Points
One of the important limitations in interpreting pulmonary venous flow is the difficulty in obtaining high-quality recordings suitable for measurements. This is especially true for Ar velocity, for which atrial contraction can create low-velocity wall motion artifacts that obscure the pulmonary flow velocity signal.
Sinus tachycardia and first-degree AV block often result in the start of atrial contraction occurring before diastolic mitral and pulmonary venous flow velocity has declined to the zero baseline. This increases the width of the mitral A-wave velocity and decreases that of the reversal in the pulmonary vein, making the Ar-A relationship difficult to interpret for assessing LV A-wave pressure increase.
With atrial fibrillation, the loss of atrial contraction and relaxation reduces pulmonary venous systolic flow regardless of filling pressures.
With a first-degree AV block of ≥300 ms, flow into the left atrium with its relaxation (S1) cannot be separated from later systolic flow (S2), or can even occur in diastole.