Augmentation of Pulmonary Vein Backflow Velocity during Left Atrial Contraction: A Novel Phenomenon Responsible for Progression of Atrial Fibrillation in Hypertensive Patients

Echocardiographic assessment of left atrial appendage morphology and function-an expert proposal by the German Working Group of Cardiovascular Ultrasound

The left atrial appendage is a blind ending cardiac structure prone to blood stasis due to its morphology. This structure is a preferred region of thrombogenesis in relation to reduced myocardial contractility of the atrial wall. Blood stasis occurs primarily in low flow conditions. One of the tasks of echocardiography is the analysis of morphology and function of the left atrial appendage. The detection of thrombi by echocardiography is difficult and must be carried out thoroughly and carefully to avoid potential complications-especially in the context of rhythm control. The assessment of thromboembolic risk, especially in patients with unknown and presumed atrial fibrillation is a second challenge by characterizing atrial function and flow conditions in the left atrial appendage. Thus, this proposal focuses on the obvious problems of echocardiography when assessing left atrial appendage and the role of this method in planning a potential interventional closure of left atrial appendage.

Comprehensive left atrial flow component analysis reveals abnormal flow patterns in paroxysmal atrial fibrillation

Left atrial (LA) blood flow plays an important role in diseases such as atrial fibrillation (AF) and atrial cardiomyopathy since alterations in the blood flow might lead to thrombus formation and stroke. Using traditional techniques, such as echocardiography, atrial flow velocities can be measured at the pulmonary veins and the mitral valve, but a comprehensive understanding of the three-dimensional atrial flow field is missing. Previously, ventricular flow has been analyzed using flow component analysis, revealing new insights into ventricular flow and function. Thus, the aim of this project was to develop a comprehensive flow component analysis method for the LA and explore its utility in 21 patients with paroxysmal atrial fibrillation compared with a control group of 8 participants. The flow field was derived from time-resolved CT acquired during sinus rhythm using computational fluid dynamics. Flow components were computed from particle tracking. We identified six atrial flow components: conduit, reservoir, delayed ejection, retained inflow, residual volume, and pulmonary vein backflow. It was shown that conduit flow, defined as blood entering and leaving the LA within the same diastolic phase, exists in most subjects. Although the volume of conduit and reservoir is similar in patients with paroxysmal AF in sinus rhythm and controls, the volume of the other components is increased in paroxysmal AF. Comprehensive quantification of LA flow using flow component analysis makes atrial blood flow quantifiable, thus facilitating investigation of mechanisms underlying atrial dysfunction and can increase understanding of atrial blood flow in disease progression and stroke risk.NEW & NOTEWORTHY We developed a new comprehensive approach to atrial blood component analysis that includes both conduit flow and residual volume and compared the flow components of atrial fibrillation (AF) patients in sinus rhythm with controls. Conduit and reservoir flow were similar between the groups, whereas components with longer residence time in the left atrium were increased in the AF group. This could add to the pathophysiological understanding of atrial diseases and possibly clinical management.

Reduction in atrial and pulmonary vein stretch as a therapeutic target for prevention of atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with increased mortality. Heart failure, hypertension, valvular disease, and obstructive sleep apnea are risk factors for incident AF. A common characteristic of these diseases is that they increase atrial wall stretch. Multiple experimental studies confirm a proarrhythmic effect of atrial stretch. Conversely, a reduction in stretch is antiarrhythmic. A therapeutic target for AF, therefore, lies in local reduction of atrial stretch. This review focuses on atrial stretch and its clinical associations in patients with AF and its downstream effects on electrophysiology. We discuss the possible application of targeted atrial stretch reduction in AF prevention. We conclude that a reduction in local atrial stretch should be considered an essential element in rhythm control.

Pulmonary Vein Enlargement as an Independent Predictor for New-Onset Atrial Fibrillation

Pulmonary vein (PV) enlargement is associated with atrial fibrillation (AF). However, the predictive value of PV volume for new-onset AF has not been determined. We retrospectively assessed and enrolled non-AF subjects who underwent echocardiography and cardiac CT angiography (CCTA) around the same time and evaluated the development of AF longitudinally. PV volume was assessed by estimating the three-dimensional CCTA-derived mid-diastolic PV volume from the ostium to tertiary branches. Overall, 1105 subjects were enrolled. Among them, 29 developed AF during a mean follow-up of 4.28 ± 3.08 years after baseline CCTA and echocardiography. The AF group had a higher proportion of older aged subjects, a higher ratio of early mitral flow velocity (E) to early mitral annular tissue velocity (Em), higher Em, and larger left atrial (LAVI) and PV (PVVI) volume indices. PVVI was independently associated with male sex, left ventricular dimension, E/Em and LAVI. AF incidence increased markedly across each baseline PVVI tertile (2.2%, 5.1%, and 10.8%). In the multivariate Cox model, increased PVVI was independently associated with new-onset AF (hazard ratio (HR) = 5.401, 4.931–6.193, p = 0.007). Based on the analysis of multimodal cardiac imaging, our results provide mechanistic insights into PV remodeling and its potential role as a link between diastolic dysfunction and developing AF.

Tissue Doppler imaging of the atrial lateral wall: Correlation with atrial strain rate and parameters of diastolic function

OBJECTIVE

To evaluate the velocity profile of the lateral wall of the left atrium (LA) using pulsed-wave color tissue Doppler imaging (TDI) on line and its correlation with two-dimensional strain rate imaging (SRI) by speckle tracking, of equal segments and phases, and other parameters of diastolic function in a population of individuals without known cardiovascular disease.

MATERIALS AND METHODS

A total of 91 adults aged 18-74 years, without cardiovascular history, hypertension, diabetes, dyslipidemia or obesity, were evaluated. A Doppler echocardiogram was performed. The lateral wall of the LA was divided subjectively into three portions, the atrial roof was excluded; the peak velocities of the basal and midportions, and their average, were measured with pulsed-wave TDI on line and SRI. Using both techniques, a first positive wave (S'la and SRS-reservoir phase) and two negative waves (E'la and SRE-conduit phase-and A'la and SRA-atrial systole-respectively) were obtained. E'la/A'la ratio and SRE/SRA ratio were analyzed.

RESULTS

The median age was 42 years, and 54.9% of the subjects were female. S'la presented moderate correlation with S' lateral mitral annulus. Both E'la and the E'la/A'la relationships showed moderate to good correlation with various diastolic dysfunction parameters evaluated and SRI. A'la did not present a statistically significant correlation with any of the variables evaluated.

CONCLUSION

Evaluation of the lateral wall of the LA by pulsed-wave color TDI on line is feasible in the vast majority of patients. In the conduit phase, E'la and the E'la/A'la relationship showed correlation with the parameters that evaluate diastolic function and SRI.

Anticoagulation Stability Depends on CHADS2 Score and Hepatorenal Function in Warfarin-treated Patients, Including Those with Atrial Fibrillation

AIM

Although warfarin remains important despite the widespread use of nonvitamin K antagonist oral anticoagulants (NOACs), to date, the reality of warfarin use in the "NOACs era" is unclear. This multicenter observational study aimed to clarify the key factors contributing to warfarin treatment stability.

METHODS

The practical use of warfarin, stability of warfarin therapy, and factors contributing to this stability were investigated in community-based hospitals through a real-world study. Clinical data were retrospectively extracted from the medical records of warfarin-treated Japanese patients (age, 71.3±5.5 years) with atrial fibrillation (AF), prosthetic heart valve, or other concerns requiring anticoagulation. Treatment stability was considered as time in therapeutic range of international normalized ratio of prothrombin time (TTR: %). The factors contributing to TTR were investigated, including CHADS₂ score components.

RESULTS

Mean CHADS₂ score was highest (1.38±0.88, p＜0.001), and most CHADS₂ score components in addition to hepatorenal dysfunction were factors contributing to the low TTR in patients with AF (n=176). The similarity was found in overall patients who were prescribed warfarin (n= 518). TTR decreased according to the CHADS₂ score component accumulation. Gender, dose and prescription interval of warfarin, and co-administration of antiplatelet agents did not correlate with the low TTR.

CONCLUSIONS

This retrospective study demonstrated that the CHADS₂ score component accumulation and hepatorenal dysfunction are factors significantly contributing to the low TTR, which is indicative of poor warfarin treatment stability, in patients such as those with AF.

Renin-angiotensin system inhibitors prevent the recurrence of atrial fibrillation: a meta-analysis of randomized controlled trials

OBJECTIVE

This study was designed to assess whether angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) could prevent the recurrence of atrial fibrillation (AF).

METHODS

A systemic literature search of PubMed, EMBASE, and Cochrane Controlled Trials Register till 2012 was performed to identify randomized controlled trials involving the prevention of recurrence of AF with renin-angiotensin system blockade therapy. Subgroup analysis and meta-regression were performed. Publication bias was checked through funnel plot and Egger's test.

RESULTS

Twenty-one randomized controlled trials including 13,184 patients with AF were identified. Overall, the recurrence of AF was significantly reduced in patients using ACEI/ARBs [odds ratio (OR), 0.43; 95% confidence interval (CI), 0.32-0.56; P < 0.00001], especially both in irbesartan subgroup (OR, 0.38; 95% CI, 0.21-0.68; P = 0.001) and in patients receiving antiarrhythmic drug (AAD) (OR, 0.37; 95% CI, 0.29-0.48; P < 0.00001), and there was no significant difference between ACEIs and ARBs (ACEIs: OR, 0.42; 95% CI, 0.31-0.57 and ARBs: OR, 0.42; 95% CI, 0.31-0.57). Moreover, it was found that the benefits of ACEI/ARBs revealed positive correlation to systolic blood pressure (regression coefficient: -0.0700257, P = 0.000) in no-AAD users.

CONCLUSIONS

ACEI/ARBs are effective on the secondary prevention of AF, especially in patients receiving AAD and suffering from hypertension.

Left atrial function: physiology, assessment, and clinical implications

The interest in the left atrium (LA) has resurged over the recent years. In the early 1980s, multiple studies were conducted to determine the normal values of LA size. Over the past decade, LA size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes, including major public health problems such as atrial fibrillation, heart failure, stroke, and death. More recently, functional assessment of the LA has been shown to be, at least as, if not more robust, a marker of cardiovascular outcomes. Current available data suggest that the combined evaluation of LA size and LA function will augment prognostication. The aim of this review is to provide a critical appraisal of current echocardiographic techniques for the assessment of LA function and the implications of such assessment for prediction and disease prevention.

Hypertension and atrial fibrillation

Atrial fibrillation (AF) is an emerging public health problem. The most important risk factor for developing chronic AF is uncontrolled hypertension. Uncontrolled hypertension promotes the initiation and perpetuation of AF through atrial remodeling. Experimental evidence has demonstrated the important role of the renin-angiotensin system in atrial remodeling. Retrospective analysis of several large clinical trials and small prospective trials suggests the beneficial role of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in preventing the onset and recurrence of AF in different populations. Several large prospective trials with longer follow-up periods are in progress. These trials may provide definitive evidence for the use of these agents in the prevention of AF.

The role of pulmonary veins in atrial fibrillation: a complex yet simple story

Atrial fibrillation (AF) is the most common cardiac arrhythmia, with increased incidence among the elderly population. The concept that ectopic activity in pulmonary veins (PVs) could be responsible for triggering AF has been put forward, and the inter-relationship between PVs and left atrium has been the subject of many anatomical and physiological investigations. Variable configuration of action potentials among various PV cardiomyocytes has been reported. PV myocytes were shown to have a higher resting membrane potential and a lower action potential amplitude and duration than the left atrium. Much evidence has accumulated to indicate that spontaneous depolarization and/or re-entry from PVs could be the mode by which AF is initiated and/or sustained. Attempts have been made to link AF in certain pathophysiological states, notably, congestive heart failure, valvular disease and hyperthyroidism to PVs. There has been evidence to suggest that an increase in PV diameter may be the trigger for initiating AF. However, there is limited clinical knowledge available on the nature of the antiarrhythmic drugs that act upon PVs to alleviate AF. Most drugs currently employed are the standard agents generally utilized for the treatment of AF. Radiofrequency ablation (RFA) of the PVs and its isolation from the left atrium has become a major curative measure of AF. It is also possible that pharmacotherapy may be more effective or provide extra benefit to patients after a RFA procedure. The trend of the clinical evidence seems to suggest that a hybrid treatment may be beneficial in some population of patients.

Pulmonary vein contraction: characterization of dynamic changes in pulmonary vein morphology using multiphase multislice computed tomography scanning

BACKGROUND

The presence and extent of contraction within the pulmonary veins (PVs) have not been defined clearly.

OBJECTIVE

The purpose of this study was to determine whether PV contraction exists and can be visualized using multislice computed tomography (MSCT) scanning as this may indicate that this modality may be useful for monitoring patients after PV isolation procedures.

METHODS

Analysis was performed on 29 patients (mean age 57.5 +/- 12 years) undergoing MSCT for suspected coronary artery disease without structural heart disease or left atrial anatomical variants. Multiplane reconstructions were used to measure PV diameters at 0, 5, 10, and 15 mm from the ostium in two phases (maximum and minimum size). The ejection fractions of three 5-mm segments were calculated for each PV.

RESULTS

Right-sided and left-sided PV contraction and maximal atrial contraction occurred at a median of 85% and 95% of the cardiac cycle, respectively. The temporal concordance of minimal PV volume during peak atrial contraction indicated that the PV volume changes are secondary to active contraction rather than passive reflux and PV distension. The ejection fractions were highest in the superior veins: right superior PV (36.7%, 27.8%, and 16%, respectively, for the three segments from proximal to distal) and left superior PV (26.9%, 21.3%, and 12.1%), in comparison with the right inferior PV (21.1%, 6.6%, and -0.7%) and left inferior PV (15%, 9.3%, and 7.6%).

CONCLUSION

Volume changes related to active PV contraction occur extending up to 15 mm into the veins, and this effect is most pronounced in the superior veins.

Relationship between amiodarone-induced subclinical lung toxicity and Th1/Th2 balance

BACKGROUND

Although amiodarone is a potent antiarrhythmic agent, its clinical use is limited by serious lung toxicity. This study investigated the mechanisms of amiodarone-induced lung toxicity from an immunological perspective. Because interferon gamma (IFN-gamma: Th1 cytokine) inhibits pulmonary fibroblast proliferation whereas interleukin-4 (IL-4: Th2 cytokine) augments fibroblast growth and collagen production, we hypothesized that amiodarone lung toxicity is related to Th1/Th2 balance.

METHODS

Twenty-six consecutive Japanese patients with ventricular arrhythmias treated with amiodarone were enrolled in this study and were divided into two groups. Group A contained patients demonstrating amiodarone lung toxicity diagnosed by chest X-ray, KL-6 or D(LCO) (n=6), whereas group B included patients treated without any adverse effects (n=20). Th1/Th2 balance was investigated by the ratio of IFN-gamma and IL-4 produced by activated peripheral CD4(+) T cells.

RESULTS

Clinical baseline characteristics prior to oral amiodarone did not show any differences between group A and group B except for D(LCO) (82.0+/-5.2% vs. 90.8+/-9.0%, p=0.032) and Th1/Th2 balance (7.98+/-1.68 vs. 13.34+/-5.10, p=0.020). This balance was not altered three months after withdrawal of amiodarone in group A and under continued treatment in group B, suggesting patient-specific rather than amiodarone-induced. After starting amiodarone, serum concentration of desethylamiodarone was greater in group A than in group B (p=0.009) and was inversely proportional to Th1/Th2 ratio (p=0.013). Multilogistic regression analysis indicated that Th1/Th2 balance was the most powerful indicator of amiodarone lung toxicity (p=0.046, odds ratio of 0.424).

CONCLUSIONS

Although large cohort is required, the present study indicates that Th1/Th2 balance may influence amiodarone metabolism and may be a powerful indicator of amiodarone-induced subclinical lung toxicity at least in Japanese.