Ann Thorac Surg 1999;67:489-493
© 1999 The Society of Thoracic Surgeons
Original Articles
Differences in intramuscular vascular connections of human and dog latissimus dorsi muscles
Daping Yang, MDa,
Steven F. Morris, MDb
a Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia, Canada
b Department of Surgery, Dalhousie University, Halifax, Nova Scotia, Canada
Accepted for publication July 13, 1998.
Address reprint requests to Dr Morris, Division of Plastic Surgery, Suite 4929, New Halifax Infirmary, Queen Elizabeth II Health Sciences Center, 1796 Summer St, Halifax, NS, Canada B3H 2A7
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Abstract
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Background. Distal ischemia and necrosis of the dog latissimus dorsi muscle flap used in experimental cardiomyoplasty have been reported. However, little information on the intramuscular vascular anatomy of the dog latissimus dorsi is available. It is unclear whether there are any anatomic factors relating to the muscle flap ischemia and necrosis, and whether the dog latissimus dorsi is a suitable experimental model.
Methods. To study the intramuscular vascular territories in the dog latissimus dorsi muscle, and to compare the intramuscular vasculature of the dog with that of the human, 5 fresh dog cadavers and 7 fresh human cadavers were injected with a mixture of lead oxide, gelatin, and water (200 mL/kg) through the carotid artery. Both the dog and the human latissimus dorsi muscles and neurovascular pedicles were dissected and radiographed. The intramuscular vascular anatomy of the latissimus dorsi muscles was compared.
Results. Radiographs demonstrate clearly that the pattern of latissimus dorsi intramuscular anastomoses between branches of the thoracodorsal artery and the perforators of posterior intercostal arteries in the proximal half of the muscle are different between the dog and the human. In the dog muscle, vascular connections between the thoracodorsal artery and the posterior intercostal arteries are formed by reduced-caliber choke arteries, whereas four to six true anastomoses without a change in caliber between them are found in the human muscle. The portion of the latissimus dorsi muscle supplied by the dominant thoracodorsal vascular territory was 25.9% ± 0.3% in the dog and 23.9% ± 0.5% in the human. For further comparison, an extended vascular territory in the latissimus dorsi muscle was demonstrated, including both the thoracodorsal territory and the posterior intercostal territories. The area of the extended vascular territory was 52% ± 0.5% of the total muscle.
Conclusions. The dog latissimus dorsi model may not be a perfect predictor of the behavior of the human latissimus dorsi muscle flap in cardiomyoplasty.
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Introduction
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The latissimus dorsi muscle flap has been experimentally and clinically transferred and stimulated to provide cardiac assistance in cardiothoracic operations [1–3]. Experimental studies have been performed mainly in dogs [4–6]. Some investigators recently noted distal ischemia and necrosis in the dog pedicled latissimus dorsi muscle flap used in experimental cardiomyoplasty [6–9]; however, the incidence of distal muscle ischemia in clinical cardiomyoplasty is not well known [9, 10]. The arterial supply to the human latissimus dorsi has been investigated [11–13], but little information on the intramuscular vascular supply of the dog latissimus dorsi is available [12, 14]. Because the dog is commonly used as an experimental model, this anatomic information is important. The purposes of this study were to investigate the intramuscular vascular territories in the dog latissimus dorsi muscle and to compare the intramuscular vasculature of the dog with that of the human.
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Material and methods
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Five mongrel dogs weighing a mean of 27.5 kg (range, 25 to 31 kg) were used in this study. The study protocol was approved by the Animal Care Committee of Dalhousie University, Halifax, Nova Scotia, Canada. Each animal was sacrificed and injected with a saturated mixture of lead oxide, gelatin, and water (200 mL/kg) through the carotid artery [15]. For comparison, 7 fresh human cadavers were perfused with the same mixture through the common carotid artery. Each specimen was cooled for 24 hours (4°C). Both the dog and the human latissimus dorsi muscles and all supplying vessels were dissected out and radiographed.
The radiographs were printed at the true muscle size as contact prints. The intramuscular vascular anatomy of the latissimus dorsi muscle was described by examining contact photographic prints of the radiographs. Because adjacent vascular territories usually were connected by reduced-caliber choke vessels, the intramuscular vascular territory of the thoracodorsal artery was delineated in the middle of the choke zones. Vascular connections between adjacent vascular territories were classified either as reduced-caliber "choke" anastomoses in which vessels gradually diminished in diameter or as "true" anastomoses in which the vessel continued between vascular territories at the same diameter. The area of the dominant vascular territory, the thoracodorsal artery, was traced on a transparent acetate sheet, and the paper template was cut and weighed (Mettler AE 50 balance, Fisher Scientific Limited, Canada) [16]. The percentage of the dominant vascular territory was calculated as follows: the weight of the template of the area of the dominant vascular territory was divided by the weight of the template of the entire muscle area and multiplied by 100%. The data were analyzed with the Student’s unpaired t-test, and p values of less than 0.05 were considered statistically significant. Values were expressed as means plus or minus standard deviations.
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Results
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In both the human and the dog, the latissimus dorsi muscle receives its blood supply from the dominant thoracodorsal artery in the proximal portion of the muscle, several segmental perforators of the posterior intercostal arteries in the midportion, and the lumber arteries in the distal portion (Fig 1). Radiographs demonstrate the presence of a large number of intramuscular arterial anastomoses in the three areas of the muscle (Fig 1). The intramuscular anastomoses between branches of the thoracodorsal artery and the perforators of the posterior intercostal arteries in the proximal half of the muscle are different in the dog and the human. In the dog muscle, vascular connections between the thoracodorsal artery and the posterior intercostal arteries are formed by reduced-caliber choke arteries (Fig 2A). In the human, there are four to six true anastomoses between the thoracodorsal artery and the posterior intercostal arteries (Fig 2B). The finding is consistent in all human specimens.
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Fig 1. Arteriograms of dog (A) and human (B) latissimus dorsi muscles. The muscle receives its blood supply from the dominant thoracodorsal artery (arrows) in the proximal portion of the muscle, several segmental perforators of the posterior intercostal arteries in the midportion, and the lumber arteries in the distal portion (dots).
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Fig 2. Angiograms showing differences in the intramuscular anastomoses of dog and human latissimus dorsi muscles (proximal portion). In the dog muscle (A), connections between the thoracodorsal artery and the posterior intercostal arteries are formed by reduced-caliber choke arteries (arrows). In the human muscle (B), the arrows indicate five true anastomoses between the thoracodorsal artery and the posterior intercostal arteries.
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The thoracodorsal artery in the dog latissimus dorsi muscle supplies 25.9% ± 0.3% (mean plus or minus standard deviation) of the muscle. There are several true anastomoses between the thoracodorsal artery and the posterior intercostal arteries. Thus, the anatomic boundary between the thoracodorsal and the posterior intercostal territories is determined in the middle of the true anastomoses between adjacent vascular territories, and the region of muscle supplied by the thoracodorsal artery in the human muscle is 23.9% ± 0.5%. There is no statistical difference in the dominant vascular territory between the dog and the human (p > 0.05). For further comparison, the dominant vascular territory in the human muscle was reapportioned, because of the difference in the intramuscular vascular anastomoses between the dog and the human. The extended vascular territory is shown with a dotted line defining the anatomic boundary in Figure 3. This territory includes both the thoracodorsal territory and the posterior intercostal territories combined by true anastomoses. The extended vascular territory is 52% ± 0.5% of the total muscle surface area.
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Fig 3. Angiogram demonstrating an extended vascular territory (above the dotted line) in the human latissimus dorsi muscle that contains both the thoracodorsal territory and the posterior intercostal territories combined by true anastomoses (arrows).
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Comment
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The latissimus dorsi muscle flap has been used extensively in reconstructive surgery, and also as an experimental animal model [16]. Its advantages include its large size, versatility, and reliability [17]. Since dynamic cardiomyoplasty was introduced in 1985 as a potential alternative to cardiac transplantation, the latissimus dorsi muscle has been considered the most suitable muscle for cardiac assistance [10, 18]. Although dynamic cardiomyoplasty is a promising form of surgical therapy for end-stage heart failure and can decrease a patient’s symptoms, objective hemodynamic effects have not been demonstrated [10]. The causes of cardiomyoplasty failure may include progressive muscle damage, which may result from the combined effects of chronic electrical stimulation, muscle ischemia, and loss of resting tension [10].
Several experimental studies have demonstrated distal ischemia of the latissimus dorsi muscle flap after flap elevation in the dog [6–9]. Carroll and colleagues [9] found that distal ischemic necrosis occurred in four of nine nondelayed dog latissimus muscle flaps, and that the distal necrosis contributed to complete muscle wrap rupture of the cardiomyoplasty. Therefore, they put forward a hypothesis that lack of significant change in hemodynamic variables in clinical cardiomyoplasty may be due to ischemia and necrosis of the distal part of the latissimus dorsi muscle flap [8, 9]. They concluded that vascular delay can improve latissimus dorsi muscle flap perfusion and function in the dog model, and that it may improve the clinical outcome of cardiomyoplasty [8, 9].
The neurovascular anatomy of the dog latissimus dorsi muscle previously was considered analogous to that of the human muscle [12]. In the present study, detailed anatomic data demonstrated differences in vascular anastomoses of the dog and human latissimus dorsi muscles. In the dog latissimus dorsi muscle, angiography revealed the presence of a "watershed" zone with reduced-caliber choke vessels between the territories of adjacent muscular arteries (Fig 2A). However, in the human muscle, the intramuscular arterial connections between the thoracodorsal artery and the posterior intercostal arteries were formed by four to six true anastomoses in the proximal half of the muscle (Fig 2B), and connections between the intercostal and lumbar arteries were formed by choke anastomoses and a couple of true anastomoses in the distal portion of the muscle (Fig 1B). This finding is similar to those described by Salmon [13] and by Taylor and Minabe [14].
Intramuscular vascular anastomotic patterns vary considerably. Taylor and Minabe [14] described arterial anastomoses and classified them as reduced-caliber choke anastomoses and true anastomoses. Choke anastomoses have been reported to be the most common type in both animals and humans [13, 14], whereas true anastomoses are uncommon in both animal muscles and most human muscles [14]. We are aware that the occurrence of the two anastomotic types within different human muscles is variable. Some muscles have well-developed vascular anastomoses between the vascular territories (ie, latissimus dorsi, rectus abdominis, gluteus maximus), whereas other muscles have less developed anastomoses (ie, rectus femoris). The variability also can be seen within individual muscles if the muscle is supplied by more than three vascular pedicles. For example, there are three vascular territories in the pectoralis major muscle.
Taylor and associates [19] reported that when a flap is elevated on a vessel at the base of the flap, at least one adjacent vascular territory usually survives without a prior surgical delay procedure. In general, attempts to capture (recruit) territories beyond the adjacent vascular territory result in vascular insufficiency [19, 20]. Ischemic necrosis of the distal portion of the dog latissimus dorsi muscle flap as reported by Carroll and colleagues [9] is an example of this concept. The beneficial effects of the delay procedure on flap survival are widely known. It has been demonstrated that a surgical delay may convert choke vessels between territories into true anastomoses so that more vascular territories can be captured [19, 20]. It is apparent from our previous studies that the length and area of flap survival depends on the dilatation of the choke anastomotic vessels within the flap and on the caliber and span of the adjacent captured arteries [21–23].
In the present study, we demonstrated that an extended vascular territory exists within the human latissimus dorsi that includes both the thoracodorsal territory and the posterior intercostal territories linked by true anastomoses (Fig 3). The extended vascular territory makes up 52% of the human latissimus dorsi muscle. It is likely that true anastomoses between vascular territories would augment capillary blood flow in the middle and distal regions of the latissimus dorsi muscle flap. Our recent experimental studies showed a correlation between muscle flap capillary blood flow and vascular architecture changes after a delay procedure in the canine rectus abdominis muscle and in the rabbit latissimus dorsi muscle flap model [24, 25].
This study showed that there are similarities and differences between dog and human latissimus dorsi muscles. The overall vascular supply is similar in dog and human latissimus dorsi muscles. However, most of the vascular connections between the thoracodorsal and posterior intercostal arteries are reduced-caliber choke anastomotic arteries in the dog, whereas in the human, they are true vascular anastomoses. This variation may influence the interpretation of cardiomyoplasty oriented research data derived from the dog latissimus dorsi muscle model.
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Acknowledgments
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The authors are grateful to Professor David Hopkins and Professor Robert Stone for their guidance, and for support provided by the Departments of Anatomy and Neurobiology and Surgery at Dalhousie University. We thank Mr Don Ferris and Mr Stephen Whitefield for their assistance with this project.
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References
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Abstract
Introduction
