Average e' velocity on transthoracic echocardiogram is a novel predictor of left atrial appendage sludge or thrombus in patients with atrial fibrillation

PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF)-the most common sustained cardiac arrhythmia-increases thromboembolic stroke risk 5-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C (protein phosphatase 1 regulatory subunit 12C)-the PP1 (protein phosphatase 1) regulatory subunit targeting MLC2a (atrial myosin light chain 2)-causes hypophosphorylation of MLC2a and results in atrial hypocontractility.

METHODS

Right atrial appendage tissues were isolated from human patients with AF versus sinus rhythm controls. Western blots, coimmunoprecipitation, and phosphorylation studies were performed to examine how the PP1c (PP1 catalytic subunit)-PPP1R12C interaction causes MLC2a dephosphorylation. In vitro studies of pharmacological MRCK (myotonic dystrophy kinase-related Cdc42-binding kinase) inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with electrophysiology studies.

RESULTS

In human patients with AF, PPP1R12C expression was increased 2-fold versus sinus rhythm controls (P=2.0×10-2; n=12 and 12 in each group) with >40% reduction in MLC2a phosphorylation (P=1.4×10-6; n=12 and 12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF (P=2.9×10-2 and 6.7×10-3, respectively; n=8 and 8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a and dephosphorylation of MLC2a. Mice treated with lentiviral PPP1R12C vector demonstrated a 150% increase in left atrial size versus controls (P=5.0×10-6; n=12, 8, and 12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in mice treated with lentiviral PPP1R12C vector was significantly higher than in controls (P=1.8×10-2 and 4.1×10-2, respectively; n=6, 6, and 5).

CONCLUSIONS

Patients with AF exhibit increased levels of PPP1R12C protein compared with controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

Myosin Light Chain Dephosphorylation by PPP1R12C Promotes Atrial Hypocontractility in Atrial Fibrillation

Background

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility.

Methods

Right atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation. In vitro studies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies.

Results

In human patients with AF, PPP1R12C expression was increased two-fold versus SR controls ( P =2.0×10 -2 , n=12,12 in each group) with > 40% reduction in MLC2a phosphorylation ( P =1.4×10 -6 , n=12,12 in each group). PPP1R12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF ( P =2.9×10 -2 and 6.7×10 -3 respectively, n=8,8 in each group). In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls ( P =5.0×10 -6 , n=12,8,12), with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls ( P =1.8×10 -2 and 4.1×10 -2 respectively, n= 6,6,5).

Conclusions

AF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key determinant of atrial contractility in AF.

Relationship between left ventricular diastolic function and the risk of left atrial appendage thrombus in patients with nonvalvular atrial fibrillation

In patients with nonvalvular atrial fibrillation (NVAF), the impact of left ventricular diastolic function on the risk of left atrial appendage (LAA) thrombus has rarely been studied. This prospective study aimed to investigate the relationship between diastolic function and the risk of LAA thrombus in patients with NVAF. Seventy-six patients with NVAF admitted to receive radiofrequency catheter ablation were prospectively enrolled. All the patients underwent transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) in 24 h before ablation. Diastolic function was estimated by TTE including left atrial volume index (LAVI) and E/e', as well as invasive left atrial pressure (LAP) measured during the ablation procedure. LAA peak emptying velocity (LAA-PEV) and the intensity of spontaneous echo contrast (SEC) were determined by TEE. Average E/e', LAVI and mean LAP had a significant positive correlation with the intensity of SEC, the coefficient of correlation were 0.344 (p = 0.002), 0.416 (p < 0.001) and 0.402 (p < 0.001), respectively. After adjustment for CHA₂DS₂-VASc score and type of AF, multivariate regression analysis revealed that increased LAP (OR 1.144, 95% CI 1.012-1.293, p = 0.031) independently correlated with the risk of LAA thrombus (SEC ≥ Grade 2). LAA-PEV showed a significantly inverse relationship with mean LAP in patients with AF (r =  - 0.525, p < 0.001), and in the assessment of elevated LAP with TEE, the LAA-PEV cut-off of 0.40 m/s had a sensitivity of 80%, specificity of 81%. Left ventricular diastolic dysfunction may constitute a potential risk for LAA thrombus and stroke. Furthermore, evaluation of LAA emptying with use of TEE is helpful for assessing the LAP status of patients with AF.

Evaluating the novel parameters for assessing the LAA function and thrombus formation with nonvalvular atrial fibrillation

The dysfunction of left atrial appendage (LAA) is prone to form thrombus when atrial fibrillation (AF) sustained more than 48 h. Traditional 2D-TEE (transesophageal echocardiography) can not accurate evaluate the function of LAA. The purpose of this study is to analyze the relationship of LAA function parameters and thrombus formation in patients with non-valvular atrial fibrillation (NVAF) by real-time three-dimensional transesophageal echocardiography (RT-3D-TEE). High risk patients can be identified according to the characteristics of ultrasonic index in patients with left atrial appendage thrombosis, which has important clinical value and significance in the risk assessment, guiding treatment and judging prognosis. We examined the relationship between the echocardiographic parameters of LAA function and the incidence of thrombus in 102 NVAF patients. They underwent RT-3D-TEE and left atrial appendage thrombus (LAAT)/severe spontaneous echocardiographic contrast (SSEC) was found in 67 patients (thrombus group) but absent in the remaining 35 patients (non-thrombus group). After measured by QLAB software, the LAA functional parameters were significantly associated with LAAT/SEC formation. Univariate analysis indicated that AF time, LAD, LVEF, LAA-OAmax, LAAVmax, LAAVI and LAAEF demonstrated a positive association (P < 0.05). However, logistic regression analysis identified that AF time (OR:1.73, P < 0.05)、LAAEF (OR:4.09, P < 0.01)and LAAVI (OR:3.28, P < 0.01) were independent predictors of LAAT/SSEC. In patients with nonvalvular atrial fibrillation, echocardiographic parameters of LAA function are significantly associated with LAAT/SSEC.

Diastolic function in young patients with cryptogenic stroke: A case-control pilot study

BACKGROUND

Ischaemic stroke in young individuals often remains cryptogenic. In this pilot study, we investigated, whether advanced echocardiography methods could find differences in the diastolic function between young cryptogenic stroke patients and stroke-free controls.

METHODS

We recruited 30 cryptogenic ischaemic stroke patients aged 18-49 and 30 age- and sex-matched stroke-free controls among participants of the Searching for Explanations for Cryptogenic Stroke in the Young: Revealing the Etiology, Triggers, and Outcome (SECRETO) study (NCT01934725). We measured diastolic function parameters derived from speckle tracking strain rate, Doppler techniques and 4D volumetry. We also performed statistical analyses comparing only the highest and lowest tertile of cases and controls for each parameter.

RESULTS

None of our patients or controls had diastolic dysfunction according to ASE/EACVI criteria. However, compared to stroke-free controls, the stroke patient group had lower E/A ratio of mitral inflow, lower lateral and mean e', lower A/a' ratio, lower strain rate in early diastole and lower speckle tracking-derived e/a ratio. When comparing the lowest tertiles, patients also had a lower peak filling rate by 4D volumetry, a lower peak early filling fraction (fraction of left ventricular filling during early diastole), and lower velocities in a series of the tissue Doppler-derived diastolic parameters and blood flow/tissue velocity ratios.

CONCLUSION

Our study displayed subtle differences in diastolic function between patients and stroke-free controls, which may play a role in early-onset cryptogenic stroke. The differences were clearer when the lowest tertiles were compared, suggesting that there is a subgroup of young cryptogenic stroke patients with subclinical heart disease.

Disappearance of an anticoagulation-resistant left atrial appendage thrombus after administration of low-dose pimobendan

Anticoagulation therapy is essential for preventing thrombus formation in the left atrial appendage (LAA) and subsequent ischemic strokes in patients with atrial fibrillation (AF). The complete disappearance of any existing LAA thrombi is crucial before AF ablation. Currently, warfarin and direct oral anticoagulants are widely used for this purpose. However, treatment strategies for anticoagulation-resistant LAA thrombi are not well established. Here, we present a case of an 85-year-old male who was scheduled to undergo AF ablation. He developed an LAA thrombus that was resistant to 300 mg/day of dabigatran. Low-dose pimobendan was prescribed in addition to dabigatran; three months later, the thrombus was dissolved successfully. This case demonstrates the potential efficacy of a low-dose oral inotrope for treating an anticoagulation-resistant LAA thrombus. <Learning objective: Treatment strategies for anticoagulation-resistant left atrial appendage thrombi are not well established. This case demonstrates that a low-dose oral inotrope, such as pimobendan, is capable of dissolving such thrombi and is a potentially useful treatment modality.>.

Predictors of movable type left atrial appendage thrombi in patients with atrial fibrillation

Left atrial appendage thrombi (LAAT) are the main cause of thromboembolic events. Especially, movable type LAAT is high-risk for thromboembolic events. We aimed to investigate the predictors of the movable type LAAT in patients with atrial fibrillation (AF). We retrospectively studied 827 consecutive patients who underwent transthoracic echocardiography (TEE) prior to cardioversion or catheter ablation for AF. Sixty-nine patients who underwent cardiac surgery or significant valvular disease were excluded. The remaining 758 patients (age 67.6 ± 9.3, 535 males) were included in this study. Clinical data were evaluated at the time of TEE. The LAAT were classified into movable and fixed type LAAT by three independent observers who did not know clinical data. LAAT were detected in 57 (11 with movable and 46 with fixed type) of 758 patients (7.5%). Patients with movable type LAAT had an elevated E/e' ratio, lower left ventricular ejection fraction (LVEF), larger left atrial volume index, elevated C-reactive protein, higher prevalence of non-paroxysmal AF, patients taking warfarin (73% vs. 21%, P < 0.0001), and structural heart disease than control group (fixed type LAAT and without LAAT). On multivariate analysis, E/e' ratio, LVEF, and taking warfarin were significantly associated with movable type LAAT. The rate of movable type LAAT was the highest (7 of 49 patients, 14.3%) in patients with elevated E/e' ratio (> 12.7) and decrease LVEF (< 44%). E/e' ratio and LVEF could predict movable type LAAT in patients with AF. High-risk patients might need powerful antithrombotic therapy or taking early TEE.

Atrial Cardiomyopathy: An Unexplored Limb of Virchow's Triad for AF Stroke Prophylaxis

The most dreaded complication of atrial fibrillation is stroke, and 70–80% of patients with AF-related stroke die or become disabled. The mechanisms of thromboembolism in AF are multifactorial, with evidence demonstrating that all three criteria of Virchow's triad are satisfied in AF: abnormal stasis of blood, endothelial damage, and hypercoagulability. Mechanistic insights into the latter two limbs have resulted in effective stroke prophylactic therapies (left atrial appendage occlusion and oral anticoagulants); however, despite these advances, there remains an excess of stroke in the AF population that may be due, in part, to a lack of mechanistic understanding of atrial hypocontractility resulting in abnormal stasis of blood within the atrium. These observations support the emerging concept of atrial cardiomyopathy as a cause of stroke. In this Review, we evaluate molecular, translational, and clinical evidence for atrial cardiomyopathy as a cause for stroke from AF, and present a rationale for further investigation of this largely unaddressed limb of Virchow's triad in AF.