EVALUATION OF PULMONARY VENOUS FLOW BY TRANSESOPHAGEAL ECHOCARDIOGRAPHY IN SUBJECTS WITH A NORMAL HEART - COMPARISON WITH TRANSTHORACIC ECHOCARDIOGRAPHY

Nineteen normal subjects and five patients with atrial fibrillation underwent transesophageal and transthoracic echocardiographic studies to evaluate the normal pulmonary venous flow pattern, compare right and left pulmonary venous flow and assess the effect of sample volume location on pulmonary venous flow velocities. Best quality tracings were obtained by transesophageal echocardiography. Anterograde flow during systole and diastole was observed in all patients by both techniques. Reversed flow during atrial contraction was observed with transesophageal echocardiography in 18 of the 19 subjects in normal sinus rhythm, but in only 7 subjects with transthoracic echocardiography. Two forward peaks during ventricular systole were clearly identified in 14 subjects (73%) with transesophageal echocardiography, but in none with the transthoracic technique. The early systolic wave immediately followed the reversed flow during atrial contraction and was strongly related to the timing of atrial contraction (r = 0.78; p < 0.001), but not to the timing of ventricular contraction, and appeared to be secondary to atrial relaxation. Conversely, the late systolic wave was temporally related to ventricular ejection (r = 0.66; p < 0.001), peaking 100 ms before the end of the aortic valve closure and was unrelated to atrial contraction time. Quantitatively, significantly higher peak systolic flow velocities were obtained in the left upper pulmonary vein compared with the right upper pulmonary vein (60 +/- 17 vs. 52 +/- 15 cm/s; p < 0.05) and by transesophageal echocardiography compared with transthoracic studies (60 +/- 17 vs. 50 +/- 14 cm/s; p < 0.05). Increasing depth of interrogation beyond 1 cm from the vein orifice resulted in a significant decrease in the number of interpretable tracings. The effect was minimal on systolic flow velocities, but diastolic flow velocities decreased significantly at 2 cm (44 +/- 9 vs. 36 +/- 3 cm/s; p < 0.05). Thus, four distinct phases can be distinguished in normal pulmonary venous flow by transesophageal echocardiography: two anterograde flow waves during ventricular systole generated by atrial relaxation and ventricular contraction, respectively, an anterograde flow wave during diastole and one reversed (retrograde) flow wave during atrial contraction. Significantly better quality tracings with distinctive phasic peaks are identified by transesophageal echocardiography. A depth of 0.5 to 1 cm provides the optimal location for interpretable velocities and stable recordings.