/s; P =0.007).

Conclusions— Atrial pacing at increased rates and isoproterenol can reverse atrial mechanical stunning associated with short-duration AF. In contrast, long-duration AF is associated with an attenuated response to these maneuvers. These findings suggest a functional contractile apparatus in the mechanically remodeled atrium caused by AF; however, with longer durations of AF, additional factors may determine atrial mechanical function.

Time course for resolution of left atrial appendage stunning after catheter ablation of chronic atrial flutter

OBJECTIVES

This study assessed the time course of resolution of left atrial appendage (LAA) stunning after catheter ablation of chronic atrial flutter (AFL).

BACKGROUND

Although the presence of LAA stunning after ablation of chronic AFL calls for anticoagulation in the post-cardioversion period, limited information has been obtained, particularly regarding its duration.

METHODS

Sixteen patients who underwent ablation of chronic, pure AFL were studied, only five of whom had structural heart disease and one of whom had a reduced left ventricular ejection fraction. The LAA emptying velocities (LAAEV) and left atrial spontaneous echo contrast (SEC) were assessed using transesophageal echocardiography before, within 24 h after, one week after, and two weeks after ablation.

RESULTS

Within 24 h after ablation, the LAAEV decreased from 39 +/- 10 cm/s during AFL to 21 +/- 10 cm/s during sinus rhythm (p < 0.01), with eight patients (50%) having documented SEC. After one week, the LAAEV increased (39 +/- 17 cm/s, p < 0.01 vs. within 24 h) and SEC resolved in five of eight patients. After two weeks, the increase in LAAEV persisted (54 +/- 14 cm/s, p < 0.01 vs. 1 week) and SEC was no longer present in any of the patients. The numbers of patients with LAAEV >30 cm/s and absence of SEC were three within 24 h, 11 at one week, and 16 at two weeks after ablation.

CONCLUSIONS

Patients with chronic, pure AFL and preserved left ventricular function who will undergo catheter ablation may not require anticoagulation therapy for more than two weeks after the procedure because of the presence of forceful mechanical LAA contractions and the absence of SEC.