Discussion

Aortic dissection causes significant morbidity and mortality in adults, predominantly affecting men greater than 65 years of age. ^{Reference Larson and Edwards1} Risk factors for AD in adults have been widely studied and guidelines for treatment are well established. This is not the case in the paediatric population (i.e. age < 21 years), where the incidence of AD is low, ranging from 0.67 to 3.5% of all dissections. ^{Reference Fikar and Fikar2} As with adults, bicuspid aortic valve, connective tissue disease, and pre-existing aortic aneurysm are all predisposing factors, ^{Reference Fikar and Koch3} but CHD also plays a large role. In fact, in one of the largest retrospective reviews of AD in children and young adults (i.e. age < 30 years) to date, CHD was associated with AD 38% of the time. ^{Reference Shamszad, Barnes and Morris4} Complicating matters further is the fact that several forms of CHD are associated with moderate ascending aortic dilatation without a high incidence of dissection. ^{Reference Stulak, Dearani and Burkhart5} Therefore, with such different predisposing factors, it becomes unclear if adult treatment guidelines can be appropriately applied to children.

Aortic complications following orthotopic heart transplantation have also been documented. In adults, the incidence is estimated between 1 and 2%. ^{Reference Vigano, Rinaldi and D’Armini6} In children, the occurrence is significantly lower and is often associated with infection, aortic augmentation as part of staged Fontan palliation, or known connective tissue disease. ^{Reference Lang, Frazier and Collins7} In a review of 453 adults who underwent heart transplantation, Vigano et al found 9 (2%) who developed aortic complications, which they grouped into 4 categories: primary acute aortic rupture, bacterial and mycotic pseudoaneurysms of the ascending aorta, aneurysm and dissection of the native aorta, and dissection in heterotopic transplant. The aetiology of AD in the early post-operative period was related to systemic hypertension, size mismatch between the native and donor aorta, and technical errors in creating the anastomosis while true aneurysm and dissection of the native aorta was associated with atherosclerosis and immunosuppression-induced hypertension and diabetes.

In the absence of known bicuspid valve or connective tissue disease, the most recent ACCF/AHA guidelines recommend surgical intervention for thoracic aortic aneurysms exceeding 5.5 cm or growing at a rate of >0.5 cm annually. ^{Reference Hiratzka, Bakris and Beckman8} Our patient had slowly progressive ascending aortic dilatation for years which did not meet treatment guidelines by either criteria. Her transplanted aortic valve was trileaflet with no regurgitation, and she did not possess any other known predisposing risk factors for AD, such as family history, hypertension, or tobacco use. From a transplant perspective, she had no episodes of rejection, was never treated for a mediastinal infection, and does not have diabetes or hypertension, which are known side effects of long-term immunosuppression. Moreover, review of her operative records does not indicate that there was significant donor–recipient aortic mismatch. She was appropriately treated with an angiotensin-converting enzyme inhibitor, though this was discontinued due to concerns that her cough and wheezing were a medication side effect. Her ascending aortic diameter remained stable for several months despite stopping the enalapril, as was confirmed by aortic root angiogram, but a surveillance echocardiogram revealed a completely asymptomatic type A dissection 6 months after the catheterisation. In retrospect, the dry cough may have been due to compression of her bilateral main stem bronchi by the aortic aneurysm as opposed to a medication side effect.

Also noteworthy in this case is the patient’s homozygous MYBPC3 (3330+2T>G) gene mutation, which is known to cause lethal infantile hypertrophic cardiomyopathy. ^{Reference Zahka, Kalidas and Simpson9} It is possible that this mutation may also affect aortic integrity, but since death always occurs within the first year of life, this consequence may not have sufficient time to manifest. Alternatively, the patient may have a second homozygous recessive mutation or even de novo mutation for aortopathy, which is quite plausible given the high incidence of recessive disorders in the Amish population. However, the negative family history speaks against this when taking into consideration the large size of the patient’s family.

Post-anastomotic aortic dilatation is common in children after orthotopic heart transplantation, and cases of aortic aneurysm and dissection have been reported in both children and adults. However, our patient did not have any of the known risk factors for dissection in either the general or heart transplant population and developed this potentially life-threatening complication despite appropriate surveillance. This case suggests that children with known aortic dilatation status post-orthotopic heart transplant may be at increased risk of dissection and may require surgical intervention sooner than is recommended by the current guidelines.