(Circulation. 1995;91:2392-2399.)
© 1995 American Heart Association, Inc.
Articles |
Delayed Improvement in Exercise Capacity With Restoration of Sinoatrial Node Response in Patients After Combined Treatment With Surgical Repair for Organic Heart Disease and the Maze Procedure for Atrial Fibrillation
From the Division of Cardiology, Department of Medicine (J.T., T.Y., H.T., Y.O.), Department of Cardiovascular Surgery (Y. Kosakai, Y. Kawashima), and Laboratory of Clinical Physiology (E.O.), National Cardiovascular Center, Suita, Osaka, Japan.
Correspondence to Jun Tamai, MD, Division of Cardiology, Department of Medicine, National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita, Osaka 565, Japan.
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Abstract |
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 Top Abstract IntroductionMethods Results Discussion References |
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Background Although the Maze procedure successfully restores sinus rhythm in patients with heart disease and atrial fibrillation, it is still uncertain whether an addition of the Maze procedure in cardiac surgery is beneficial for exercise performance of the patients after surgery.
Methods and Results The Maze procedure was performed in 25
patients (age, 37 to 70 years) during valve surgery (18 patients) or
closure of atrial septal defect (7 patients). A cardiopulmonary
exercise test using ramp incremental protocol (15 W/min) was performed
before and 1 month, 6 months, and 1 year after surgery. Sinus
conversion was obtained in 23 of 25 patients 1 month after surgery.
However, sinoatrial (SA) node response to exercise was attenuated by
surgery: Mean heart rate (HR) was 83±13/min at rest, 94±13/min
at 60
W, and 107±17/min at peak exercise. Peak oxygen uptake
(P
2) was unchanged at this
period (before, 17.6±4.5
mL · min-1 · kg-1; 1 month
after,
17.5±4.2
mL · min-1 · kg-1).
Thereafter, SA node response was restored 6 months after surgery: Mean
HR was 84±13/min at rest, 104±16/min at 60 W, and
130±20/min at peak
exercise (P<.01 versus 1 month).
P2 was also improved at
this
period (20.7±4.0
mL · min-1 · kg-1,
P<.01). The increase in
P2 from 1 month to 6 months
after surgery was correlated with the increase in peak HR
(y=0.73x±3.6, r=.79). There
were no further changes in heart rate response or
P2 from 6 months to 1 year
after surgery.
Conclusions Atrial fibrillation was successfully treated by combined treatment with surgical repair for organic heart disease and the Maze procedure. However, SA node response to exercise was attenuated early after surgery. Thus, exercise capacity was improved at the late phase after surgery, which was related to the extent of restoration in SA node response.
Key Words: exercise • surgery • fibrillation • heart diseases
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Introduction |
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TopAbstractIntroductionMethods Results Discussion References |
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The Maze procedure, a novel surgical treatment for atrial fibrillation, was initially described by Cox and associates.1 2 3 4 Although this method requires relatively invasive surgical technique, that is, multiple incisions in the atrial wall, the initial results of their institution3 and others5 have shown that this method is highly successful in restoration of sinus rhythm in patients with lone atrial fibrillation. Recently, the Maze procedure was applied to atrial fibrillation associated with heart diseases, and preliminary reports indicate that combined treatment with surgical repair for organic heart disease and the Maze procedure for atrial fibrillation was also successful.6 7 We also reported that sinus conversion was obtained in 52 of 62 patients with valvular heart disease and atrial fibrillation by this combined surgery.8 Although the effect of the Maze procedure on restoring sinus rhythm is well documented, other consequences of the Maze procedure due to multiple incisions in the atrial wall have not been well examined yet. Preliminary examination suggests poor response of the sinoatrial node to exercise after surgery,9 which may have detrimental effects on the exercise performance of the patients. An addition of the Maze procedure in cardiac surgery might be less valuable if the exercise capacity was not improved even though sinus conversion was obtained: Improvement of exercise capacity is one of the major clinical goals of the surgery for patients with heart diseases.
The purposes of the present study were to determine whether the combined treatment of surgical repair for organic heart disease and the Maze procedure for atrial fibrillation improves the exercise performance of the patients with heart disease and atrial fibrillation and to examine whether an addition of the Maze procedure is of value in surgical treatment of the patients with heart disease and atrial fibrillation.
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Methods |
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TopAbstractIntroductionMethods Results Discussion References |
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Subjects
Twenty-five patients who received cardiac surgery with the Maze procedure were enrolled in this study. Informed consent was obtained from each patient. The clinical characteristics of each patient are listed in Table 1
. Patients comprised 15 men and 10
women, and their ages were 37 to 70 years (mean, 57±8 years). Atrial
fibrillation was permanent in 23 patients and paroxysmal in 2. Duration
of atrial fibrillation was 0.7 to 20 years (mean, 7±7 years). In 2
patients with paroxysmal atrial fibrillation, 1 (No. 12) suffered from
rapid ventricular response during the attack once a week despite the
medical treatments and another (No. 16) repeated hospitalization for
the treatment of exaggerated congestive heart failure induced by
paroxysmal atrial fibrillation. Organic heart diseases were valvular
heart disease in 18 patients and atrial septal defect in 7. In patients
with atrial septal defect, 3 had mitral valve regurgitation and 4 had
tricuspid valve regurgitation. These patients also received valve
repair. There were 6 reoperated cases in patients with mitral valve
disease. The initial procedures were mitral valve replacement in 3,
mitral valve plasty in 2, and open mitral commissurotomy in 1. The
interval between the two operations was 2 to 15 years.
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Maze Procedure
In April 1992, the surgical department of our
institution
started to apply the Maze procedure in cardiac surgery of the patients
with organic heart disease and atrial fibrillation. Initially, the
application of the combined surgery was limited in selected patients.
Since September 1992, the combined surgery was performed when possible
in the cardiac surgery of consecutive patients with valvular or
congenital heart disease and atrial fibrillation. However, patients who
required emergency surgery and those with severe heart failure were
omitted because of the need to shorten cardiopulmonary bypass
time.8
The operative procedure was fundamentally the same as that initially described by Cox and associates.4 However, several modifications were made in the patients used in the present study.10 In brief, a longitudinal incision of right atrial free wall was performed from the right atrial appendage (instead of the superior vena cava) down to the inferior vena cava because Cox's original incision transverses the sinus node arteries and deteriorates the postoperative sinus node function.11 In addition, other incisions that transverse sinus node arteries were substituted by cryosurgical procedure to avoid an interruption of sinus node arteries. Patients 5 through 25 received this modification. Second, in patients who required surgical treatments for the mitral valve, division of the superior vena cava was performed to improve the exposure of the mitral valve to shorten the operative time. This modification was also performed by Dr Cox in his first modification of the Maze procedure.12
Cardiopulmonary Exercise Testing
Exercise capacity of each
patient was examined by a
symptom-limited exercise test. The exercise test was performed on an
upright bicycle ergometer (Combi 232C). Exercise workload was increased
by a ramp incremental protocol of 15 W/min after 1-minute warm-up at 0
W. Exercise was continued until the patient complained of symptomatic
limits on dyspnea or leg fatigue, that is, 19 to 20 on the Borg
scale.13 During the exercise test, heart rate was
continuously monitored, and blood pressure was measured every minute.
Expired gas of the patient was measured on a breath-by-breath basis
during the test using a respiromonitor AE280 (Minato Medical Science)
connected to a personal computer with analyzing software.
Respiratory gas was analyzed as a value of averaged data every 15 seconds. Peak oxygen uptake was defined as a value of averaged data in the final 15 seconds of the exercise.
All patients performed the symptom-limited exercise test 1 week before the surgery and 1 month and 6 months after the surgery. The initial 10 patients performed an additional exercise test 1 year after the surgery.
Statistical Analysis
Data are presented as mean±SD.
Variables obtained at
rest, at an equivalent workload, and at peak exercise were compared
using repeated-measures ANOVA and Scheffe's F test. Linear regression
analysis was used to evaluate the relation between the two
variables. A P value of less than .05 was considered
significant.
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Results |
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TopAbstractIntroductionMethods Results Discussion References |
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Cardiopulmonary Bypass Time and Cardiac Arrest Time of Combined Surgery
Cardiopulmonary bypass time of the patients ranged from 119 to 291 minutes (mean, 210±47 minutes). Cardiac arrest time during surgery ranged from 75 to 217 minutes (mean, 137±32 minutes).
Effects of Combined Surgery on Left Atrial and Ventricular Chamber
Dimension and Function
Echo-Doppler examination indicated significant
decrease in left
atrial dimension after surgery (P<.01). Atrial wave in
transmitral flow profile was observed in 14 of 25 patients (Table
2). Although mean values of left ventricular dimension
and fractional shortening did not change after the surgery, effects of
surgery on these variables were equivocal because of the differences in
preoperative conditions of each patient.
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Postoperative Cardiac Rhythm and Drug Administration
Sinus
rhythm was obtained in 23 of 25 patients (92%) 1 month
after the surgery. In the remaining 2 patients, 1 patient showed
junctional rhythm and later changed to sinus rhythm and 1 patient
continued atrial fibrillation for 6 months. Thus, 6 months after the
surgery, atrial fibrillation associated with heart diseases was
converted to sinus rhythm in 24 of 25 patients (96%) examined.
Digitalis was administered in 23 patients before the surgery and was continued in patients who still had clinical symptoms of congestive heart failure after surgery. Therefore, digitalis was continued in 11 of 23 patients with sinus rhythm 1 month after the surgery and in 10 of 24 patients with sinus rhythm 6 months after the surgery. A class Ia antiarrhythmic drug was also administered in 17 patients 1 month after the surgery and in 11 patients 6 months after the surgery because they had frequent atrial arrhythmia after surgery.
Cardiopulmonary Response to Exercise
Fig 1
shows the representative ECGs at rest
and at peak exercise. Fig 2 shows the
representative trend graphs of heart rate and oxygen uptake
during the exercise tests. Although sinus conversion was obtained 1
month after the surgery, heart rate response was markedly attenuated
(minimal increase during exercise and delayed decrease during the
recovery period). However, 6 months after the surgery, heart rate
response was almost normalized; there was a small increase in heart
rate at the onset of exercise, high heart rate at peak exercise, and a
rapid decrease in heart rate immediately after cessation of
exercise. On the other hand, an increase in oxygen uptake during
exercise was almost equivalent in the repeated exercise tests, and peak
oxygen uptake apparently increased 6 months after the surgery.
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—), and 6 months
after (—
—) combined
surgery with the Maze procedure. Arrows indicate peak exercise.
The mean
values of heart rate and oxygen uptake in 23 patients with
sinus rhythm 1 month after the surgery are summarized in Fig 3.
Heart rate at the resting condition did not change.
Peak heart rate was 172±23.2/min before surgery due to a rapid
ventricular response of atrial fibrillation. Although sinus rhythm was
obtained 1 month after the surgery, peak heart rate was only
107±16.7/min (P<.01 versus before surgery). However, it
increased to 130±20.2/min 6 months after the surgery
(P<.01 versus before and 1 month after surgery).
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Duration
of preoperative atrial fibrillation was correlated with
neither heart rate response 1 month after surgery (r=.12)
nor increase in peak heart rate from 1 to 6 months after surgery
(r=.14). There were 4 patients with atrial septal defect who
did not receive the division of the superior vena cava. The peak heart
rate of these patients was 110±16.9/min 1 month after the surgery and
129±11.4/min 6 months after the surgery, which was not different from
the patients with the division of superior vena cava (1 month after
surgery, 106±17.0/min; 6 months after surgery, 130±21.8/min).
Digitalis was administered in 11 patients after the surgery; however,
no statistical differences were observed in resting heart rate or its
response to exercise between the patients with and without digitalis
administration (Table 3).
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Peak oxygen uptake did not
increase 1 month after surgery (950±300
mL/min, 17.6±4.5
mL · min-1 · kg-1)
as compared with that before surgery (940±310 mL/min, 17.5±4.2
mL · min-1 · kg-1). However,
concomitant with increases in heart rate during the exercise, peak
oxygen uptake significantly improved 6 months after surgery (1160±350
mL/min, 20.7±4.0
mL · min-1 · kg-1,
P<.01, versus 1 month after surgery). Moreover, the extent
of increases in peak oxygen uptake and peak heart rate from 1 month to
6 months after surgery were closely correlated (r=.79,
P<.01, Fig 4). However, peak oxygen uptake
was not different between patients with and without atrial wave in
transmitral flow.
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Peak oxygen pulse (peak oxygen uptake divided by peak
heart rate)
significantly increased 1 month after surgery as compared with that
before surgery (5.5±1.5 to 8.5±2.4 mL, P<.01), but
it did
not show further changes 6 months after surgery
(8.9<27.2.2 mL). On the other hand, a slope of the relation between oxygen
uptake and workload (|gDoxyg>±2.2
mL). On the other hand, a slope of the relation between oxygen uptake
and workload (
oxygen uptake/work ratio) increased from 1 to 6
months after surgery (Fig 5).
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Systolic blood pressure
became higher 6 months after surgery compared
with conditions before and 1 month after surgery, whereas ventilatory
response did not show any changes in the repeated exercise tests (Fig
6).
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), 1
month after
(
), and 6
months after
(
)
combined surgery with the Maze procedure. **P<.01 vs
before
surgery; ##P<.01 vs 1 month after surgery. Ex indicates
exercise.
Symptom-limited exercise testing was again performed
1 year after the
surgery in 10 patients. However, there were no further changes in rest
heart rate, peak heart rate, or peak oxygen uptake from 6 months to 1
year after surgery (Table 4).
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There was one unsuccessful
case who showed atrial fibrillation
even 6 months after surgery. Although the same dose of digitalis was
administered in this patient, both an increase in ventricular rate
during mild to moderate extent of exercise and its decrease during the
recovery period remained attenuated after surgery (Fig 7).
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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The present study demonstrates that (1) the Maze procedure was highly successful even in patients with atrial fibrillation associated with heart disease, (2) sinoatrial node response to exercise was not restored in the early phase after surgery but was recovered in the late phase after surgery, and (3) the extent of recovery in sinoatrial node response correlated with the extent of the improvement in exercise capacity of the patients.
Application of the Maze Procedure to the Surgery of Patients
With Heart Disease and Atrial Fibrillation
Initial candidates of the
Maze procedure were patients with lone
atrial fibrillation.3 Although atrial fibrillation is the
most common arrhythmia in the subjects without heart
disease,14 it is also a common complication of patients
with heart disease. Previous reports indicate that the Maze procedure
restored sinus rhythm even in patients with heart
disease.6 7 8 9 Thus, the
Maze procedure will be of much more
value if it can be applied to cardiac surgery for patients with heart
disease.
The results of the present study and a previous report8 showed that addition of the Maze procedure required a longer bypass run and cardiac arrest, which might cause postoperative morbidity. However, we also examined the risk and benefit of combined Maze procedure in the surgery of patients with valvular heart diseases and concluded that the restoration of sinus rhythm by an addition of the Maze procedure was worthwhile despite the longer operative time, larger blood loss, and longer postoperative respiratory care.15
The present study showed an increase in peak oxygen uptake of the patients after combined surgery with the Maze procedure. Because an improvement of exercise capacity is one of the major clinical purposes of the surgery for patients with heart diseases, we believe that the results of the present study enhance the clinical value of the Maze procedure in cardiac surgery.
Attenuated Sinoatrial Node Response to Exercise After the Maze
Procedure
The attenuated heart rate response 1 month after surgery was
characterized as follows: no increase in heart rate at the onset of
exercise, low heart rate at peak exercise, and no decrease in heart
rate immediately after cessation of exercise (Fig 2
). This
heart rate
response can be mimicked in the experimentally denervated
heart16 and transplanted heart.17 Thus, the
attenuated heart rate response to exercise early after the Maze
procedure is seemingly caused by the denervation of the sinoatrial node
due to multiple incisions in atrial wall.
The present study also demonstrates the recovery of heart rate response 6 months after surgery. If the attenuated heart rate response early after the Maze procedure is caused by denervation of the sinoatrial node, its recovery late after surgery is also consistent with the time course of reinnervation of the sinoatrial note; reinnervation of the parasympathetic nerve was observed as early as 26 days and that in the sympathetic nerve was as early as 74 days after experimentally denervated heart.18 Moreover, we examined the sinoatrial node response of the patients with mitral stenosis and atrial fibrillation who received balloon mitral commissurotomy and thereafter converted to sinus rhythm by the electrical cardioversion.19 Although this combined therapy was almost the same as the combined surgery except for the surgical procedures, heart rate reached 146±14/min at peak exercise 5 days after sinus conversion, and further augmentation of peak heart rate was not observed in the late phase after electrical cardioversion. Thus, these lines of evidence lead to the hypothesis that the attenuated sinoatrial node response to exercise early after combined surgery may be caused by the denervation of the sinoatrial node due to the Maze procedure, and its recovery late after surgery represents the time course of reinnervation of the sinoatrial node.
Heart Rate Response and Exercise Capacity
An increase in
heart rate plays an important role in raising
cardiac output during exercise, which is demonstrated by the direct
linear relation between heart rate and cardiac output during
exercise.20 Thus, the attenuated sinoatrial node response
early after the Maze procedure undoubtedly deteriorates the exercise
capacity of the patient. However, the peak oxygen uptake was preserved
(Fig 3) as compared with that before surgery by increasing peak
oxygen
pulse (Fig 5). Oxygen pulse is the product of stroke volume and
arteriovenous oxygen difference. The previous report indicated that the
augmentation of these two factors was observed during exercise in
patients with poor heart rate response due to heart
transplantation.21 Moreover, an increase in stroke volume
could be accomplished by the surgical repair of heart disease in
patients we examined. Thus, both factors play major roles in preserving
exercise capacity of the patient despite the attenuated heart rate
response early after combined surgery.
An improvement of sinoatrial
node response in the late phase after the
surgery increased both the peak oxygen uptake (Fig 3) and
oxygen
uptake/work ratio (Fig 5), which indicates the
amelioration of
impaired oxygen uptake.22 However, the extent of the
improvement in exercise capacity was not uniform and depended on the
recovery of heart rate response (Fig 4). We could not find any
relation
between the extent of recovery in heart rate response and preoperative
characteristics or surgical procedures of each patient. Whatever the
cause of this difference, the present results indicate that the
more the heart rate response recovers, the more the exercise capacity
improves. Because the changes in heart rate response after surgery
appear to depend on the extent and rate of denervation and
reinnervation of the sinoatrial node, maneuvers to avoid denervation
and/or to enhance reinnervation may have advantageous effects on the
exercise capacity of the patient after surgery.
Limitations of the Study
First, administration of drugs was
not discontinued when patients
performed the exercise test because it was uncertain whether atrial
fibrillation might occur even if the drugs were discontinued. However,
there were no statistical differences in heart rate response between
patients with and without digitalis (Table 3). Second, the
modifications of the operative procedure were performed in the series
of patients we examined. Application of cryosurgical procedure may
influence the results of the present study. Moreover, comparison of
the data between the patients with and those without division of the
superior vena cava is not conclusive because of the small number of
patients in the latter group.
Conclusions
The combined treatment of surgical repair for
heart disease and
the Maze procedure for atrial fibrillation improved the exercise
capacity of the patients. This combined surgery was of value for the
patients with heart disease and atrial fibrillation; however, the
extent of improvement in exercise capacity after the surgery largely
depended on late recovery of the sinus node response to exercise.
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Acknowledgments |
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The authors thank Dr Masafumi Kitakaze for valuable comments and revision of the manuscript.
Received September 13, 1994; accepted November 26, 1994.
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References |
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