Novel methods of myocardial protection and de-airing for complex descending aortic aneurysm surgery

Introduction

Surgery to the descending aorta is usually performed via a left thoracotomy. In re-operations or operations for the repair of very large aneurysms with significant (upward) longitudinal as well as transverse expansion, proximal and distal clamping of the aorta may be impossible. It may, therefore, be necessary to employ deep hypothermic circulatory arrest (DHCA) in order to facilitate repair. However, inadequate access to the ascending aorta makes myocardial protection difficult from a left thoracotomy. The essential use of cardioplegia to initiate diastolic arrest and provide adequate cooling of the heart during ischaemia led to the need to develop an unusual method of cardioplegia delivery.

Venting of the heart during cooling to prevent distension and subsequent de-airing of the heart, ascending aorta and arch (preferably with antegrade flow), as well as the descending aorta, was also required. A novel method of achieving both venting and antegrade de-airing is described, using a left atrial cannula and an unusual bypass circuit.

Case Study

A 64 year-old male who had previously undergone a mechanical aortic valve replacement 13 years earlier and replacement of his ascending aorta 5 years earlier, presented with a hoarse voice and an 8-cm aneurysm of his descending aorta. This contained a dissection flap and extended from the junction with the subclavian artery down to the lower third of the thoracic aorta. Tortuosity of the lower thoracic aorta and the high origin of the aneurysm made stent graft placement impossible. Due to both longitudinal and transverse expansion, the first part of the aneurysm sac was pushed upwards and filled the apex of the left chest cavity, making visualisation of the arch and clamping impossible through a left thoracotomy, as shown in Figure 1. For the same reasons, access to the pulmonary veins for venting was also not possible. Friable myocardium and difficult access also made venting of the apex an unattractive option.

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Figure 1.

Pre-operative CT scan showing an 8-cm aneurysm with dissection of the descending aorta and the expansion up into the apex of the left pleural cavity.

There was preserved left ventricular function, mild mitral regurgitation and atrial fibrillation, treated with warfarin, but no other past history. Routine pre-operative investigations were all normal.

A standard general anaesthetic was administered using a left-sided double lumen endobronchial tube. A spinal catheter was inserted at the L3-L4 vertebral level for cerebrospinal fluid (CSF) drainage if the pressure exceeded 10 mmH₂O. Further cerebral and spinal cord protection consisted of the administration of thiopentone 500mg, methyl prednisolone 500mg and magnesium sulphate 8 mmols 10 minutes prior to DHCA. Ten grammes of mannitol 10% was also added to the circulation at the onset of bypass and the head was packed in ice. Nasopharyngeal and bladder temperature probes and bilateral arterial and left internal jugular central venous catheter monitoring lines were inserted. Transoesophageal echocardiography was also used.

The cardiopulmonary bypass (CPB) circuit comprised a DLP 21Fr (left) femoral arterial cannula (Medtronic Inc., Minneapolis, MN, USA ), a 15Fr Biomedicus® cannula (Medtronic Inc.) inserted percutaneously into the superior vena cava via the right internal jugular vein (prior to positioning for thoracotomy) and a DLP 19Fr Biomedicus® cannula inserted into the inferior vena cava via the left femoral vein to give the best venous drainage. Once the left thoracotomy (4^th intercostal space) had been performed, a vent was inserted into the left atrial appendage and connected with a ‘Y’ connector to a vent/suction circuit and also to a side-arm of the arterial line. This limb was then clamped.

The CPB system consisted of an S3 roller pump (Stockert Instrumente GmbH, Munich, Germany), a Medos Hilite oxygenator (Medos Mediizinetechnik AG, Stolberg, Germany), a tubing pack (Chalice Medical, Worksop, UK), an AL8 arterial filter (Pall Corporation, New York, NY, USA) and a Vanguard cardioplegia system (Sorin Group, Mirandola, Italy). The CPB circuit was primed with 2 litres of compound sodium lactate solution (Hartmanns) including 10,000 IU heparin. Vacuum-assisted drainage was utilised to augment the venous drainage. Cell salvage was undertaken using the CATS system (Fresenius Kabi AG, Bad Homburg, Germany).

Limited dissection of the aneurysm was performed whilst the patient was cooled. When the temperature reached 15°C, DHCA was commenced. The descending aorta was opened and an 18Fr Foley catheter (Tyco Healthcare Ireland Ltd., Ballymoney, County Antrim, Northern Ireland) was placed under direct vision into the ascending aortic graft (Figure 2). The balloon was inflated with gentle pressure to just create a seal and 700ml of cold blood cardioplegia was administered through the Foley catheter at a pressure of 107 mmHg into the aortic root with a total flow of 340mL/min. The Foley catheter was then removed.

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Figure 2.

Diagram to show the bypass circuit and Foley catheter placement for cardioplegia delivery.

A 32-mm Hemashield tube graft with a single side-arm (Maquet, Sunderland, UK) was then sutured to the proximal and distal descending aorta using 3/0 Prolene and an inclusion technique to replace the aorta from the level of the subclavian branch down to approximately T9. A clamp was then applied to the lower descending aorta. To de-air the heart and proximal aorta, the vent arm of the left atrial cannula was clamped and the arterial side-arm unclamped to allow the slow pumping of blood up the vent and through the left atrial cannula, filling the heart and ascending aorta and allowing air to escape via the side-arm of the graft. Once all the air had been evacuated, the distal aortic clamp was removed and briefly placed across the graft, proximal to the side-arm. As bypass was slowly re-established via the femoral artery cannula, the lower portion of the graft was de-aired. The cross-clamp was then removed, the left atrial cannula reconnected as a vent and the side-arm of the graft oversewn. Total DHCA was 38 minutes.

Once the patient was fully warmed, cardiopulmonary bypass was discontinued, the cannulae were removed, haemostasis was secured and the wound was closed. The patient made a good recovery and was discharged home 9 days later with no neurological sequelae.

Discussion

Previous ascending aortic surgery and the presence of a very large descending aortic aneurysm with upward expansion into the apex of the left chest prevented central venous cannulation for bypass and access to the aortic arch for clamping. The combination of the initiation of DHCA via peripheral bypass and the administration of cardioplegia through a Foley catheter allowed adequate myocardial protection with better myocardial cooling (than with DHCA alone) and safe replacement of the descending aorta.

Foley catheter use has been described for temporarily sealing leaks during accidental rupture of major arteries and cardiac chambers. ¹ Although the concept of using an endoballoon to occlude an aorta and deliver proximal cardioplegia has been described in connection with minimally invasive cardiac surgery ² and in cases where, despite a median sternotomy, there is restricted access to the aorta, ³ to our knowledge this is the first description of a Foley catheter being used for cardioplegia delivery in this way, with placement under direct vision into the ascending aorta during open surgery of the descending aorta. Gentle and just occlusive balloon inflation by the surgeon during cardioplegia delivery avoided iatrogenic damage to the aorta. This technique proved simple to use, effective and considerably more cost effective than a purpose-designed endoballoon. This patient had already had a mechanical aortic valve and ascending aortic replacement, but the advantages of DHCA and Foley catheter use might also include avoidance of cross-clamping if the aorta is very calcified. ⁴

The second novel aspect of this technique involved the combined use of a left atrial cannula as a vent and a route for initial blood delivery during de-airing and re-establishment of the circulation after DHCA. De-airing retrogradely without a vent in the ascending aorta would have pushed air up into the arch and cerebral vessels. We avoided this by giving gentle antegrade filling with de-airing via the side-arm of the graft before re-establishing cardiopulmonary bypass with retrograde perfusion. This, too, proved an effective technique and was simple to arrange.