Page 20 - ANZCP Gazette November 2021

HEREDITARY HAEMORRHAGIC TELANGIECTASIA—ON BYPASS
Casey Edwards CCP, FANZCP
Patients with hereditary haemorrhagic telangiectasia (HHT) offer a unique set of challenges to the safe conduct of cardiopulmonary bypass. HHT, also known as Osler- Weber-Rendu disease is an autosomal dominant genetic condition. It is characterized by the presence of multiple arteriovenous malformations (AVMs) lacking intervening capillaries, resulting in direct connections between arteries and veins. The incidence of this disease is estimated to be 1:10,000 [1]. Clinically the most common manifestation of HHT is spontaneous nose bleeding, known as epistaxis. Severe epistaxis in cardiac surgical patients may result in preoperative anaemia, which is independently associated with adverse postoperative outcomes [2]. Another feature commonly observed in HHT is ‘spider veins’ – superficial telangiectases (small AVMs) on the lips, tongue, buccal mucosa, face, chest, and fingers. These telangiectases result from chronically dilated vessels causing elevated blotches on the skin. All small AVMs present a risk of rupture and bleeding during heparinised cardiac surgery as a result of both physical trauma and abrupt changes in arterial and central venous pressures on bypass, increasing the risk of intraoperative blood transfusion.
Larger, asymptomatic, central AVMs are also characteristic of HHT and present an even greater risk on bypass. Pulmonary AVMs are reported to occur in approximately 30–50% of affected individuals [1]. Shunting of air, thrombi or bacteria through pulmonary AVMs bypasses filtration capabilities of the lungs and may cause transient ischemic attacks (TIAs) or an embolic stroke. These risks are increased on bypass with the generally increased risk of embolic events [1]. Pulmonary AVMs also present a risk of rupture, which may result in intrapulmonary haemorrhage or haemothorax [3]. Literature suggests that spinal AVMs are less common than pulmonary, though they present the risk of paralysis with rupture or embolism and thus pose a major threat to patients’ postoperative quality of life [1].
Significant arteriovenous shunting of blood at any AVM location (or a combination of locations) predisposes patients to pulmonary hypertension [4]. A deconditioned right
ventricle from chronic pulmonary hypertension prior to cardiac surgery may increase surgical morbidity and mortality, further complicating the surgical course for patients with HHT [5].
There are several modifications to practice that can attenuate the surgical risks for HHT patients undergoing cardiac surgery. These modifications can broadly be subdivided into strategies to mitigate bleeding risk, and strategies to minimise embolic risk.
To reduce the potential impact of blood loss, preoperative optimisation of haemoglobin is important before elective cardiac procedures. Avoiding the use of intraoperative transoesophageal echocardiography if appropriate reduces the risk of physical trauma to AVMs in the oropharynx. Patients with severe epistaxis are better intubated orally than nasally to prevent physical trauma to the already vulnerable intranasal mucosa. Prophylactic nasal packing with gauze is also useful when epistaxis is severe. Pre- warming the endotracheal tube with sterile normal saline improves pliability to facilitate smooth intubation avoiding airway trauma [6]. On bypass, judicious administration of heparin to avoid unnecessarily high activated clotting times and avoiding hypertension are useful strategies to prevent rupture and excessive bleeding of AVMs. Postoperatively, using thromboelastography to avoid coagulopathy may also assist.
When considering the risk of embolization through central shunts, preoperative MRI may be of benefit. Information regarding the magnitude and location of AVMs may help clinicians evaluate a HHT patient’s risk, which can be communicated to the patient for an informed consent [1]. Standard bypass embolic precautions are especially important for patients with HHT, including the use of arterial line filtration (integrated or external), arterial line and cardioplegia line bubble detectors, prebypass filtration of prime fluids, using bypass tubing with a biocompatible coating, flooding the operative field with carbon dioxide for open-chamber procedures, frequent monitoring of ACTs and
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