38 - Optimizing Subcutaneous Implantable Cardioverter-defibrillator Placement: An Anatomic Study of Latissimus Dorsi Muscle and Long Thoracic Nerve Locations for Safety and Efficacy

Poster Board Number: 38
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Co-authors:

Peter Khalil - William Beaumont hospital Royal oak; Malli Barremkala, M.D. - Oakland University William Beaumont; Brian Williamson, M.D. - William Beaumont hospital royal oak; James Grogan, PhD - Oakland University William Beaumont

Abstract Body : Introduction



The primary objectives of the study were to assess the position of the anterior border of the latissimus dorsi muscle (LDM) and the location of the long thoracic nerve (LTN) to determine the optimal incision line for surgical placement of the subcutaneous implantable cardioverter-defibrillator (S-ICD). The S-ICD automatically delivers a shock to patients for sustained life-threatening arrhythmias and is implanted between the serratus anterior muscle (SAM) and the LDM. Despite the recommendation for an intermuscular implant technique utilizing a mid-axillary incision line, there is limited research describing this anatomical space to avoid complications. Variations in the positioning of the LDM pose challenges during device placement. The determination of the anterior border of the LDM facilitates the establishment of an optimal incision line for the implantation of the S-ICD generator, thereby providing improved guidance for implantation procedures. Additionally, the study delineated the location of the LTN relative to this space, which if transected, would lead to a winged scapula.

Methods



We examined 18 human donors at Oakland University William Beaumont School of Medicine; 12 (66.7%) were female donors averaging 80 years at the time of death (ranging from 53 – 97) and 6 (33.3%) were males averaging 78.6 years at the time of death (ranging from 66 – 99). We determined the position of the anterior border of the LDM by measuring the distance from the back to the anterior border of the LDM at the 5th and 7th rib levels (A). Additionally, the anterior-posterior width of the chest wall was measured (B). Finally, a measurement was taken from the back to where the LTN entered the SAM, noting the corresponding rib level.



Results



The mean distance for “A” was 7.6 cm (5.5 – 10.1 cm). The mean distance for “B” at the fifth rib was 21.4 cm (18.6 – 24.8 cm). The mean A/B ratio was 0.35 with a standard deviation of +/- 0.1 (range 0.27-0.45). This ratio didn't differ between genders.

On average, the LTN was running 0.7cm anterior to the LDM border at the 4th rib level, 0.3 cm posterior at the 5th rib, and 1.4 cm posterior at the 6th ribs level. The LTN entered the SAM at the 4th rib level in 6.6%, at the 5th rib in 46.6% and at the 6th rib in 46.6% of cadavers. The LTN did not extend caudal to the 6th rib in any specimens.



Conclusion



The anterior LDM border was variable and midaxillary line incisions might not be optimal for intermuscular implantations Our study also demonstrates the proximity of the LTN in comparison to the anterior LDM border, but in no specimens did the LTN extend superficial to the LDM caudal to the 6th rib. Caution should be taken when implanting S-ICD devices to avoid LTN injury.