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Ann Thorac Surg 1995;60:354-359
© 1995 The Society of Thoracic Surgeons
Departments of Thoracic Surgery, Yokkaichi Municipal Hospital, Yokkaichi, and Nagoya University School of Medicine, Nagoya, Japan
Accepted for publication February 20, 1995.
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentReferences |
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Methods. Left atrial function after Cox's maze operation performed concomitantly with a mitral valve operation was evaluated in 10 patients ranging in age from 38 to 67 years (mean age, 54 years). Seven patients who had had coronary artery bypass grafting served as the control group. Using transthoracic echocardiography, the ratio between the peak speed of the early filling wave and that of the atrial contraction wave (A/E ratio) and the atrial filling fraction (AFF) were determined from transmitral flow measurements. These two indices have been considered to represent the contribution of left atrial active contraction to ventricular filling.
Results. The A/E ratio and the AFF were significantly lower in the maze group (0.35 +/- 0.17 versus 0.97 +/- 0.28 [p < 0.01] and 17.6% +/- 8.8% versus 36.8% +/- 6.4% [p < 0.01], respectively). The A/E ratio and the AFF correlated inversely with age (r = -0.72, p < 0.05 and r = 0.76, p < 0.05, respectively) in the maze group. In an angiographic study, the mean left atrial maximal volume index in the maze group was approximately three times larger than that in the control group (117.5 +/- 24.3 mL/m2 versus 35.3 +/- 6.6 mL/m2 [p < 0.01]). The left atrial active emptying volume index was significantly smaller in patients in the maze group (7.2 +/- 2.5 mL/m2 versus 13.1 +/- 4.6 mL/m2 [p < 0.01]).
Conclusions. After the maze procedure performed concomitantly with a mitral valve operation in patients with a dilated left atrium, left atrial contraction is detectable but incomplete in the elderly.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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Atrial fibrillation (AF) is fairly common in patients with chronic mitral valve disease and a markedly dilated left atrium. These patients rarely return to sinus rhythm spontaneously even after a successful mitral valve operation [1]. They may continue to have palpitations and impaired left ventricular function caused by the loss of left atrial active transport function and an inadequate ventricular rate response.
The maze procedure, developed by Cox and associates [2, 3], has been used in patients undergoing a mitral valve operation. Restoration of normal sinus rhythm and atrial contraction in such patients has been reported by some groups [3--5]. If adequate atrial contraction is restored by adding the maze procedure to the mitral valve operation, postoperative cardiac function may be improved and the risk of thromboembolic events may be decreased. To determine whether this occurs, detailed characteristics of atrial function in patients who have undergone the maze operation concomitantly with a mitral valve surgical procedure must be elucidated. In this report, we analyzed left atrial function in such patients using Doppler echocardiography and cardiac catheterization.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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. There were no significant differences in age or body surface area between the two groups. All patients in the maze group had a history of chronic AF for at least 4 years and were in New York Heart Association class III. In the control group, all grafts were patent, and complete revascularization had been achieved.
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Postoperatively, all patients in the maze group returned to sinus rhythm with a normal P-R interval in 2 weeks. No patient required permanent pacemaker implantation.
Prophylactic antiarrhythmic drug therapy with pilsicanide hydrochloride, 75 mg/d, was started soon after the operation and continued until all studies had been performed in the maze group. In the control group, all patients were given 90 mg of diltiazem hydrochloride and 40 mg of isosorbide dinitrate orally every day.
Doppler Echocardiographic Study
Transthoracic echocardiographic studies were performed 2 to 5 months postoperatively in the maze group and 1 month postoperatively in the control group. Full recovery of cardiac performance requires at least 1 month even after only simple cardioversion in patients with chronic AF unassociated with cardiac valve disease [7]. Therefore, echocardiographic studies were performed later in the maze group than in the control group.
In addition to routine M-mode measurements of left ventricular function, the mitral inflow velocity was recorded with pulsed Doppler. Doppler sample volume was placed at the tip of the mitral valve leaflets as they opened or at the center of the mitral prosthesis, thereby obtaining an apical four-chamber view. Continuous-wave Doppler also was used in patients whose transmitral flow velocity exceeded the measurable limit of the pulsed Doppler system. Peak velocities of the early filling wave (E wave) and the atrial contraction wave (A wave) and the total time-velocity integral of transmitral flow during diastole were measured. The passive component and the atrial component of the time-velocity integral were measured using the method described by Kuo and associates [8].
Measurements from five Doppler tracings were averaged. To cancel out the difference in mitral valve area between patients, the A/E ratio (the velocity of the peak A wave divided by that of the E wave) and the atrial filling fraction (AFF) (atrial component of time-velocity integral divided by total time-velocity integral) were calculated. These indices have been used by several authors [8--11] to estimate the contribution of atrial contraction to ventricular filling. The A/E ratio is a simple index to evaluate atrial contribution to ventricular filling. The AFF represents the proportion of transmitral blood flow during the atrial contraction phase to total diastolic transmitral blood flow provided the mitral valve area is constant during diastole [8].
Cardiac Catheterization Study
Eight patients in the maze group (excepting patients 3 and 6) and all 7 patients in the control group underwent postoperative cardiac catheterization. In the maze group, cardiac catheterization was performed 1 month to 5 months after the operation and in the control group, 1 month postoperatively.
Biplane left atrial angiograms were obtained at 60 frames per second with 35-mm cine film with injection of 40 mL of contrast medium at a rate of 20 mL/s into the pulmonary artery. Electrocardiographic signals were recorded on the cine film. Left atrial volume was calculated with the biplane area-length method as described by Sauter and associates [12]. Left atrial maximal volume (LAmax) was measured at the point of end-systole, left atrial minimal volume (LAmin) at the point of the R wave on the electrocardiogram, and left atrial volume before atrial active emptying (LApreP) at the onset of the P wave. Left ventricular end-diastolic volume and left ventricular end-systolic volume were measured using the single-plane area-length method. All angiographic measurements were made using the Cardio 500 angiographic analysis system (Contron Instruments Inc, Everett, MA).
From the left atrial and left ventricular volume measurements, the following values were obtained; left atrial total emptying volume (LAmax - LAmin); left atrial passive emptying volume (LAmax - LApreP); left atrial active emptying volume (LApreP - LAmin); left atrial conduit volume (left ventricular stroke volume - left atrial total emptying volume); and left atrial emptying fraction (left atrial total emptying volume/LAmax).
Statistical Analysis
Statistical analysis was performed using unpaired t test and regression analysis. Data are presented as the mean +/- one standard deviation. A p value of less than 0.05 was considered significant.
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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. The left ventricular ejection fraction, heart rate, and other values derived from routine M-mode measurements did not differ significantly between the two groups. No mitral regurgitation or paravalvular leak was detected in any patient. As for the transmitral flow measurements, the peak E wave was significantly higher in the maze group, whereas the difference in peak A wave was not significant. The A/E ratio and the AFF were significantly lower in the maze group. An A wave could not be recorded for 1 patient (patient 4) in the maze group, although clear Doppler recordings were obtained and the patient had sinus rhythm on the electrocardiogram.
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). In the control group, both had a tendency to correlate positively with age as previously reported by several groups [9--11] and were within the normal limits shown by them. In the maze group in contrast, the A/E ratio and AFF correlated inversely with age (r = -0.72, p = 0.02 and r = -0.76, p = 0.01, respectively).
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. On left atrial angiograms, active left atrial contraction synchronized with the P wave on the electrocardiogram was detectable in all 8 patients studied in the maze group, although it was sluggish in some. Average LAmax index in the maze group was markedly larger than that in the control group. Left atrial passive emptying volume index was significantly larger in the maze group. On the other hand, left atrial active emptying volume index was significantly larger in the control group. Accordingly, early diastolic left atrial passive volume change was dominant in the maze group, and late diastolic active volume change was dominant in the control group. Average conduit volume index was significantly larger in the maze group.
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) but had no significant correlation with left ventricular ejection fraction or left ventricular stroke volume index. The LAmax index had a tendency to correlate positively with age in the maze group but did not reach significance.
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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On Doppler echocardiography, evidence of left atrial active contraction was detected in 9 of 10 patients in the maze group. However, the average A/E ratio and AFF were significantly smaller than those in the control group. It is more noteworthy that the A/E ratio and the AFF correlated inversely with age in the maze group (see Figs 1, 2
). In a healthy population, the A/E ratio increases with age and exceeds 1.0 around the age of 60 years [11]. We used the A/E ratio and the AFF as variables of left atrial function, but it should be noted that these indices are also largely affected by ventricular stiffness and are sometimes used as indices of left ventricular compliance.
Usually, the A/E ratio and the AFF increase as the left ventricular compliance decreases because of left ventricular hypertrophy or aging. In addition, the A/E ratio and the AFF are affected by atrial compliance, preload, restriction caused by the pericardium, and many more factors other than atrial contractility [10, 13]. Therefore, these two variables may not directly represent the potential contractility of the left atrium itself. However, the transmitral velocity curve can be regarded as representative of the particular hemodynamic state resulting from these various contributing factors. Therefore, our data may not affirm that potential left atrial contractility is impaired in the elderly, but they do show that atrial contraction does not play a major role in ventricular filling at rest.
It must be noted that relatively young patients had nearly normal A/E ratios and AFF values. Therefore, young patients would appear to be better candidates for the maze operation with a mitral valve operation.
High early filling speed in transmitral flow measurements in the maze group appeared to be due to a relatively small mitral valve area of the prosthetic valve compared with that of the native valve.
The left atrium acts as a reservoir, a booster pump for ventricular filling, and a conduit between the pulmonary veins and the left ventricle. During ventricular systole, the left atrium passively dilates and stores energy by receiving blood from the right side of the heart and the lung. In early diastole, the left atrium discharges energy and stored blood into the left ventricle. Atrial active contraction then occurs in late diastole [12, 14]. The angiographic studies demonstrated that a larger part of the diastolic volume change in the left atrium occurred in early diastole as a passive event in the maze group, a finding contrary to the results in the control group. The reservoir and conduit functions of the left atrium played a major role in the maze group.
Kagawa and associates [15] reported in their angiographic study of a healthy population that conduit volume correlated highly with left ventricular stroke volume. Therefore, the larger conduit volume index in the maze group may be due to a larger left ventricular stroke volume.
Murray and associates [16] measured left atrial and left ventricular volumes angiographically in 22 healthy individuals and found that the average LAmax index and LAmin index are 35 +/- 8.7 mL/m2 and 18 +/- 7.4 mL/m2, respectively. In our control group, average left atrial volume was almost equal to the normal value, but in the maze group, left atrial dilatation was apparent in every phase.
Further, the left atrial emptying fraction was significantly lower in the maze group than in the control group. Stagnation of blood in the left atrium is, accordingly, not completely resolved by the operation. Therefore, the risk of thrombus formation in the left atrium did not seem to be remarkably reduced in patients with a giant left atrium. A recent study by the Stroke Prevention in Atrial Fibrillation Investigators [17] revealed that left atrial size is one of the strong independent predictors of thromboembolism. Some additional procedures, such as resection of the redundant atrial wall along the incision line [4, 5], may be beneficial to reduce the size of the left atrium and decrease blood stagnation and thus further decrease the risk of thromboembolism. Postoperative anticoagulation should perhaps be considered after a maze operation done concomitantly with mitral valvuloplasty, even if the patient is in sinus rhythm on the electrocardiogram, unless left atrial contractions are apparent and left atrial size is nearly normal on echocardiographic or other studies.
We selected patients who had undergone coronary artery bypass grafting as controls. As already mentioned, left atrial function and left ventricular function are closely interrelated. Therefore, controls who have left ventricular performance equal to that of the maze group and normal atrial function are ideal for making a fair comparison of atrial function using echocardiographic or angiographic methods as we did. In other words, a healthy population is not ideal as a control group because their left ventricular function is usually far better than that of patients who have had a mitral valve operation. On the other hand, patients who have undergone a mitral valve procedure without the maze operation and are in sinus rhythm do not necessarily have normal left atrial function because the left atrium may be more or less affected by the preoperative valvular lesion.
Echocardiographic variables concerning left ventricular function and pulmonary capillary wedge pressure and cardiac output on cardiac catheterization study were not significantly different between the two groups in this study, although left ventricular volume was larger in the maze group. The gross left ventricular function could be considered almost equal in both groups, although the etiologies were different. The control group in this study may not be ideal, but it makes sense as a reference with a normal left atrium.
Older age and left atrial dilatation seemed to have negative effects on atrial contraction in the maze group (see Figs 1 through 3). However, most of the elderly patients in our series had a rheumatic valvular lesion, and rheumatic degenerative changes in the atrial wall may have impaired atrial contractility. In addition, we could not detect the precise time of onset of the chronic AF in most of the patients. It was not clear from our results whether the duration of chronic AF affected postoperative atrial function. A larger number of patients is needed to detect other determinants of postoperative atrial function.
Finally, we emphasize that we are not negative about the benefit of the maze operation as a combined procedure with a mitral valve operation provided the maze operation can be performed with minimal additional morbidity. It is noteworthy that in relatively young patients, left atrial function estimated with Doppler echocardiography was nearly normal despite severe dilatation of the left atrium. Even in the elderly, resolution of both an inappropriate response in heart rate to exercise and irregular ventricular filling because of AF may be of great benefit.
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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References |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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