19 декабря 2001 00:00
Comparison of Ministernotomy with Minithoracotomy Regarding
ABSTRACT
Purpose: This prospective clinical study focuses on postoperative
pain and internal mammary artery (IMA) characteristics after
ministernotomy versus left anterior minithoracotomy.
Method: Patients were studied in two groups. Group A consisted of
267 consecutive single vessel (IMA to left anterior descending
artery (LAD)) minimally invasive direct coronary artery bypass
(MIDCAB) patients using ministernotomy from the tip of the xiphoid
to the fourth intercostal space. Group B consisted of the same
number of MIDCAB patients operated on through anterolateral
minithoracotomy. Pain was graduated using the visual analog scale
(VAS). Internal mammary artery (IMA) characteristics were compared
in both the groups.
Results: Postoperative pain was not significant statistically on
postop day (POD) 1 in either of the groups (p = 0.07). From POD 2
onwards Group A patients had less pain than Group B patients (p <
0.05), and the pain medication requirement from POD 2 onwards was
less in Group A than in Group B. Length of harvested IMA was 15.6 ±
2.1 cm in Group A as compared to 10.4 ± 2.2 cm in Group B (p <
0.05). Free flow of IMA in group A was 56 ± 16 ml/min., whereas in
Group B the flow was 50 ± 14 ml/min. (p = 0.04).
Conclusion: Compared to patients undergoing MIDCAB using
ministernotomy, anterolateral minithoracotomy patients suffer more
pain from POD 2 onwards and their postoperative pain medication
requirement is also higher. Length and free flow of IMA is better in
patients operated on for MIDCAB using ministernotomy. Thus,
ministernotomy is a better approach than minithoracotomy in terms of
postoperative pain and IMA characteristics for single-vessel MIDCAB
patients.
INTRODUCTION
Since the inception of coronary revascularization, coronary bypass
surgery on the beating heart has been practiced. With the advent and
evolution of the heart-lung machine and cardioplegia, the realm of
bypass surgery on a still heart expanded and beating heart surgery
took a backseat. With the recent interest in minimally invasive
procedures, the beating heart surgical techniques have been revived.
The minimally invasive direct coronary artery bypass (MIDCAB) has
been used primarily for grafting the left internal mammary artery
(LIMA) to the left anterior descending artery (LAD) through left
anterior thoracotomy, and has gained acceptance as a less invasive
option.
To combine adequate access with a smaller scar, less pain and
reduced respiratory discomfort as well as shorter hospital stay, the
ministerotomy approach has been proposed. We began using
ministernotomy approach for MIDCAB at the Escorts Heart Institute
and Research Centre in October 1998. The aim of the present study is
to present our experience with ministernotomy approach and a
comparison between ministernotomy and left anterior minithoracotomy.
PATIENTS AND METHODS
From October 1998 until December 1999, ministernotomy was performed
at our institute on 267 patients and compared with the same number
of patients operated on by left anterior minithoracotomy. Informed
consent was obtained from all the patients, and approval was
obtained from the institutional review board.
ANESTHESIA TECHNIQUE
All patients received tablet lorazepam and morphine sulfate
intramuscularly as premedication. Anesthesia was induced with
midazolam, fentanyl citrate, thiopentone sodium, and orotracheal
intubation was facilitated with vecuronium bromide. Anesthesia was
maintained with fentanyl and isoflurane in oxygen and intermittent
vecuronium. Hypothermia was prevented by use of warming fluids and a
warm water mattress. Monitoring consisted of pulse oxymetry,
capnography, ventilatory parameters, two-lead EKG (II and V5) with
ST trending, direct arterial pressure, pulmonary artery pressure,
segmental wall motion anomaly with transesophageal echocardiography
(TEE), and urine output and rectal temperature.
Patients were extubated when they met extubation criteria.
SURGICAL TECHNIQUE
Minithoracotomy
The patients are positioned supine with slight elevation of the side
to be operated. Left anterior thoracotomy is performed through the
fourth intercostal space (ICS) for LIMA dissection. In the initial
patients fourth left costal cartilage was excised to facilitate LIMA
harvesting, but this was abandoned subsequently.
The internal mammary artery (IMA) is always harvested under direct
vision. The Chestwall retractor or the Cardio Thoracic Systems (CTS)
(Cardio Thoracic Systems, Inc. Cupertino CA) or Genzyme stabilizer
system (Genzyme Surgical Products, Cambridge MA) is used to
facilitate IMA harvesting. A vertical incision is then made into the
pericardium and stay sutures placed. Traction on these sutures
elevates the heart into the incision, improving visualization of the
LAD. After administration of heparin sulfate (1.5 mg/kg), a 3−0
polypropylene suture with a silastic rubber bolster is placed
proximal to the target area on the LAD or right coronary artery
(RCA) to be bypassed. The internal mammary artery is prepared for
the anastomosis and local stabilization of the target vessel is done
either by the CTS or Genzyme stabilizer. The anastomosis between
LIMA to LAD is performed using two 7−0 polypropylene sutures
separately for the heel and apex. During anastomosis, the operating
field is kept clear of blood by blowing moist oxygen through a
sterile intravenous cannula. A pleural drain is placed and the wound
is closed in layers.
Ministernotomy
A vertical midline skin incision 6−8 cm in length is made starting
from the fourth intercostal space (ICS) to the tip of the xiphoid
process. The soft tissue overlying the sternum is mobilized and a
median sternotomy from the tip of the xiphoid process to the fourth
ICS is performed. If the sternum is very stiff, the lateral
extension of the sternotomy is done on the left or right side
depending upon which mammary artery is to be harvested, with the
help of an oscillating saw. The complete length of the IMA can be
harvested with the help of a long-tip electrocautery under direct
vision. Heparin (1.5 mg/kg) is administered, and the mammary artery
is divided distally and prepared for grafting. The pericardium is
incised vertically and heavy sutures are applied to elevate the
heart. Almost the whole length of the LAD can be visualized. An
appropriate site of the LAD is selected for the anastomosis and,
proximal to the site of the anastomosis, occlusion of the LAD is
done with a 3−0 polypropylene suture with a silastic rubber bolster.
If there are any hemodynamic or ECG changes, an appropriate-sized
intracoronary shunt is used to allow distal perfusion during the
anastomosis. Distal occlusion is never used. The local area is then
stabilized with a mechanical stabilizer (CTS or Genzyme) and an
arteriotomy is performed. A bloodless field is obtained with the use
of a blower. The internal mammary artery is divided proximal to the
bifurcation and prepared for the anastomosis. The mammary artery to
coronary artery anastomosis is performed with a running 7−0
polypropylene suture. The IMA pedicle is tacked to the epicardium
after completion of anastomosis, and a trough is cut in the
pericardium to prevent kinking of the IMA pedicle. Hemostasis is
ensured. A chest tube is then placed in the pericardium well
extending into the pleura, or a separate chest tube is placed in the
pleura.
Assessment of Surgery
In both minithoracotomy and ministernotomy, patency of the graft is
assessed by Doppler flow prior to the chest closure, and angiography
is performed on the fourth postoperative day.
Pain was assessed with a visual analog scale (VAS) score on a scale
of 0 to 10, with 0 referring to no pain and 10 referring to
unbearable pain. The patients had been instructed in the use of the
scale preoperatively. Postoperatively, after endotracheal
extubation, the VAS score was noted every two hours for the next 12
hours, and thenceforth every four hours until the fourth
postoperative day. Scores were recorded by independent nurse
observers who were blinded to the technique used. All analgesic
dosages were administered based on the VAS score, as noted by
blinded nurse observers. After endotracheal extubation, analgesia
was provided with 30 mg of intramuscular ketrolac tromethamine
(Ranbaxy Labs, Delhi, India). The need for the initial dose and
repeat dose in either group was determined by a VAS score of 6 or
more.
Free flow of the IMA was measured after harvesting and dividing the
distal end of the IMA. The internal mammary artery was allowed to
flow freely in a bowl for 30 seconds and the amount of the blood
collected is measured. The length of the harvested IMA is measured
with the help of black silk thread.
STATISTICAL ANALYSIS
The Student's t-test was applied for continuous variables between
the two groups. Comparison of categorical variables between two
groups was conducted using cross tables with Pearson's Chi-Square
test if expected values were small, and the Fisher exact test was
used if the expected values were high. A p value of < 0.05 was
considered statistically significant.
RESULTS
Preoperative patient characteristics are shown in Table 1. There was
no statistically significant difference in preoperative patient
parameters. Preoperative risk factors are depicted in Table 2 [see
Table 2]. Of patients older than 70 years, 56 (20.97%) were in the
ministernotomy group and 52 (19.47%) were in the minithoracotomy
group. Forty-eight patients (17.97%) in the ministernotomy and
forty-two patients (15.73%) in the minithoracotomy group had left
ventricular ejection fractions (LVEFs) below 30%. These factors did
not reach statistical significance.
During anastomosis, six patients in the ministernotomy group and
four patients in the minithora-cotomy group had ST elevation in
chest leads without any hemodynamic instability or regional wall
motion abnormality on TEE. In all these patients, ECG changes
reverted to normal on completion of the anastomosis and release of
the snare and the bulldog clamp applied on the LIMA. However two
patients in the ministernotomy group and three patients in the
minithoracotomy group had hemodynamic instability with regional wall
motion abnormality on TEE along with ECG changes, which required
conversion to full sternotomy and cardiopulmonary bypass (CPB).
The harvested LIMA was significantly longer in ministernotomy
patients than in patients operated on through minithoracotomy [see
Table 3]. None of the patients required IMA extension in the
ministernotomy group. In the minithoracotomy group, four patients
required IMA extension; the inferior epigastric artery (IEA) was
used for the IMA extension in one patient and the reversed saphenous
vein was used in three patients.
Postoperative results and clinical outcome are presented in Table 4.
More ministernotomy patients than minithoracotomy patients were
extubated in the operating room. Total blood loss was greater in
patients operated on through ministernotomy than in minithoracotomy
patients (p < 0.01). This may be due to more loss of blood from the
sternotomy.
A postoperative Doppler flow study of LIMA-to-LAD was performed on
all patients. Diastolic flow was excellent in 264 ministernotomy
patients and in 263 minithoracotomy patients. However, there was no
diastolic flow in three ministernotomy patients (1.12%) and four
minithoracotomy patients (1.49%), which was confirmed on
angiography. One hundred and ten patients in each group underwent
postoperative angiography during their hospital stay, and the LIMA
was found to be patent in all patients except those mentioned above.
One patient in the ministernotomy group and two patients in the
minithoracotomy group required reoperation, for which the radial
artery was used as a conduit.
The mean VAS scores for the first 12 hours were not different
statiscally in both groups but did not reach statistical
significance except at the first two hours [see Table 5]. From
second postoperative day (POD) onwards pain was significantly
greater in patients operated on through minithoracotomy as compared
with ministernotomy (p < 0.05) [see Figure 1]. By the time of
discharge, pain levels had decreased in almost all the patients.
The mean postoperative ketorolac requirements were found to be lower
in the ministernotomy group (32.57 ± 14.67) than in the
minithoracotomy group (48.27 ± 18.42), a difference that was found
to be statistically significant (p < 0.05).
One patient in each group (0.37%) died during hospital stay. The
patient operated on through ministernotomy had acute renal shutdown,
and the minithoracotomy patient experienced massive gastrointestinal
bleeding following surgery.
(256 of 267 patients) in the ministernotomy group and 94.38% (252 of
267 patients) in the minithoracotomy group. Two hundred and fifty
patients in the ministernotomy group and 248 patients in the
minithoracotomy group were in functional class I and had good
diastolic flow on Doppler flow evaluation of the mammary coronary
anastomosis. Six patients in the ministernotomy group and four
patients in the minithoracotomy group are in angina class II and are
on medical therapy.
DISCUSSION
Less invasive procedures for surgical revascularization are being
proposed as a means of reducing operative trauma and the sequel of
cardiopulmonary bypass (CPB) [Westaby 1996, Coulson 1998a]. These
new techniques attempt to reduce surgical trauma and thus
postoperative pain, and give better cosmetic results. By avoiding
CPB, cerebrovascular, renal, and bleeding complications are
significantly reduced. However, not all minimally invasive coronary
operations are performed with reduced surgical trauma. Lateral
thoracotomies can be quiet painful even if small in length. The
thoracotomy approach, due to trauma to costal cartilages, may induce
more pain than that resulting from a median sternotomy [Heres 1998].
Intercostal nerve injury can cause very significant pain, chest wall
splinting, hypoventilation, and respiratory compromise. Complete
mobilization of the IMA through a limited thoracotomy is difficult
and time-consuming.
By moving away from sternotomy, MIDCAB surgeons have revisited the
known problems of thoracotomy and the side effects of pain
management. In order for less invasive cardiac procedures to become
universally accepted by surgeons and patients alike, refinements are
needed.
Coulson et al. [Coulson 1998b] have described an alternative
technique, the «T-MIDCAB» procedure. By grafting a short segment of
radial artery or saphenous vein between the undisturbed IMA and
target coronary artery, complete thoracotomy is avoided and chest
wall retraction and perioperative pain are minimized. This
procedure, however, is technically more demanding and requires an
additional anastomosis between the donor vessel and the IMA.
The median sternotomy was originally described by Milton in 1897 and
was popularized by Jullian in 1957 [Jullian 1957]. It eventually
became the universal method of exposure for most cardiac procedures.
Surgeons quickly realized that median sternotomy provided good
exposure to every region of the heart, the great vessels, and the
mediastinum. As its frequent use attests, surgeons are comfortable
with the median sternotomy because of the exposure of cardiac
structures that it provides. Until recent years, concerns about
wound trauma and the final appearance of the surgical scar were a
low priority. However, now that the minimally invasive and
«off-pump» surgeries have become widely practiced, other
considerations are surfacing. Cosmetic disadvantages of the full
median sternotomy are obvious – a large and visible scar that
remains a permanent reminder of an otherwise low-risk procedure. The
safety advantages of reduced surgical trauma remain a cardinal
feature of all the modified techniques.
Several alternatives are currently available for accessing the
thoracic cage that achieve adequate access with a smaller scar, less
pain, and reduced respiratory discomfort as well as shorter hospital
stay. We have used lower ministernotomy primarily for grafting the
LIMA to the LAD from the tip of the xiphoid process to the fourth
ICS. To create the exposure for harvesting the IMA and for the
subxiphoid approach, we have used the Rultract retractor (Rultract
Inc., Cincinnati, OH) for providing vertical lift of the lower
sternal bone [see Figure 2] or we used the same Genzyme (Genzyme,
Inc., Cambridge, MA) retractor that we used for local stabilization
of the heart. A simple upward tilt exposes the IMA, which can be
easily harvested. Complete visualization of the IMA as well as the
LAD is achieved with great ease. In our study, the length of the
harvested IMA was significantly longer in ministernotomy than in
minithoracotomy. In minithoracotomies, the length of the harvested
IMA is a great limiting factor; at times it may be very difficult to
harvest even a few centimeters more, especially in a laterally
situated LAD.
These results are achieved without debilitating musculoskeletal
trauma. In addition, conversion to either an extended transverse
incision or a standard median sternotomy can be done anytime that
the need arises. All of these advantages are limited if surgery is
done through minithoracotomy for a LIMA to LAD anastomosis.
Another advantage of ministernotomy for IMA harvesting and LIMA to
LAD anastomosis is the lower learning curve as compared with the
minithoracotomy approach. The same technique is used for IMA
harvesting and for the anastomosis as in the standard median
sternotomy approach.
The port access system (Heart Port, Inc., Redwood City, CA), which
has also been used for coronary artery bypass grafting (CABG) by
some surgeons [Ribakove 1998], has the advantage of a limited
incision while still providing the comfort to perform the
anastomosis on an arrested heart in a bloodless surgical field.
Factors that limit this technique are the necessity of establishing
extracorporeal circulation through femoral vessels and placement of
the endoaortic clamp, in addition to the additional expenses for
special instrumentation and the cardiopulmonary circuit kit.
assistance are also employed for minimally invasive CABG operations,
but these techniques are quite expensive, require special training
and are highly operator-dependent, and are not easily reproducible.
In the lower partial ministernotomy approach, the upper part of the
sternum and the sterno-clavicular and manubriosternal joints are not
disturbed, so the chances of sternal dehiscence are low, especially
in elderly patients and those with chronic obstructive pulmonary
disease (COPD). Because the chest is not widely opened, there is
less risk of traction injuries to the brachial plexus. In addition,
the smaller incision and lower wound morbidity yield a more
acceptable cosmetic result for patients [see Figure 3] In our series
we did not observe any sternal wound dehiscence in patients operated
on by ministernotomy.
It may be claimed that for single vessel disease, percutaneous
transluminal coronary angioplasty (PTCA), with or without stenting,
is the treatment of choice. The data from randomized studies
comparing PTCA with CABG consistently showed a similar incidence of
death and myocardial infarction at one, three, and five years after
PTCA and CABG [Pocock 1995, BARI 1996]. Both treatment modalities
were equally effective in relieving angina [Pocock 1995]. The angina
relief, however, is achieved in patients treated with PTCA at the
cost of a significantly higher need for repeat revascularization
during the first year [Pocock 1995, BARI 1996]. Obviously, PTCA does
have its own intrinsic limitations. At the same time, significant
improvements in CABG techniques are being made, which renders PTCA
and CABG complementary rather than strictly exclusive techniques,
especially in high-risk patients for whom a combination of the
techniques (hybrid revascularization), may be more effective. We
performed hybrid revascularization in eight patients (2.99%) in the
ministernotomy group and in six patients (2.24%) in the
minithoracotomy group, for whom complications included diffusely
diseased atheromatous aorta and impaired renal function. One of the
limitations of PTCA is that the device must cross the target lesion
in order to perform its specialized function. In patients with
chronic totally occluded arteries, distal lesions, and tortuous or
small coronary arteries, and patients with complex type C lesion(s),
this is particularly challenging. These patients are difficult to
treat despite improvements in catheter technology (guide-wire
design, balloon profile and material, and laser technology) [de
Jaegere 1997]. Another limiting factor for PTCA is late luminal
renarrowing or restenosis, which imposes a significant medical and
financial burden on the patient. In our series, 42 patients (15.73%)
required MIDCAB following PTCA in the mini-sternotomy group and 38
patients (14.23%) in the minithoracotomy group.
Perception of pain is individualized. Nevertheless partial
quantification of these subjective symptoms can be provided by the
use of scoring systems [Westin 1997], which provide a framework for
comparing the two approaches. In our series, on the first POD, pain
was found to be the same in both groups, but on subsequent days pain
was significantly greater in patients operated on through left
anterior minithoracotomy. Stretching of the intercostal nerves,
muscles, and parietal pleura may be the a contributory factor for
the greater pain in the thoracotomy group. In the median sternotomy,
once the sternum is approximated and there is no sternal
instability, there is not much pain. Since the entire sternum is not
incised, patients operated on through partial sternotomy do not
experience significant pain and muscular tension in the back.
Adequate pain control is one of the important considerations for
MIDCAB and is essential for reducing the length of stay in ICU and
the hospital. Severe pain is know to cause reduction in respiratory
mechanics and mobility, and to increase sympathetic hormonal and
metabolic activity [Sabanathan 1990]. If pain relief is not adequate
after MIDCAB surgery, then all its advantages may be negated due to
the adverse effects of postoperative pain. Various analgesic
techniques are used after MIDCAB, which include nonsteroidal
intrapleural analgesia, and thoracic epidural analgesia [Mehta
1998]. In our series, the nonsteroidal anti-inflammatory agent
ketorolac was found to provide adequate pain control
postoperatively, although the analgesic requirement was greater in
the minithoracotomy group.
In conclusion, in terms of post operative pain and IMA
characteristics, significant differences can be seen between the
results of left anterior minithoracotomy and ministernotomy. From
the first POD onwards, patients having a ministernotomy perceive
less pain, and the significantly longer IMA in ministernotomies can
be a major advantage over minithoracotomy. Conversion to standard
median sternotomy from a ministernotomy is much easier should the
need arise, and the procedure has a shorter learning period for the
surgeon and does not require specialized instrumentation.
AUTHOR/ARTICLE INFORMATION
Presented at the Third Annual Meeting of the International Society
for Minimally Invasive Cardiac Surgery, Atlanta, Georgia, June 8−10,
2000.
Address correspondence and reprint request to: Dr. Rajneesh
Malhotra, Escorts Heart Institute and Research Centre, Okhla Road,
Fax: 0091−11−6825013, Email: malhotrarajneesh@hotmail.com ;
ehirc@vsnl.com
Keywords: coronary bypass, ministernotomy, minithoracotomy,
postoperative pain, MIDCAB, LIMA, LAD.
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