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Communications to the Editor |

Possible Diaphragmatic Ischemia Following Harvesting of the Internal Mammary Artery FREE TO VIEW

Michael Poullis, FRCS
Author and Funding Information

Department of Cardiothoracic Surgery Hammersmith Hospital London, England



Chest. 1999;115(3):906-907. doi:10.1378/chest.115.3.906-a
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To the Editor:

Harvesting the internal mammary artery is a standard part of the majority of coronary artery bypass operations, but it is associated with an increased incidence of postoperative pulmonary complications.1 The use of bilateral mammary arteries increases this risk appreciably. Leaving the ipsilateral pleura unopened does not prevent collapse/consolidation development. The explanations vary, none of which truly explain the excessively high risk of collapse/consolidation after harvesting the internal mammary artery.

The internal mammary artery gives off two terminal branches: the superior epigastric and the musculophrenic. The musculophrenic artery runs around the costal margin of the diaphragm and supplies the lower intercostal spaces and the diaphragm. Thus, disconnection of the distal end of the mammary artery for coronary grafting may impair the blood supply to the diaphragm, intercostal muscles, and the phrenic nerve. The relatively ischemic diaphragm thus may not contract in response to stimulation of the phrenic nerve. A temporarily paralyzed diaphragm becomes flaccid and raised just as in phrenic nerve injury, and increases the chance of pulmonary collapse/consolidation. The ischemia is obviously only temporary until the preformed collaterals open up. Thus, the raised left hemidiaphragm after harvesting the left internal mammary artery may not be secondary to overlying collapse/consolidation or phrenic nerve palsy, but rather a primary event with collapse/consolidation being a secondary event.

The importance of the internal mammary artery was demonstrated in a swine model that is being developed for other experiments; it was utilized to demonstrate the extensive blood supply to the diaphragm. Crystal violet dye was injected into the left atrium, after the left internal mammary artery had been harvested and disconnected distally. The left hemidiaphragm demonstrated virtually no uptake of the dye, compared with the right side. Direct injection into the internal mammary artery resulted in the whole ipsilateral hemidiaphragm taking up the crystal violet dye virtually immediately (Fig 1).

Obviously the data are preliminary and could have been bolstered by phrenic nerve tests, local tissue oxygen saturation, nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide (reduced forms), ratios and videofluoroscopy of the diaphragms postoperatively. The aim of this small study was not to be exhaustive and comprehensive, but merely to draw the cardiac surgeon’s attention to another possible reason that pulmonary complications after harvesting the internal mammary artery may be due to diaphragmatic ischemia.

Now that the internal mammary artery is being used in pulmonary transplantation for bronchial artery revascularization, diaphragmatic complications could become more important in an already critical field.

Correspondence to: Michael Poullis, BSc, Department of Cardiothoracic Surgery, Hammersmith Hospital, DuCane Road, East Acton, London, W12 ONN; e-mail: mpoullis@rpms.ac.uk

Figure Jump LinkFigure 1.  Crystal violet staining of the diaphragm. Dark areas represent perfusion with crystal violet and pale areas represent relatively ischemic areas. Orientation: viewed from below, left hemidiaphragm uppermost, anterior to the left.Grahic Jump Location
Daganou, M, Dimopoulou, I, Michalopoulos, N, et al (1998) Respiratory complications after coronary artery bypass surgery with unilateral or bilateral internal mammary artery grafting.Chest113,1285-1289. [CrossRef]
 

Figures

Figure Jump LinkFigure 1.  Crystal violet staining of the diaphragm. Dark areas represent perfusion with crystal violet and pale areas represent relatively ischemic areas. Orientation: viewed from below, left hemidiaphragm uppermost, anterior to the left.Grahic Jump Location

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References

Daganou, M, Dimopoulou, I, Michalopoulos, N, et al (1998) Respiratory complications after coronary artery bypass surgery with unilateral or bilateral internal mammary artery grafting.Chest113,1285-1289. [CrossRef]
 
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