Targeting the renin-angiotensin-aldosterone-system in atrial fibrillation: a shift from electrical to structural therapy?

The prothrombotic state in atrial fibrillation: pathophysiological and management implications

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia and is associated with significant morbidity and mortality. There is plenty of evidence available to support the presence of a prothrombotic or hypercoagulable state in AF, but the contributory factors are multifactorial and cannot simply be explained by blood stasis. Abnormal changes in atrial wall (anatomical and structural, as ‘vessel wall abnormalities’), the presence of spontaneous echo contrast to signify abnormal changes in flow and stasis (‘flow abnormalities’), and abnormal changes in coagulation, platelet, and other pathophysiologic pathways (‘abnormalities of blood constituents’) are well documented in AF. The presence of these components therefore fulfils Virchow’s triad for thrombogenesis. In this review, we present an overview of the established and professed pathophysiological mechanisms for thrombogenesis in AF and its management implications.

Atrial Fibrillation and Stroke: A Neurologic Perspective

Atrial fibrillation (AF) is the most common supraventricular arrhythmia in the United States. The incidence and prevalence of AF are increasing as the population ages and associated risk factors become more prevalent. Stroke is the most severe complication of AF. Various risk stratification schemes to guide therapy and the associated risk of bleeding are described. AF is also associated with cognitive decline, which may be secondary to recurrent microemboli; microbleeds secondary to anticoagulation therapy, or progression of vascular risk factors associated with AF. Prolonged monitoring can be performed to detect AF in patients with cryptogenic stroke.

Indexing cardiac parameters in echocardiographic practice: do estimates depend on how weight and height have been assessed? A study on left atrial dilatation

We examined the difference between self-reported and measured height and weight in detecting echocardiographic left atrial dilatation (LAD), as defined by LA diameter indexed to body size parameters in an outpatient population referred to echocardiographic laboratories for routine examination. LAD was defined by 2 criteria: (1) LA diameter indexed to height greater than 24 mm/m; (2) LA diameter indexed to body surface area greater than 23 mm/m(2). Prevalence of LAD was calculated by indexing LA diameter to both self-reported and measured anthropometric values. In the whole population, LAD tended to be underestimated when LA diameter was indexed to self-reported compared with measured values, by 3.6% according to criterion 1 (26.4% versus 30.0%, P < .001) and by 0.6% according to criterion 2 (21.1% versus 21.6%, P = not significant). The difference between LAD estimates was more pronounced in older than in younger patients, either by criterion 1 (6.4% versus 1.6 %, P < .001) or by criterion 2 (2.1% versus 0.1%, P < .001). The error is related to demographic characteristics of patients and is more pronounced when LA diameter is normalized to height.

Chronic heart failure and the substrate for atrial fibrillation

AIMS

We sought to define the underlying mechanisms for atrial fibrillation (AF) during chronic heart failure (HF).

METHODS AND RESULTS

Preliminary studies showed that 4 months of HF resulted in irreversible systolic dysfunction (n = 9) and a substrate for sustained inducible AF (>3 months, n = 3). We used a chronic (4-month) canine model of tachypacing-induced HF (n = 10) to assess atrial electrophysiological remodelling, relative to controls (n = 5). Left ventricular fractional shortening was reduced from 37.2 +/- 0.83 to 13.44 +/- 2.63% (P < 0.05). Left atrial (LA) contractility (fractional area change) was reduced from 34.9 +/- 7.9 to 27.9 +/- 4.23% (P < 0.05). Action potential durations (APDs) at 50 and 90% repolarization were shortened by approximately 60 and 40%, respectively, during HF (P < 0.05). HF-induced atrial remodelling included increased fibrosis, increased I(to), and decreased I(K1), I(Kur), and I(Ks) (P < 0.05). HF induced increases in LA Kv channel interacting protein 2 (P < 0.05), no change in Kv4.3, Kv1.5, or Kir2.3, and reduced Kir2.1 (P < 0.05). When I(Ca-L) was elicited by action potential (AP) clamp, HF APs reduced the integral of I(Ca) in control myocytes, with a larger reduction in HF myocytes (P < 0.05). I(CaL) measured with standard voltage clamp was unchanged by HF. Incubation of myocytes with N-acetylcysteine (a glutathione precursor) attenuated HF-induced electrophysiological alterations. LA angiotensin-1 receptor expression was increased in HF.

CONCLUSION

Chronic HF causes alterations in ion channel expression and ion currents, resulting in attenuation of the APD and atrial contractility and a substrate for persistent AF.

Does treatment of hypertension decrease the incidence of atrial fibrillation and cardioembolic stroke?

Hypertension is the most common disease affecting humans. Statistical surveys indicate that approximately one billion individuals worldwide suffer from this serious condition. The spotlight of the present review is on the cardiac involvement in patients with hypertension and especially on the possibility that treatment of increased blood pressure may abolish the incidence of cardiac arrhythmia and particularly atrial fibrillation. Modern therapeutic approach based on the electrical and structural remodeling process in the hypertensive heart with a consequent administration of ACE inhibitors and AT1 receptor blockers represent new and more efficient option compared to other antihypertensive drugs, such as calcium channel blockers, beta-blockers and thiazide-type diuretics and might be useful in the prevention of atrial fibrillation and incidence of stroke.

Mechanisms of thrombogenesis in atrial fibrillation: Virchow's triad revisited

Atrial fibrillation is the most common sustained cardiac arrhythmia, which is associated with a high risk of stroke and thromboembolism. Increasing evidence suggests that the thrombogenic tendency in atrial fibrillation is related to several underlying pathophysiological mechanisms. Abnormal changes in flow are evident by stasis in the left atrium, and seen as spontaneous echocontrast. Abnormal changes in vessel walls-essentially, anatomical and structural defects-include progressive atrial dilatation, endocardial denudation, and oedematous or fibroelastic infiltration of the extracellular matrix. Additionally, abnormal changes in blood constituents are well described, and include haemostatic and platelet activation, as well as inflammation and growth factor changes. These changes result in the fulfilment of Virchow's triad for thrombogenesis, and accord with a prothrombotic or hypercoagulable state in this arrhythmia. In this Review, we present an overview of the established and purported mechanisms for thrombogenesis in atrial fibrillation.

Aldosterone synthase gene polymorphism as a determinant of atrial fibrillation in patients with heart failure

We analyzed the possible association between aldosterone synthase (CYP11B2) T-344C polymorphism, which is associated with increased aldosterone activity, and the prevalence of atrial fibrillation (AF) in 196 consecutive patients who had symptomatic systolic heart failure (HF; left ventricular ejection fraction <40%) for > or =3 months before recruitment. Genomic DNA was extracted from peripheral blood leukocytes using a standard protocol. Subjects were genotyped for the CYP11B2 polymorphism using the polymerase chain reaction/restriction fragment length polymorphism approach. AF was present in 63 patients (33%) with HF. We found the -344 CC genotype to be a strong independent marker for AF. Almost 1/2 (45%) of patients with this genotype had AF compared with 1/4 (27%) with -344 TT and TC genotypes (p = 0.01). A multivariate stepwise logistic regression model that included age, gender, New York Heart Association class, CYP11B2 -344CC genotype, and echocardiographic measurements of left ventricular ejection fraction, left atrial dimension, left ventricular end-diastolic diameter, and mitral regurgitation severity showed that the CYP11B2 CC genotype (adjusted for age and left atrial size) was an independent predictor of AF (adjusted odds ratio 2.35, 95% confidence interval 1.57 to 3.51, p = 0.03). In conclusion, CYP11B2 T-344C promoter polymorphism predisposes to clinical AF in patients with HF.

Angiotensin II receptor blockers and cardiovascular protection: focus on left ventricular hypertrophy regression and atrial fibrillation prevention

Left ventricular hypertrophy (LVH) and atrial fibrillation (AF) are strong predictors of cardiovascular (CV) morbidity and mortality, independently of blood pressure levels and other modifiable and nonmodifiable risk factors. The actions of circulating and tissue angiotensin II, mediated by AT1 receptors, play an important role in the development of a wide spectrum of cardiovascular alterations, including LVH, atrial enlargement and AF. Growing experimental and clinical evidence suggests that antihypertensive drugs may exert different effects on LVH regression and new onset AF in the setting of arterial hypertension. Since a number of large and adequately designed studies have found angiotensin II receptor blockers (ARBs) to be more effective in reducing LVH than beta-blockers and data are also available showing their effectiveness in preventing new or recurrent AF, it is reasonable to consider this class of drugs among first line therapies in patients with hypertension and LVH (a very high risk phenotype predisposing to AF) and as adjunctive therapy to antiarrhythmic agents in patients undergoing pharmacological or electrical cardioversion of AF.

Angiotensin converting enzyme inhibitor and angiotensin receptor blockade use in relation to outcomes in anticoagulated patients with atrial fibrillation

BACKGROUND

The renin-angiotensin-aldosterone-system (RAAS) plays an important role in atrial fibrillation (AF). Evidence shows that blocking the RAAS with angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has a definite role in preventing new onset AF and in maintaining sinus rhythm in recurrent AF. Our aim was to determine if ACEI/ARB treatment was associated with clinical outcomes [stroke/systemic embolic events (SEE), mortality] in a controlled, anticoagulated AF population.

METHODS

An ancillary retrospective cross-sectional and longitudinal analysis of participants in the Stroke Prevention using an ORal Thrombin Inhibitor in AF (SPORTIF) III and V trials, in relation to use (or nonuse) of ACEI/ARBs.

RESULTS

Rates of stroke/SEEs, mortality or major bleeding were no different between users and nonusers in the whole cohort, or in relation to the presence/absence of hypertension, coronary artery disease and previous stroke/transient ischaemic attack, nor amongst those aged <75 years. Patients aged > or = 75 years taking ACEIs or ARBs had lower mortality (HR 0.71, 95% CI 0.52-0.95), but no significant influence on other end-points was noted. Diabetics and those with left ventricular dysfunction on ximelagatran had a higher odds ratio of abnormal liver enzyme levels. There was no apparent benefit of ACEIs or ARBs on other event rates.

CONCLUSIONS

This analysis from two large randomized trials of anticoagulation has not demonstrated a significant benefit of ACEI or ARB use amongst AF patients, except amongst elderly subjects.

Pharmacotherapy changes following pacemaker implantation in patients with bradycardia-tachycardia syndrome

The management of bradycardia-tachycardia syndrome (BTS) includes bradycardia and tachyarrhythmia therapy. At present, the treatment for symptomatic bradycardia in BTS patients is permanent cardiac pacing. The pharmacological treatment of atrial tachyarrhythmias comprises of rhythm and rate control, and prevention of thromboembolism. Patients with BTS often require both pacemaker and drug therapy. This article reviews the interactions of pacing and drug therapies in BTS. Drugs that alter cardiac electrophysiological properties may influence pacemaker indications, pacing mode selection, efficacy of pacing algorithms and pacing performance. Pacing by preventing drug-induced bradycardia increases the safety of pharmacotherapy and, thus, allows the intensification of those treatments. Pacing therapy and antiarrhythmic drugs used together as a hybrid therapy have a synergistic effect in the prevention of atrial tachyarrhythmias. Atrial-based pacing may reduce atrial tachyarrhythmia burden, allowing reduction of rhythm and rate control. Contemporary pacemakers' memory functions may help guide rhythm and rate control, as well as anticoagulation pharmacotherapy.