The experimental study on the segmental resection of the heart is based upon the identification (Figures 1, 2) of the atrial (1) and of the ventricular anatomicosurgical segments (2, 3). The utilization of the favorable vascular distribution in some mammals of such a segmental arrangement for a systematized, controlled and planned partial resection is being tested in dogs aiming at the application of the successful experimental results to human beings. The beginning of the investigation yielded the first positive indications that the application of the findings might be possible in humans.
Fig. 1 - Diagram of the subdivision of the superior aspect of the human heart. The thirds of each quadrant contains the incidence of the atrial (segmental) arteries (Di Dio et al., 1972), corresponding to the anatomicosurgical segments of the atria. The segments and the arteries take their name from that of the third where the arteries originate. The most frequent atrial segments are (clockwise): 66% the right anterior medial (red), 52% the right anterior intermediate (yellow), 74% the left posterior medial (red), 52% the left posterior intermediate, 64% the left posterior lateral (red), 76% the left anterior lateral (red) and 62% the left anterior intermediate (red). The other segments are much less frequent.
Fig. 2 - Diagram of an ideal cross-section of the heart, at the ventricular level. Superior view. In each hemi-heart, the ventricular anatomicosurgical segments and intersegmental planes are indicated (Di Dio et al., 1983). There are three right ventricular segments: I DV, of the conus; II DV, right marginal and III DV, posterior interventricular. On the left there are four segments: I SV, anterior interventricular; II SV, lateral; III SV, left marginal and IV SV, posterior ventricular. MAIP and MPIP, median anterior and median posterior intersegmental planes; RAIP and LAIP, right and left intersegmental planes; LLIP, left lateral intersegmental plane; RPIP and LPIP, right and left posterior intersegmental planes.
MATERIAL AND METHODS
Three adult mongrel dogs (average weight: 15 kg) were studied. Anesthesia was induced with Nembutal (30 mg/kg, I.V.) and maintained with Ketamine (5 mg/kg, I.V.) as needed. Each animal was ventilated through a tracheal tube with 100% oxygen and Tidal volume of 15 MI/kg (Harvard 708, South Natick, MA). The dogs were placed in the right lateral decubitus position on the operation table and prepared for a sterile surgical procedure.
Through a left cervical incision, the jugular vein and the common carotid artery were dissected and catheterized. A polyethylene catheter for fluid infusion and a 7-F Sones catheter for cardiac catheterization were respectively inserted. EKG and blood pressure measurements were made through a Computer Software (ACQ Knowledge 3.01, Biopac Systems, Inc., Goleta, CA). The dogs received antibiotic treatment with Cephazolin 500 mg I.V. and Benzatin penicillin 1.200.000 UIM just before surgery.
The 7-F Sones catheter was introduced in the ostium of the left coronary artery for contrast injection (Urographine, Schering Lab.) to visualize the anterior interventricular branch and the circumflex branch. Subsequently, the right coronary artery was also catheterized for contrast injection.
In order to identify the left ventricular segments (Figure 2), a further injection into the circumflex branch was performed to selectively evaluate its blood supply to the left ventricle, especially aiming at its free wall, where we intended to recognize the segmental artery of the left marginal segment.
The chest was opened by means of a lateral thoracotomy (left 5th intercostal space). The pericardial sac was opened and retention sutures were placed to expose the heart. Simultaneously, a groin incision was performed for femoral artery dissection and cannulation. The CPB was established through the right atrium and femoral artery. Heparin (20.000 U) was given intravenously before cannulation. The CPB was carried out under moderate hypothermia (32°C).The heart was then lifted in order to identify the left marginal segmental branch previously seen by the catheterization procedure. An en bloc ligation of this selected left marginal segmental arterial branch and its satellite veins was performed at the level of the origin of the branch (Figure 3, arrow).
Fig. 3 - Dog nr. 3. The ischemic area is triangular and well demarcated. The en bloc ligature is indicated by an arrow.
Following the vessels ligation, there was a very clear demarcation of a triangular ischemic area, the base of which corresponded to the coronary sulcus.
The boundaries of that area were marked with electrocautery just prior to the intermittent aorta cross-clamping.
A deep incision was made along the limits, in order to resect and remove the ischemic area (Figures 4, 5).
Fig. 4 - Dog nr. 2. The ischemic area caused by the ligation of the segmental ventricular left marginal artery and veins is partially resected along its limits.
Fig. 5 - Dog nr. 2. The ventricular segment removed from the left ventricle, showing the segmental artery and the 2 satellite veins.
With the left ventricle cavity wide open, both papillary muscles were visualized, presenting a normal appearance.
The left ventricle cavity was closed with running absorbable suture (Figure 6). The air was vented through the ascending aorta and the animal was rewarmed to 37°C and weaned from CPB.
Fig. 6 - Dog nr. 2. Left marginal aspect of the left ventricle showing the suture between the boundaries of the resected segmental area (arrows).
The ribs were approximated with a double ligature after placing a drainage catheter in the left pleural space to evacuate fluid and air. The soft tissues were closed in two layers using absorbable running sutures.
After 4-6 hours of postoperative care, as the dog had a satisfactory spontaneous lung expansion and no air leak, the pleural catheter was then removed.
The animal was followed for a period of 7 days, and then evaluated through echocardiographic study and cardiac catheterization.
All animals received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health.
The animals had preoperative echocardiographic evaluation (Ultramark 4, Advanced Technology Laboratories, Bothell, WA) to confirm a normal left ventricle chamber. All examinations included 2-D and m-mode echo imaging of the heart from parasternal (short axis) and apical 4-chamber views using 2.5 and 5 mHz transducers appropriate for animal size. The Doppler study was performed to analyze a possible mitral insufficiency after the procedure (secondary to a dysfunction of the papillary muscles).
The echo was repeated every 2 days after the procedure to assess LV diameter and function.
The first dog remained hemodynamically stable after the surgical procedure. The echocardiogram showed an inferolateral akynesia and there was an impressive reduction in the systolic and diastolic LV dimensions. There was an ejection fraction within normal limits.
On the 4th postoperative day it was sacrificed. The heart was removed and the reconstructed LV was in a good healing condition.
The second dog also remained hemodynamically stable during the 7-day period follow-up. The preoperative echocardiogram showed normal LV size and function. The atrioventricular, the aortic and pulmonary valves were competent. After the segmentectomy there was also a large reduction (Figure 7) of the LV (systolic from 28 mm to 21 mm, and diastolic from 43 mm to 27 mm).
Fig. 7 - Dog nr. 2. Echocardiogram showing the significant reduction of the LV chamber dimensions, during systole and diastole pre and postoperative ventricular segmentectomy.
The LV shortening fraction (SF) was reduced from 35% to 21% and the LV ejection fraction (EF) was also reduced from 0.72 to 0.53, until the 4th postoperative day. On the 6th postoperative day there was an improvement on the LV function (EF = 0.72 and SF = 34%).
The Doppler showed a mild left atrioventricular valve (mitral) regurgitation.
The 3rd dog underwent a segmentectomy the resection of which proved to be too large. Although we weaned the animal from CPB with a high dose of inotropic support, the dog did survive for 4 hours. The reduction of the LV cavity was excessive because of an anatomical variation in the left coronary artery branching. In fact, the segmental artery was supplying almost the entire lateral wall.
Angiograms performed in each dog prior and after surgical procedure confirmed the reduction in the LV cavity, as demonstrated in Figure 8.
Fig. 8 - Dog nr. 2. Left ventricular angiograms showing the reduction of the LV chamber, during systole and diastole.
The results showed that the 1st dog segmentectomy did not prevent the normal function of the LV as the remaining walls compensated for the resected segment without impairing the ejection fraction. Taking into consideration that segmentectomy was being performed in healthy animals, the 2nd dog, similarly to the 1st one, there was no major problem with the ventricular function. The ligation of the segmental ventricular left marginal artery and veins led to a performance of a very large segmentectomy that removed a great portion of the LV. Such a large area corresponded to an anatomical variation of a segmental artery supplying more than the lateral margin of the LV. Such anatomical variation resulted in a close approximation of both papillary muscles provoking an excessive reduction in the diastolic volume, causing a low output syndrome. In spite of a massive inotropic support the animal died 4 hours after weaning from CPB.
The partial resection of the heart, especially of the left ventricle, has been a recent landmark in cardiac surgery, pioneered by BATISTA et al. (1996) (4,5). It opened new avenues for experimental investigation and applications in human patients.
As experience was being gathered with such an innovative approach, it stirred up controversy and many suggested a special selection of patients to be submitted to the recently presented surgical procedure (6,7). In addition, other authors established technical limitations and only particular myocardiopathies to take advantage of Batista's operation (8).
Major concerns on the widespread use of the partial left ventriculectomy from the technical and clinical standpoints are related mainly to cardiac arrhythmia (9,10)..
The availability of anatomical data on cardiac segments both atrial (1) and ventricular (2) and the well known successful results of segmentectomy in various organs, such as, lungs, kidneys, liver, spleen, led us to attempt to provide additional support to Batista's procedure by answering the widely voiced criticisms.
Instead of a partial ventriculectomy based upon the Laplace's law (4,5,11), we felt that the anatomical background provided by the cardiac anatomicosurgical segments might improve the surgical approach, technique and the results of the partial resection of the ventricle. Such a background allows for a planned, systematic and controlled resection of the cardiac ventricle, providing more flexibility to the surgeon, reducing hemorrhage and decreasing anesthesia as well as the time of surgery.
Toward this goal, an experimental investigation to validate our approach was carried out utilizing all supporting techniques for the anatomicosurgical segmentectomy of the canine left ventricle.
In order to secure the success of our procedure all the available means to surgeons were used. Particularly important was the coronary catheterization, which gave the mapping of the arterial segmentation, consequently indicating the origin of each segmental artery. The satellite veins running along each artery were also ligated en block with the selected segmental artery, providing a rapid ischemia and sharp limits for the ischemic area. Such a demarcation proved to be extremely helpful to make with precision the surgical incision on the myocardium with maximal saving of cardiac tissue.
As expected, the experiments proved the feasibility of the left ventricular segmentectomy in dogs, very likely in mammals.
The results so far widened the horizon of cardiac surgery and as usual, raised more questions to be answered with more scientific research.
It is hoped that with such an approach Batista's operation might become safer and allow for other surgical applications in the treatment of cardiomyopathies.
1. Experimental left ventricular segmentectomy, oriented by vascular ligation in adult healthy dogs, may be an important alternative to reduce the LV dimensions.
2. The left ventricular segmentectomy is possible with an en bloc ligature of a segmental ventricular artery and satellite veins.
3. The ventricular segmentectomy has the advantage of allowing systematic, controlled and planned resection of the ventricular wall, with a minimum hemorrhage and shorter time of surgery.
4. In the long range it is envisioned the application of single or multiple segmentectomy for the treatment of cardiomyopathy with dilated ventricle.
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