Understanding left atrial pressure: basic physiology, hemodynamics, and current echocardiographic assessment

Left atrial pressure (LAP) is a major determinant of pulmonary congestion and a key hemodynamic parameter in patients with heart failure and atrial fibrillation. LAP has traditionally been regarded as a surrogate of left ventricular (LV) filling pressure. However, growing evidence indicates that LAP reflects integrated interactions between left atrial (LA) mechanics, LV diastolic and systolic function, and extrinsic mechanical restraints throughout the cardiac cycle. Understanding the physiological basis of the LAP waveform provides important insights into the LA booster pump, reservoir, and conduit functions, as well as LA-LV interactions. Recent advances in echocardiography have expanded the noninvasive assessment of LAP beyond conventional Doppler indices. Contemporary approaches integrate the values of transmitral flow, mitral annular velocity, pulmonary venous flow, LA volume, and LA reservoir strain to provide a more comprehensive noninvasive assessment of LAP. In particular, LA reservoir strain has emerged as a promising marker of LAP and atrial mechanics. Additionally, exercise stress echocardiography and preload stress testing can reveal occult abnormalities in LAP responses that are not apparent at rest, particularly in patients with heart failure with preserved ejection fraction. Abnormal LAP also plays a central role in the pathophysiology of atrial fibrillation, atrial remodeling, and stiff LA physiology. This review summarizes the physiological determinants of LAP, the hemodynamic significance of the LAP waveform, and contemporary echocardiographic approaches for the assessment of LAP, and the impact of extrinsic mechanical restraints on LAP, with particular emphasis on the clinical relevance of LA-LV interactions in heart failure with preserved ejection fraction and atrial fibrillation.