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(Chest. 2000;117:1546-1550.)
© 2000 American College of Chest Physicians

Effect of Atrial Fibrillation on Pulmonary Venous Flow Patterns Assessed by Doppler Transesophageal Echocardiography*

Ting-Hsing Chao, MD; Liang-Miin Tsai, MD; Wei-Chuan Tsai, MD; Yi-Heng Li, MD; Li-Jen Lin, MD and Jyh-Hong Chen, MD, PhD

* From the Section of Cardiology, Department of Internal Medicine, National Cheng Kung University Hospital, Tainan, Taiwan.

Correspondence to: Liang-Miin Tsai, MD, Professor of Medicine, Section of Cardiology, Department of Internal Medicine, National Cheng Kung University Medical College and Hospital, 138 Sheng-Li Road, Tainan 704, Taiwan


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: To investigate the effect of atrial fibrillation (AF) on pulmonary venous flow (PVF) patterns in a cohort with nonrheumatic AF.

Design and settings: A prospective and controlled study undertaken at a tertiary referral medical center.

Patients and measurements: The echocardiographic parameters of left superior PVF as assessed by Doppler transesophageal echocardiography in 40 patients with chronic AF (group 1) were compared to those of 33 volunteers with sinus rhythm (group 2) and well-matched baseline characteristics.

Results: All group 1 patients presented with single systolic forward flow (SFF) patterns. In contrast, single and double SFF patterns were found equally in group 2. With regard to reverse flow (RF), most group 1 patients (33 of 40) had an early systolic RF and none had atrial RF; however, most group 2 subjects (29 of 33) had an atrial RF. Some of the group 1 patients (17%) had a late systolic RF in the absence of significant mitral regurgitation. In group 1, the SFF appeared later and disappeared earlier than in group 2. The mean systolic peak velocity and time-velocity integral (TVI) of the SFF were significantly lower in group 1 compared to group 2. The diastolic peak velocity and TVI were not significantly different between groups.

Conclusions: Our data indicate that AF independently and significantly affects the PVF and leads to characteristic flow patterns different from sinus rhythm. The presence of AF reduces SFF in addition to the absence of atrial RF. These changes in the flow patterns should be taken into account while interpreting the implications of PVF in the presence of AF.

Key Words: atrial fibrillation • pulmonary venous flow • transesophageal echocardiography


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The flow patterns of the pulmonary veins have been described in healthy1 2 3 and diseased hearts.4 5 Some Doppler echocardiography parameters of pulmonary venous flow (PVF) have been reported to be implicated in the detection of the presence of severe mitral regurgitation6 and in the estimation of the level of left ventricular end-diastolic pressure7 in patients with sinus rhythm. Although the PVF patterns in patients with chronic atrial fibrillation (AF) have been presented in a few studies,8 9 10 the effect of AF on the PVF is still poorly understood. Previous studies may have been limited by a heterogeneous population, small sample size, and less control. Recently, several factors have been reported to affect the PVF. These include age,11 12 left ventricular function,4 heart rate,2 13 14 respiration,2 12 and severity of mitral regurgitation.8 15 16 It is necessary to control these confounding factors when evaluating the PVF patterns with AF. The purpose of this study was to investigate the effect of AF on PVF under a well-controlled design.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Study Population
This study included a total of 40 patients with chronic nonrheumatic AF (group 1) and 33 volunteers with sinus rhythm and no major cardiovascular complications (group 2). In group 2, those with uncomplicated hypertension were not excluded. All patients in group 1 had an AF rhythm, which was found to persist over 30 days as documented by serial ECGs, and none had physical or echocardiographic evidence of rheumatic mitral stenosis or a prosthetic mitral valve. The underlying etiologies of AF were hypertension in 19 patients, coronary artery disease in 2 patients, hyperthyroidism in 2 patients, and lone AF in 17 patients. None of group 2 had a history of tachycardia or documented AF on ECGs. Patients who had contraindication of transesophageal echocardiography (TEE) or who could not tolerate this procedure were excluded. In addition, patients with poor TEE images or significant mitral regurgitation were also excluded. Informed consent was obtained from all study subjects before enrollment.

Echocardiograhy
Both transthoracic echocardiography and TEE studies were performed in all subjects. Transthoracic echocardiography was performed with a 2.0- or 2.5-MHz phased-array transducer and a commercially available ultrasound system (Sonos 1500; Hewlett-Packard; Andover, MA). Subjects were examined in the left lateral semirecumbent position during quiet respiration. M-mode echocardiographic measurements were made as recommended by the American Society of Echocardiography,17 and five consecutive beats were averaged. The left ventricular ejection fraction was calculated using the method described by Teichholz et al.18 Mitral regurgitation was evaluated and graded by color flow imaging.19 A grade of moderate or severe mitral regurgitation was considered significant. A 5-MHz multiplane probe (model 21364A; Hewlett-Packard) was used to perform TEE in the left lateral decubitus position. All subjects fasted for > 4 h before the TEE study. IV or IM sedation with diazepam (2.5 to 5 mg) and topical pharyngeal anesthesia with 2% lidocaine (Xylocaine) spray were administered before insertion of the transesophageal probe. Pulmonary veins were visualized by rotating and tilting the transducer far leftwards to the upper portion of the left atrium. PVF velocity profiles were obtained by pulsed-wave Doppler echocardiography with the sample volume placed in the left upper pulmonary vein, approximately 0.5- to 1-cm proximal to the entrance into the left atrium. The peak flow velocities and flow time-velocity integrals (TVIs) of the systolic forward flow (SFF), diastolic forward flow (DFF), and reverse flow (RF) were measured and averaged over five consecutive cardiac cycles during end expiration. The TVI of the biphasic SFF pattern was determined by calculating the whole systolic component of the forward flow, and the highest point of the SFF was chosen as the peak of the biphasic SFF. In addition, we also calculated the separate TVI of the early and late components of the SFF in normal subjects with the biphasic SFF pattern.

Statistical Analysis
Results were expressed as mean ± SD. All analyses were performed with a software program (SPSS for Windows; SPSS; Chicago, IL). Continuous variables were compared with an unpaired Student’s t test, and categorical variables were compared with a {chi}2 test, with Yates correction between groups. A significance level of p <= 0.05 by two-tailed analysis was used in all tests.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
The underlying clinical and echocardiographic characteristics in both groups are shown in Table 1 . There were no significant differences between groups regarding age, sex, left ventricular end-diastolic and end-systolic diameters, ejection fraction, and the presence of hypertension, mitral regurgitation, or tachycardia (> 100 beats/min).


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  		Table 1.. Clinical and Echocardiographic Characteristics in Both Groups*

 
PVF Patterns
The PVF patterns of the two groups are listed in Table 2 , and examples are illustrated in Figure 1 . The forward flow consisted of two components, including SFF (which appeared as a monophasic [single] or biphasic [double] wave) at systole and DFF at diastole. The end of the SFF was almost always accompanied with the beginning of the DFF. All of group 1 presented single SFF patterns. In contrast, single and double SFF patterns were found in group 2 with almost equal distributions (17 single and 16 double). RF waves appeared in both groups. The onset of the RF that appeared just after the end of the DFF was correlated with P wave on the ECG, suggestive of atrial contraction. Such an RF was called atrial RF. Early systolic RF occurred in the early stage of systole and just after the peak of the R wave on the ECG, whereas late systolic RF appeared in the late half of systole. In group 2, most had atrial RF (88%), and the remainder of the group had early systolic RF (12%). In contrast, none of the patients with AF had atrial RF, and all of them had systolic RF (83% at early systole and 17% at late systole).


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  		Table 2.. Patterns of PVF in Both Groups*

 


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  		Figure 1.. The Doppler echocardiography flow patterns of the pulmonary vein showing biphasic SFF with atrial reversal in sinus rhythm (upper panel) and monophasic SFF with early systolic reversal in AF (lower panel). The cyclic changes of respiration (arrow) were recorded simultaneously. S = SFF (S1 = early component, S2 = late component); D = DFF; AR = atrial reversal; ESR = early systolic reversal.

 
Doppler Echocardiography Parameters of the PVF
The Doppler echocardiography parameters of the PVF are shown in Tables 3 , 4 . In control subjects with biphasic SFF, both peak velocity and TVI were larger in late SFF than early SFF. The peak velocity and TVI of the SFF were reduced markedly in group 1 compared to group 2; however, the DFF was not significantly different. The TVI of the SFF in group 1 was significantly less than that of the late SFF in control subjects who had biphasic SFF pattern (4.2 ± 2.5 cm vs 7.5 ± 2.9 cm; p < 0.001). In group 2, the peak velocity and TVI of the SFF were greater than those of the DFF. In contrast, inverse relations of these parameters were found in group 1. In group 1, the deceleration time and duration of the SFF were shorter, and the onset of SFF was delayed in comparison with those in group 2. With regard to the DFF, the deceleration time and duration were not significantly different between the two groups, but the onset of the DFF was earlier in group 2.


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  		Table 3.. Early and Late Peak Velocities and TVIs of SFF in Control Subjects With Biphasic SFF Pattern*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Since the advent of TEE, PVF patterns can be assessed easily and clearly.1 Blood flow in the pulmonary veins is inversely related to pressure events in the left atrium.20 21 In normal individuals with sinus rhythm, PVF patterns consist of a biphasic or triphasic forward flow wave and an atrial RF.22 23 Previous reports showed that early SFF is influenced by atrial relaxation, late SFF by downward displacement of mitral leaflets to the left ventricle during ventricle contraction, DFF by rapid filling during ventricle relaxation, and atrial RF by atrial contraction.22

Several clinical factors have been reported to affect the PVF patterns in normal or diseased hearts. First, the effect of old age is greater on SFF velocity than DFF velocity, and the amplitude of atrial RF is increased in the elderly.11 12 Second, in sinus tachycardia, the RF wave may disappear,2 the peak velocity ratio of SFF/DFF may increase,13 and the SFF and DFF will fuse.14 Third, spontaneous respiration has little effect on the PVF,2 12 but straining during the Valsalva maneuver markedly decreases the peak velocity and TVI of the SFF and DFF.2 Fourth, decreased mitral annular motion due to lower left ventricular ejection fraction in dilated cardiomyopathy reduces the SFF component.4 Fifth, mitral regurgitation may reduce the amplitude of SFF and contribute to the presence of late systolic RF.8 15 16 Finally, mitral stenosis may decrease the SFF component24 25 and prolong DFF.24 Our study uniquely identifies the actual and independent effect of AF on PVF by carefully controlling each of the above-mentioned confounding factors.

The PVF patterns in AF have been presented in a few studies8 9 10 ; however, the reported results are inconsistent. Castello et al8 reported that peak SFF velocities in patients with AF were not significantly reduced, as compared to those in sinus rhythm, whereas peak DFF velocities were significantly higher in AF. In contrast, Ren et al9 indicated that the SFF parameters were significantly different between those with sinus rhythm and AF patients.

In our study, the flow patterns of the pulmonary veins were significantly different between patients with AF and the normal control subjects. The loss of atrial RF and early SFF in all patients with AF is suggestive of the absence of the atrial contraction and relaxation, respectively. Accordingly, most of the SFF in AF originated from the contribution of downward displacement of mitral leaflets to the left ventricle at systole. In control subjects, the mean TVI of late SFF was higher than that of early SFF, suggesting that the contribution of the downward displacement of mitral leaflets was more than that of the atrial relaxation with regard to the SFF. The decreased TVI of SFF in patients with AF was probably due to the loss of the atrial relaxation, as well as the reduced amplitude of the downward displacement of mitral leaflets. The smaller TVI of SFF in AF patients compared to late systolic TVI in the control subjects suggests a decreased mitral movement in AF. A recent study reported that late SFF could also be caused by forward propagation of right ventricular pressure26 ; whether this mechanism could be affected by AF remains unknown. The peak velocity and TVI ratios of SFF/DFF were < 1.0 in patients with AF and > 1.0 in the control group. This discrepancy was primarily due to the differences of SFF. With regard to the atrial functions, our results suggest that the presence of AF may cause marked impairment of the atrial pumping and reservoir functions, but not the conduit function.

The end of SFF was always accompanied by the beginning of DFF in all echocardiography studies, suggesting that the end of the recoil of the mitral annulus toward the atrium coincided with the onset of transmitral filling.4 In patients with AF, the deceleration time of SFF was shorter, and the onset and peaking of DFF were earlier compared with control group. We postulate that the absence of the atrial contraction during the late stage of mitral filling in AF may increase the blood volume and, hence, create a higher pressure burden in the left atrial cavity during ventricular systole. This may lead to the reduced deceleration time of SFF and the early onset of DFF.

Systolic RF was present in all AF patients (83% with early and 17% with late systolic RF), but in only 12% of the normal control subjects (all with early systolic RF). The possible mechanisms for systolic RF might be that the mitral valve leaflets remain in a semi-open position during systole in humans with AF.27 Paraskevaidis et al10 observed that systolic RF appears in concordance with the abnormal motion of the mitral annulus toward the left atrium during early systole, due probably to the absence of atrial relaxation. In terms of late systolic RF, some studies have addressed the clinical importance of these flow patterns accounting for the existence of clinically significant mitral regurgitation.8 15 16 As observed in one report,28 we found some AF patients to have late systolic RF, and none of these patients had significant mitral regurgitation. Therefore, late systolic RF is not reliable in predicting severe mitral regurgitation in the presence of AF.

Several limitations should be mentioned. First, the number of our study subjects was not large enough to represent the general population of AF patients. Second, we evaluated only the flow patterns of the left superior pulmonary vein. Third, the intracardiac pressures were not measured; therefore, the implication of PVF on hemodynamics such as atrial pressure could only be postulated.

In conclusion, our results indicate that AF significantly affects the PVF and leads to characteristic flow patterns distinct from sinus rhythm. The absence of atrial contraction and relaxation contributes largely to the changes of PVF in AF. The clinical implications of PVF as reported in sinus rhythm should be interpreted cautiously when applied to patients with AF.


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  		Table 4.. The Doppler Echocardiography Parameters of PVF in Both Groups*

 

   Footnotes
 
Abbreviations: AF = atrial fibrillation; DFF = diastolic forward flow; PVF = pulmonary venous flow; RF = reverse flow; SFF = systolic forward flow; TEE = transesophageal echocardiography; TVI = time-velocity integral

These results have been presented in part at the Eighth Asian-Pacific Conference on Doppler and Echocardiography, Taipei, Taiwan, May 13–14, 1999.

Received for publication August 31, 1999. Accepted for publication January 25, 2000.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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