Effect of cardiac resynchronization therapy on left atrial appendage function and pulmonary venous flow pattern

Assessment of left atrial appendage function by echocardiography

The left atrial appendage (LAA) is considered not only to be the most frequent site of thrombus formation, but also to play a pivotal role in maintaining normal cardiac function. Transesophageal echocardiography (TEE) is widely used to assess LAA function. The LAA flow velocity has been used as a surrogate for LAA function, and it varies with multiple interrelated factors including age, hemodynamics, type of arrhythmia, and antiarrhythmic interventions. Relatively great importance of LAA function is involved with intraatrial thrombus formation and subsequent thromboembolism, and thus, understanding of characteristics and behaviors of the LAA under various clinical conditions may help determine strategies against atrial thrombosis. Also, techniques other than TEE-derived Doppler to assess LAA function, such as tissue Doppler imaging, have been proposed. In this review, we introduce clinical and echocardiographic correlates of LAA function, the LAA flow velocity in particular, its significance, and how to interpret functional patterns of the LAA each relevant to specific clinical settings.

Relationships between velocities of pulmonary venous flow and plasma concentrations of atrial natriuretic peptide in healthy dogs

OBJECTIVE

To investigate the relationship between velocities of pulmonary venous flow (PVF) and plasma concentrations of atrial natriuretic peptide (ANP) in healthy dogs.

ANIMALS

7 healthy Beagles.

PROCEDURES

Dogs were anesthetized, intubated, and positioned in left lateral recumbency. Lactated Ringer's solution was infused (200 mL/kg/h) for 60 minutes via a cephalic vein. Transmitral flow and PVF velocities were measured echocardiographically by use of the apical 4-chamber view. Pulmonary capillary wedge pressure (PCWP) and ANP concentrations were determined.

RESULTS

IV infusion significantly increased heart rate and PCWP. Similarly, the ANP concentration significantly increased from baseline (before infusion of lactated Ringer's solution) values. Transmitral flow velocities were significantly increased, although the ratio of velocity of the flow during early ventricular diastole (E wave) to velocity of the atrial flow (A wave; E:A ratio) was unchanged. Regarding the PVF velocities, forward flow during ventricular systole (S wave) and retrograde flow during atrial contraction were significantly increased, whereas velocity of the forward flow during ventricular diastole (D wave) was unchanged. Ratio of the velocity of the S wave to velocity of the D wave was increased significantly, and this ratio was significantly correlated with PCWP or ANP concentration. However, the E:A ratio was not correlated with PCWP or ANP concentration.

CONCLUSIONS AND CLINICAL RELEVANCE

PVF velocities were strongly correlated with PCWP and plasma ANP concentration in clinically normal dogs. Therefore, PVF velocities may serve as a sensitive indicator and provide additional information for monitoring acute preloading conditions and estimating atrial filling abnormalities in dogs.

Burden of atrial fibrillation after cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) may diminish atrial fibrillation (AF) burden in patients with chronic heart failure (HF). Each of 27 patients without permanent AF in whom CRT implantation was unsuccessful was paired with 2 active CRT patients-1 responder and 1 nonresponder-based on age, gender, cause of HF, and history of paroxysmal AF. Device-documented high atrial rates and mode-switching episodes were tabulated during a median follow-up of 386 days. CRT responders had significantly improved left ventricular (LV) ejection fraction and New York Heart Association functional class compared with nonresponders and controls. Left atrial dimension change was similar among the groups (+0.03 +/- 0.92 cm controls; -0.18 +/- 0.80 cm responders; -0.11 +/- 1.01 cm nonresponders) despite a significant reduction in mitral regurgitation in responders compared with nonresponders. There was no significant difference in AF burden between controls and patients who underewent CRT when indexed over time. Median AF-free follow-up was significantly longer in patients who underwent CRT without a history of AF (log-rank p = 0.04), but no differences were seen in the overall cohorts. In conclusion, despite inducing LV reverse remodeling and clinical improvement, CRT does not appear to decrease AF burden in responders compared with nonresponders or matched controls in whom CRT implantation failed. CRT may, however, delay onset of new AF.

Echocardiographic Assessment of Ventricular Asynchrony in Dilated Cardiomyopathy and Congenital Heart Disease: Tools and Hopes

Ventricular dyssynchrony is a relatively common problem in patients with heart failure, in particular those with wide QRS complex, and appears to have a deleterious effect on the natural history of heart failure, as it has been associated with increased mortality. Mechanistic studies, observational evaluations, and randomized trials have consistently demonstrated the beneficial effects of cardiac resynchronization therapy (CRT) in patients with moderate-to-severe chronic systolic heart failure and ventricular dyssynchrony who have failed optimal medical treatment. However, despite the promising results, it is estimated that in approximately 30% of patients undergoing CRT, the symptoms of heart failure do not improve or become even worse. One of the most important reasons for this failure is probably the lack of distinct mechanical dyssynchrony before implantation. A number of echocardiographic tools have been developed during the past 3 years for quantitative measurement of the severity of dyssynchrony before and after CRT. This review discusses the actual and potential role of different echocardiographic techniques in selection of patients and optimization of CRT and the value of some new clinical applications such as in congenital heart disease.