Vorhofsystole

Vorhofsystole, or atrial systole, is the contraction of the atrial myocardium that completes ventricular filling at the end of diastole. It follows atrial depolarization, typically visible as the P wave on an ECG, and occurs just before the ventricles begin their contraction.

Physiological role and timing

During late diastole the atria actively push a final bolus of blood into the ventricles, known as the atrial kick. This adds to passive ventricular filling and helps optimize preload. In a healthy heart, atrial systole contributes roughly 10–20% of left ventricular end-diastolic volume, but the contribution can be more important when ventricular compliance is reduced or diastolic function is impaired.

Clinical significance

Atrial systole is preserved in normal sinus rhythm but is absent or markedly reduced in atrial fibrillation and some other arrhythmias, leading to lower preload and potentially reduced cardiac output, especially when diastolic filling is limited. Conditions that increase dependence on atrial contraction, such as diastolic dysfunction or mitral stenosis, can make atrial systole more clinically relevant. Judging atrial contraction against a closed AV valve can also raise atrial and upstream venous pressures, contributing to symptoms like dyspnea.

Diagnosis and assessment

Electrocardiography correlates atrial systole with the P wave. Echocardiography assesses the timing and effectiveness of atrial contraction and its impact on ventricular filling. Jugular venous pressure tracing shows the a wave, reflecting active atrial contraction.

Overview

Vorhofsystole is a normal, integral phase of the cardiac cycle that enhances ventricular filling, with its importance varying according to ventricular compliance and rhythm.