Circulation. 1995;92:216-222
(Circulation. 1995;92:216-222.)
© 1995 American Heart Association, Inc.
Peak Oxygen Consumption and Resting Left Ventricular Ejection Fraction Changes After Cardiomyoplasty at 6-Month Follow-up
Edimar Alcides Bocchi, MD;
Guilherme Veiga Guimarães, PhEd;
Luiz Felipe P. Moreira, MD;
Fernando Bacal, MD;
Alvaro Vilela de Moraes, MD;
Antonio Carlos Pereira Barreto, MD;
Mauricio Wajngarten, MD;
Giovanni Bellotti, MD;
Noedir Stolf, MD;
Adib Jatene, MD;
Fulvio Pileggi, MD
From the Heart Institute, São Paulo (Brazil) University Medical
School.
Correspondence to Edimar Alcides Bocchi, MD, Rua Oscar Freire, 2077, Apto
161, Cep 05409-011, São Paulo, Brasil. E-mail:
dcl_edimar@pinatubo.incor.usp.br.
 |
Abstract
|
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Background The effects of cardiomyoplasty on
cardiopulmonary
exercise test characteristics are not fully
known.
Methods and Results We determined in 19 patients who
underwent cardiomyoplasty for treatment of refractory heart failure
(New York Heart Association [NYHA] functional class III) before
(pre)
and at 6-month follow-up (post) maximum oxygen consumption (peak
O2), NYHA functional class,
and resting
left ventricular ejection fraction (LVEF) (MUGA). We
analyzed the results according to pre peak
O2 < or >14 mL/kg per
minute and the correlation between the changes in absolute values of
LVEF and peak
O2.
Pre and postpeak
O2 values were
15.9±4.4 and 18.6±6.4
mL/kg per minute, respectively (P=.059). In the subgroup
with prepeak
O2
<14 mL/kg per minute,
the peak
O2 increased from
11.1±1.9 to
16.4±6.2 mL/kg per minute (P=.02). The subgroup with
peak
O2 >14 mL/kg per minute
showed pre
and postpeak
O2 of
19.2±2.6 and of
20.1±7 mL/kg per minute, respectively (P=.06). The
pretotal exercise time of the entire group increased from
688.4±222.1 to 833.7±241.6 seconds (P<.04). For the
subgroup with preoperative peak
O2 <14
mL/kg per minute, exercise time improved from 585±76.9 to
825±186.3
seconds (P<.01). In the subgroup with preoperative
O2 >14 mL/kg per minute,
the preexercise and postexercise time was 763.6±264.4 and
840±282
seconds, respectively (P=.4). Pre- LVEF increased from
20.6±3.3% to 24.2±7.8% at 6 months of follow-up
(P=.02). At 6 months of follow-up, 9 patients were in
NYHA functional class I and 10 were in class II. There was no
correlation between LVEF values and absolute values of peak
O2 before
(r=.123,
P=.6) and after (r=.27, P=.2)
cardiomyoplasty. A weak correlation was observed between the changes in
absolute values of peak
O2
and LVEF from
the preoperative to the postoperative period (r=.48,
P=.048).
Conclusions Cardiomyoplasty is a useful method for
improving NYHA functional class and LVEF in patients with heart
failure. Peak
O2 <14
mL/kg per minute
before cardiomyoplasty may be a selection criterion with which
to determine improved exercise capacity after surgery. The effects of
cardiomyoplasty on LVEF appear to be partially associated with maximum
exercise capacity changes.
Key Words: cardiomyoplasty heart failure exercise
 |
Introduction
|
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Dynamic cardiomyoplasty is a surgical
procedure directed toward
treatment of heart failure.
1 In
this procedure, a latissimus
dorsi muscle flap is wrapped around the
ventricles and stimulated
in synchrony with cardiac systolic
activity.
2 3 In selected
patients, studies have shown
that
the procedure improves New
York Heart Association (NYHA) functional
class,
4 5 6 7 left
ventricular
function,
8 regional left ventricular wall
motion with changes in geometry,
9 and
hemodynamic parameters at rest and during
exercise.
10 In addition, there has been a report of an
increase in left
ventricular maximal elastance and
reduction of systolic wall
stress,
end-diastolic circumferential stress, and chamber and
muscle
stiffness associated with changes in left
ventricular diastolic
filling.
11
Also, improvement in maximum oxygen consumption (peak
O2) during exercise has
been
demonstrated.6 10 12 However, these
previous studies did
not describe other treadmill exercise characteristics, and they were
limited by a small number of patients7 or associated
procedures to cardiomyoplasty.12 In addition, these
studies did not provide selection criteria for improvement in
peak
O2 after
cardiomyoplasty.
Accordingly, the purpose of the present study was to investigate
the effects of dynamic cardiomyoplasty on cardiopulmonary
treadmill exercise test characteristics and resting left
ventricular ejection fraction (LVEF) at 6-month
follow-up. Also, we studied the correlation between the absolute
values of preoperative peak
O2 and its
improvement after cardiomyoplasty.
 |
Methods
|
|---|
Study Population
In the study period from May 1988 to March
1993, 32 patients
underwent
cardiomyoplasty at Heart Institute, University of São
Paulo
(Brazil) Medical School. None of the patients died in the
immediate
postoperative period, but one patient had to have heart
transplantation.
Three patients died before 6-month follow-up. Nine
patients
were excluded owing to the following reasons: sustained
ventricular
tachycardiac episode during
exercise (1), atrial fibrillation
with high ventricular
rate during exercise (1), technical limitation
in interpreting the test
(1), nonadherence to protocol (1 [from
Venezuela]), limitations in
determining peak
O2 because
of
osteomuscular
disease, or any reason other than dyspnea or fatigue,
such as
obesity (1), anxiety (1), recent respiratory tract infection
(1),
and not reaching the anaerobic threshold (2).
Accordingly, the
study group consisted of 19 patients. The selection of
patients
for cardiomyoplasty was performed with previously described
criteria.
13 The diagnosis was idiopathic dilated
cardiomyopathy in 16 patients,
Chagas' heart
disease in 1, and ischemic cardiomyopathy
in 2.
Fifteen patients were men, and mean age was 47±6 years
(range,
33 to 55 years). Before cardiomyoplasty, all patients
were in New York
Heart Association (NYHA) functional class III
despite maximal medical
therapy with diuretics, digitalis, vasodilators
(ECA
inhibitors), and potassium reposition beyond the standard
treatment
of heart failure. The doses of diuretics were reduced
or remained
the same, and the doses of vasodilators did not change at
6-month
follow-up. Patients were asked to provide written special
informed
consent in accordance with the standards of the Scientific and
Ethic
Committee of the Heart Institute, University of São Paulo
Medical
School. Table 1

shows additional characteristics
of patients
studied.
Surgical Procedure and Muscle Stimulation Protocol
Cardiomyoplasty was performed in accordance with the
reinforcement technique described by Chachques et al.14
All operations were performed without cardiopulmonary
bypass. Two intramuscular pacing electrodes (Medtronic SP 5528 BV) were
implanted in the muscle flap. An intramyocardial sensing lead
(Medtronic SP 5548 BV) was implanted in either the left or the right
ventricle. The cardiomyostimulator Medtronic SP 1005 BV was used for
muscle stimulation.
Electrical stimulation of the skeletal muscle graft
was initiated 2
weeks after the operation. The progressive muscle-conditioning
protocol proposed by Chachques et al3 was followed. After
2 months of follow-up, the stimulation frequency of 30 Hz was
achieved, and the muscle flap was paced at 1:1 with a heart rate <100
beats per minute (bpm) and 2:1 with a heart rate >100 bpm.
Supramaximal pulse amplitude values (4.5 to 6 V) were used for muscle
stimulation. The delay between the sensed ventricular event
and the muscle burst was adjusted to obtain exact synchronization
between muscle flap contraction and ventricular
systole.10
Study Design
Before and at 6-month follow-up after
cardiomyoplasty we
determined the following parameters: NYHA functional class,
resting LVEF (in percent) by radionuclide scintigraphy,
peak
O2 normalized for body
weight
during cardiopulmonary treadmill exercise, total exercise
time, heart rate, and maximum pulmonary ventilation. In
addition to standard analysis of patient data, we compared the
results of two subgroups according to peak
O2 before the
cardiomyoplasty: >14 and
<14 mL/kg per minute. The limit was considered to be 14 mL/kg per
minute on the basis of the importance of this value in the indication
for heart transplantation, and this limit is related to an unacceptable
quality of life.15 The subgroups had similar baseline
characteristics before cardiomyoplasty except for peak
O2 (Table
1
).
Furthermore, the correlation between resting LVEF changes and peak
O2 was studied to clarify
the mechanisms
of cardiomyoplasty effects. The changes in parameters were
calculated according to the differences between the postoperative and
preoperative absolute values.
Cardiopulmonary Exercise Test
On the day before the study,
treadmill exercise was performed to
familiarize the patients with the protocol. On the next day, the
subjects underwent 12-lead resting ECG and a progressive treadmill
exercise test, with continuous monitoring of ECG, cuff blood pressure,
ventilation, and gas exchange during the test, including the recovery
period. Subjects were asked to refrain from cigarette smoking and
consumption of caffeinated beverages on the day of the test. All
patients were studied in an air-conditioned (21°C to 23°C)
exercise facility at least 2 hours after a light meal. The exercises
were performed on a programmable treadmill (Quinton Instrument Co)
according to a modified Naughton protocol.16 After 2
minutes of resting recordings while on the treadmill, all
patients were encouraged to exercise until symptoms (fatigue or
dyspnea) made them unable to continue. All patients reached the
anaerobic threshold. Expired fractions of O2
(by zirconium fuel-cell sensor) and CO2 (infrared
absorption) and the rate of air flow were measured by
metabolic analyzer and by the linearized
pneumotachometer at rest (standing) and throughout the exercise period
and recovery with a breathing apparatus consisting of a
mouthpiece, nose clamp, and low-resistance two-way valve (dead
space, 100 mL; Hans-Rudolph). Ventilatory and gas exchange data were
determined on a breath-by-breath basis with a computerized
system (model CAD/Net 2001, Medical Graphics Corporation). The
following measurements were derived on a breath-by-breath
basis: O2 uptake normalized for body weight
(
O2, mL/kg per minute),
CO2 production
(
CO2, mL/min), end-tidal
oxygen partial pressure (PETO2), end-tidal
carbon pressure (PETCO2), ventilatory
equivalent exchange ratio (RER)
(
CO2/
O2),
minute pulmonary ventilation (VE, mL/min), the
ventilatory equivalent for oxygen
(VE/
O2), and the
ventilatory
equivalent for carbon dioxide
(VE/
CO2). Peak
O2 was considered the
highest
O2 achieved in a presumed
maximal effort
exercise test.17 Maximal ventilation was determined by the
average of all breaths within a 30-second period surrounding the
highest recorded
O2. To
determine
anaerobic threshold (AT), the following criteria were
used18 : systematic increase in
VE/
O2 without
increase in
VE/
CO2, systematic
increase in PETO2 without a decrease of
PETCO2, and systematic increase in
RER.
LVEF
Left ventricular radionuclide
scintigraphy was obtained after in vivo labeling of red
blood cells with 99mTc. Gatedblood pool imaging was
acquired in the left anterior oblique view with an Anger Camera 9, Ohio
Nuclear) equipped with an S-500 computer (Sopha Medical Systems, Inc).
Left ventricular volumes and LVEF were calculated by
standard formulas.
Statistical Analysis
Statistical analysis was performed with
Student's
t test for paired or nonpaired testing, as appropriate. A
value of P<.05 was considered statistically significant.
Data are presented as mean±SD. The relations between
variables were examined with linear regression
analysis.
 |
Results
|
|---|
Cardiopulmonary Exercise Test
The mean value of peak
O2 before
the cardiomyoplasty was 15.9±4.4
mL/kg per minute and at 6 months
after the operation was 18.6±6.4
mL/kg per minute
(
P=.059)
(Fig 1

). The subgroup (11 patients)
with
preoperative peak
O2 >14
mL/kg per
minute showed peak
O2 of
19.2±2.6 mL/kg
per minute before the operation
and 20.1±7 mL/kg per minute at 6-month
follow-up (
P=.06)
(Fig 2

).
However, in contrast, the subgroup of patients (8 patients)
with
preoperative peak
O2 <14
mL/kg per
minute presented
a statistically significant improvement in
peak
O2. In this
subgroup,
the peak
O2 increased from
11.1±1.9 to 16.4±6.2
mL/kg
per minute (
P=.02) (Fig 3

). Fig
4

shows a plot
between preoperative
peak
O2 values and
peak
O2 improvement. The
values of
V
E/
O2 of the
entire group
before the operation and at 6-month follow-up
were 54±29 and
54±16 (
P=NS), respectively; 65±42
and
64±19
(
P=NS) in the subgroup with peak
O2 <14
mL/kg per minute
before the
surgery; and 46±9 and 47±10
(
P=NS) in the
subgroup with
preoperative peak
O2 >14
mL/kg
per
minute. The exercise time of the entire group was 688.4±222.1
seconds
before cardiomyoplasty and 833.7±241.6 seconds
after
cardiomyoplasty (
P<.04). In the subgroup with preoperative
peak
O2 <14 mL/kg per
minute, the
exercise time improved from
585±76.9 to 825±186.3 seconds
(
P<.01). In the
subgroup with preoperative
O2 >14 mL/kg per minute,
the
preexercise
and postexercise times were 763.6±264.4 and 840±282
seconds,
respectively (
P=.4). The maximum heart rate during
exercise
for the entire group was 149±26 bpm before cardiomyoplasty
and
153±22 bpm after cardiomyoplasty (
P=NS). In the
subgroup
with preoperative peak
O2 >14 mL/kg per minute,
the preoperative
and postoperative maximum heart rates were 154±30 and
152±21
bpm, respectively (
P=NS). For the subgroup with
preoperative
peak
O2 <14
mL/kg per
minute, the preoperative and postoperative
maximum heart rates were
140±30 and 155±25 bpm
(
P=NS) (Fig
5

).

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Figure 5. Graph showing heart rate during treadmill exercise
test before and after cardiomyoplasty in patients with maximum oxygen
consumption (peak O2)
<14 mL/kg per
minute before the surgery. b · min-1 indicates beats
per minute; pts, patients; N, number; Pre, before surgery; and Post,
after surgery at 6-month follow-up.
|
|
NYHA Functional Class
At 6 months of follow-up 9 patients
were in NYHA functional
class I, and 10 patients were in class II (Table 2
). Therefore,
cardiomyoplasty determined
improvement in NYHA functional class in most surviving patients. Eight
patients with peak
O2
<14 mL/kg per
minute before cardiomyoplasty had improvement of NYHA functional class
from class III to class II (5 patients) or to class I (3 patients). In
the subgroup with peak
O2
>14 mL/kg per
minute before the surgery, NYHA functional class increased from class
III to class I in 6 patients and to class II in 5 patients.
LVEF
Cardiomyoplasty determined improvement in LVEF from
20.6±3.3%
(before surgery) to 24.2±7.8% at 6-month follow-up
(P=.02). Fig 6
shows the individual variation
of LVEF from before surgery to 6-month follow-up. In the subgroup
with preoperative peak
O2
<14 mL/kg per
minute, LVEF improved from 20.4±3.7% to 26.1±11%
(P=.09). In the subgroup with peak
O2 >14 mL/kg per minute
before the
operation, LVEF increased from 21±2.7% to 24±3.2%
(P=.04).

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Figure 6. Plot of left ventricular ejection
fraction by radionuclide scintigraphy at rest before and
after cardiomyoplasty (CMP) in entire study group. Pre CMP indicates
before CMP; Post CMP, after CMP at 6-month follow-up.
|
|
Correlation Between Changes in LVEF, NYHA Functional Class, and
Peak
O2
Table
2
presents an analysis of results on a
patient-by-patient basis. There was no correlation between
resting LVEF values and absolute peak
O2
values before (r=.123, P=.6) and after
(r=.27, P=.2) cardiomyoplasty. Also, there was
no
correlation between NYHA functional class and changes in peak
O2 or LVEF. However, a weak
correlation
was observed for maximum changes in peak
O2 and LVEF between before
cardiomyoplasty and 6-month follow-up (r=.48,
P=.048) (Fig 6
).
 |
Discussion
|
|---|
The results of the present study demonstrate that cardiomyoplasty
improves
LVEF and NYHA functional class in patients with heart failure
by
6-month follow-up. There was a trend that did not achieve
statistical
significance for peak
O2 improvement in the
entire
group. Cardiomyoplasty
improved peak
O2
and exercise time in patients with preoperative
peak
O2 <14 mL/kg per minute.
In addition,
there was a statistically
weak correlation between the changes in left
ventricular ejection
fraction and peak
O2 absolute values from
before cardiomyoplasty
to 6-month follow-up.
Left ventricular function and functional class results are
consistent with results of the US Food and Drug Administration
(FDA) Phase II American Cardiomyoplasty Study and other studies that
showed improvement in LVEF, left ventricular regional wall
motion, and clinical status after
cardiomyoplasty.3 8 9 12 19 20 21 22
Multiple mechanisms have
been proposed to explain the left ventricular
systolic effects of cardiomyoplasty, such as reduction in left
ventricular stress,11 23 improvement in
ventricular wall motion owing to active reinforcement,
passive reinforcement limiting heart dilatation,3 changes
in left ventricular geometry,9 decreased
myocardial
O2, and enhanced
coronary
revascularization.5 24 25 Concerning
NYHA functional class results, despite modest and nonuniform beneficial
effects on left ventricular function and peak
O2, cardiomyoplasty
produced improvement
in NYHA functional class in all patients. This finding is confirmed by
other studies that had difficulty correlating clinical success with
improvement in resting LVEF and resting hemodynamic
data after
cardiomyoplasty.5 22 26 27
The poor correlation
between LVEF at rest and exercise capacity before and after the
cardiomyoplasty are corroborated by studies that demonstrated disparity
between resting measures of left ventricular function and
maximal exercise
capacity.28 29 30 31 Also,
divergence between
improvement in resting LVEF and exercise tolerance with medical
treatment has been reported.32 In the present study,
we found a weak but statistically significant correlation between
changes in LVEF and peak
O2
changes. The
reasons for these findings are unclear. One could speculate that
cardiomyoplasty may have additional effects on other determinants of
NYHA functional class or exercise capacity, such as cardiac
diastolic function or cardiovascular
reserve during exercise and even a placebo effect.
The observed tendency of improvement in peak
O2 during cardiopulmonary
treadmill tests is in contrast to the FDA Phase II American
Cardiomyoplasty Study results.22 However, the improvement
is in concordance with previous reports that showed statistically
significant improvement in maximal exercise capacity after
cardiomyoplasty.12 33 However, the preoperative mean
values of peak
O2 in these
previous
studies were lower than values in the present study, except in the
FDA American Cardiomyoplasty Phase II Study.22 On the
other hand, postoperative data after cardiomyoplasty in our and other
investigations showed peak
O2 values
between 18 and 19 mL/kg per minute.12 27 Also, after
successful heart transplantation, peak
O2 was close to 19 mL/kg
per
minute.34 It appears that methods to treat heart failure
may have limitations in normalizing peak
O2. Thus, the preoperative
value of peak
O2 should be included among
selection
criteria aimed at successful cardiomyoplasty. This assumption may be
supported by our subgroup results that showed a substantial improvement
in patients with preoperative peak
O2
<14 mL/kg per minute. Mechanisms of cardiomyoplasty effects
determining improvement in peak
O2 are
not unknown. Also, pathophysiological
mechanisms underlying the exercise limitation of patients with chronic
heart failure are not clear. It is postulated that in patients with
heart failure35 multiple abnormalities may affect exercise
capacity, such as central (systolic and diastolic
function, pulmonary hemodynamics, and
neurohumoral mechanisms), peripheral (blood flow
abnormalities, vasodilatory capacity, and skeletal muscle
biochemistry), and ventilatory factors (pulmonary pressure,
physiological dead space, ventilation-perfusion
mismatch, respiratory control, and breathing
pattern).36 37 38 It has been postulated
that maximal heart
rate, maximal cardiac output, and their changes from rest to maximal
exercise appear to account for the greatest variances in exercise
capacity.30 39 Resting effects of cardiomyoplasty on
central factors, including systolic and diastolic
left ventricular functions, have been
demonstrated.3 8 Resting hemodynamic
improvement is not a universal finding. However, evaluations were
usually performed at rest and not during exercise. To our knowledge,
only one investigation was performed during exercise, and the
investigators demonstrated improvement in hemodynamics
during treadmill upright exercise after cardiomyoplasty.10
Thus, theoretically one might speculate that a main effect of
cardiomyoplasty during exercise would be to provide higher left
ventricular stroke volume, probably owing to a beneficial
systolic effect and possibly a diastolic effect of
exercise. This can be supported by our results showing no statistically
significant change in maximal exercise heart rate. It is believed that
diastolic dysfunction may contribute to exercise capacity,
and a beneficial diastolic effect of cardiomyoplasty has
been demonstrated.30 On the other hand, investigators have
suggested that abnormalities in the periphery may contribute to
exercise performance in chronic heart failure.40
Thus, the increments of cardiac output and peripheral blood
flow could lead to an improvement in peripheral components,
including muscles. Regarding other factors, cardiomyoplasty did not
affect pulmonary ventilation in our study, and it did not
change neurohormonal activity and baroreflex sensitivity in patients
with heart failure.41 Further studies should be undertaken
to investigate the effects of cardiomyoplasty on parameters
determinants of exercise.
Study Limitations
This investigation is limited by the small
number of study
patients in a restricted 6-month follow-up period and the lack of a
comparable control group. However, at 6-month follow-up, most
conditioned muscle could be evaluated to determine cardiac effects. On
the other hand, in a longer mean follow-up, late muscle
degenerative changes after cardiomyoplasty were
demonstrated.42 The present study was limited in that
exercise LVEFs were not determined. Parameters of left
ventricular function measured at rest do not necessarily
reflect the most important feature of central
hemodynamicsthe ability to increase the
supply of oxygen to the metabolically active tissues, or
the reserve capacity of cardiovascular
system.43 However, methods for determining left
ventricular function reserve are not available for clinical
use, and difficulty in obtaining accurate measures during exercise
should be considered. Also, peak
O2 is
influenced not only by the subject's motivation but also by the
philosophy of the persons supervising the test concerning when the test
should be terminated.44 However, in the present study,
the same team supervised all tests. Our study did not include
cardiopulmonary exercise tests with on and off conditions
for the myostimulator. Differences between these conditions have been
reported concerning resting LVEF and hemodynamic data
after cardiomyoplasty.9 This issue should be addressed in
future studies.
Conclusions and Clinical Implications
Cardiomyoplasty is a
useful surgical method for improving NYHA
functional class and resting LVEF at 6-month follow-up. With regard
to exercise, the cardiomyoplasty may not have a significant impact on
peak exercise performance. However, cardiomyoplasty appears to
be able to improve peak
O2
in selected
patients with more restricted exercise capacity and, with the use of
selection criteria that include preoperative peak
O2, may be associated with
better
results concerning peak
O2.
Although
peak
O2 <14 mL/kg per
minute was found, this by no means represents an inflexible
guideline, and the ultimate decision to perform cardiomyoplasty should
be based on multiple parameters. Effects of cardiomyoplasty
on exercise capacity may be influenced by factors other than the
resting systolic cardiac effects resulting from the procedure.
Further studies should be performed to clarify the effects of
cardiomyoplasty on mechanisms determining exercise capacity in patients
with heart failure.
 |
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