Culshaw, Geoffrey

Love, Brian

Martinez-Pereira, Yolanda

Schwarz, Tobias

Thierry, Florence

English

This is the first report of an aortic sinus aneurysm with a communication to the main pulmonary artery, resulting in left-to-right shunting, diagnosed in vivo in a dog. A second left-to right-shunt through a patent ductus arteriosus was also present. Computed tomography angiography was used to confirm the presence of both congenital anomalies and assess the relative contributions of the two left-to-right shunts to left-sided volume overload

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TITLEAortic Sinus Aneurysm Communicating with the Main Pulmonic Artery, and a concurrent Patent Ductus Arteriosus, in a DogSUMMARYThis is the first report of an aortic sinus aneurysm with a communication to the main pulmonary artery, resulting in left-to-right shunting, diagnosed in vivo in a dog.  A second left-to right-shunt through a patent ductus arteriosus was also present.  Computed tomography angiography was used to confirm the presence of both congenital anomalies and assess the relative contributions of the two left-to-right shunts to left-sided volume overload.Keywords: Aortic sinus aneurysm, patent ductus arteriosus, computed tomographic angiographyINTRODUCTIONContinuous heart murmurs in puppies are always considered to be a significant clinical finding.  Most frequently they emanate from a left-to-right shunting patent ductus arteriosus (PDA) which significantly reduces life expectancy if left untreated, due to volume overload of the left heart resulting in left-side congestive heart failure (CHF) (Eyster et al 1976, Saunders et al 2014, Van Israël et al 2003).  Rarely, continuous murmurs may also arise from alternative intra- or extra-cardiac communications (Fujii et al 2009) that carry a similarly guarded prognosis.  The following case report describes a continuous heart murmur in a puppy, arising from two concurrent extra-cardiac shunts, firstly a connection between an aortic sinus aneurysm and the main pulmonary artery (MPA), and secondly, a left-to-right shunting PDA.  Both the aortic sinus aneurysm to MPA connection, and the combination of two concurrent left-to-right extra-cardiac shunts are extremely unusual.  This report demonstrates how advanced imaging techniques allow diagnosis of rare and complex cardiovascular anomalies in vivo, and the crucial role they play in clinical decision-making.  Such techniques permit assessment of the relative contributions to volume overload made by two separate but concurrent left-to-right extra-cardiac shunts, which aids treatment selection.CASE HISTORYA seven-month-old entire female Staffordshire bull terrier, weighing 15 kg, was referred for investigation of a heart murmur first detected at primary vaccinations.  Exercise intolerance and respiratory compromise had not been observed.  On presentation, dyspnoea was not evident and the respiratory rate was 36 breaths per minute.  On examination, mucous membranes were pink with a capillary refill time of less than two seconds.  Auscultation identified a regular heart rhythm at 130 beats per minute with a grade 5/6 continuous heart murmur loudest over the left heart base.  Femoral pulses were strong with no deficits.  Systemic blood pressure (oscillometry) was 158/67/99 mmHg (systolic/diastolic/mean).  On Doppler echocardiography the left ventricle and left atrium were mildly dilated (Table 1).  There was no evidence of significant systolic dysfunction, although definitive assessment is difficult in the presence of aortic to MPA shunts due to altered loading conditions (Spalla et al 2016).  Only mild aortic and mitral insufficiency was present.  The left aortic sinus was markedly dilated (Fig 1A).  Continuous wave spectral Doppler interrogation confirmed continuous flow (systolic 4.5 m/s, diastolic 3.4 m/s) through it, directly into the MPA (Fig 1B).  A second, smaller jet of continuous blood flow was also identified (systolic 2.0 m/s, diastolic 1.1 m/s) originating at the bifurcation of the MPA (Fig 1C), typical of a PDA, but directed towards the right pulmonary artery rather than the more usual direction of ductal flow towards the pulmonic valve (Boon 2011), but the ductus itself could not be visualised.  Its velocity was suspected to be underestimated due to difficulty aligning the interrogating ultrasound beam.  The tentative diagnosis was a left aortic sinus aneurysm with a communication into the MPA, and a second more distal communication between the descending aorta and MPA, most likely a PDA.Advanced imaging was used to confirm the morphology of this complex cardiac anomaly and, in particular, to assess the size and shape of the two left-to-right shunts in order to guide treatment options.  Continuous phase computed tomography angiography (CTA) images without ECG gating (Somaton Emotion, 16 slice, Siemens) were acquired under general anaesthesia (butorphanol premedication (Butador, Chanelle UK), propofol induction (Propoflo Plus, Zoetis), isoflurane (Iso-Vet, Chanelle UK) and oxygen maintenance).  This confirmed a dilated left aortic sinus with a short tubular connection, measuring 12 x 13 x 5 mm, to the MPA (Fig 2A & 3).  The left coronary artery was present and of normal size and morphology (Fig 2C).  A separate small PDA with a 1.3 mm ostium was also confirmed (Fig 2B).   The small size indicated minimal contribution to overall left-to-right shunting (Arlettaz 2017), and therefore closure of the PDA was not indicated.  There was no evidence of pulmonary oedema or pulmonary venous congestion.In the absence of clinical or CT evidence of CHF, no medications were prescribed.  To date, 12 months later, the patient remains free of exercise intolerance and tachypnoea, and the cardiomegaly has not increased on follow-up echocardiography.DISCUSSIONThis case report describes the first use of CTA to definitively diagnose a left aortic sinus to MPA communication in a dog, and assess its relative contribution to volume overload when a left-to-right shunting PDA is also present.  In people aortic sinus aneurysms develop when the media of the aorta and the annulus fibrosus of the aortic valve fail to fuse.  The right aortic sinus is most frequently affected while left aortic sinus involvement is very rare.  Young to middle-aged adults develop acute CHF when the aneurysm ruptures into the right ventricle or right atrium (van Son et al 1994, Webb et al 2005, Xin-jin et al 2013).  The right coronary sinus is also the predilection site in horses but the pathogenesis is less certain, with both acquired and congenital lesions reported (Marr et al 1998, Sleeper et al 2001).  The dog in this case report is typical of the few reported canine cases of aortic sinus dilatation or rupture in that, in contrast to people and horses, the left aortic sinus was involved (Abbott et al 1998, Jandrey et al 2005). To the authors’ knowledge there are no previous reports of definitive in vivo diagnosis of an aortic sinus aneurysm communicating with the MPA.  Abbott et al (1998) documented a ruptured left aortic sinus causing sudden onset weakness in an 18 month-old Dalmatian but dilatation of the aortic sinus was not described.  By contrast, in the dog of the current report, the young age at time of diagnosis and lack of acute clinical signs of pain that may be associated with rupture (Abbott et al 1998) suggest its aorticopulmonary connection was likely to be a congenital anomaly, but an initially intact aortic aneurysm that subsequently ruptured cannot be excluded.Jandrey et al (2005) reported a young adult Siberian Husky cross-breed with a blind-ending sac-like aneurysm that protruded, without rupture, into the left ventricular outflow tract, and originated via a narrow connection from a non-dilated left aortic sinus.  Aneurysm of the left coronary artery distal to the aortic sinus has been reported in two young German shepherd dogs, either with (Pelosi et al 2011) or without (Hernandez et al 2008) a communication into the MPA.  However in the patient of the current case report the left coronary artery was unremarkable on CTA.Jung et al (2012) described a two-year old Labrador retriever with a communication between a non-dilated left aortic sinus and the proximal MPA categorised as a type I (proximal) aorticopulmonary window.  This anomaly is thought to occur when the proximal truncal septum fails to develop and separate the foetal truncus arteriosus into the aorta and MPA (Mori et al 1978).  However, the dilatation of the aortic sinus of the dog in the current report would imply that the wall of the aortic sinus developed, albeit with abnormal architecture, rather than the truncal wall development was absent. Aortic aneurysms may also be part of a generalised soft tissue disorder in both dogs and people (Chetboul et al 2003, Isselbacher 2005) but generalised dilatation of the aorta, joint laxity and distortion of the ribs were not present in this case.  Furthermore, there were no clinical or echocardiographic findings in this dog to suggest the aorticopulmonary connection was acquired following erosion of the aortic sinus wall, such as with endocarditis, as has been previously described (Kleine et al 1966, Zani et al 2016).Aorticopulmonary communications result in flow of blood from the high resistance systemic circulation to the low resistance pulmonary circulation (Kittleson 1998).  This augments the normal pulmonary circulation returning to the left heart, in addition to the increased blood volume from activation of neurohumoral pathways such as the renin-angiotensin-aldosterone system.  If the volume overload of the left heart is sufficiently large it results in left-side CHF.  The left ventricular dilatation in this patient was consistent with volume overload and therefore, in the absence of significant mitral/aortic regurgitation or systolic dysfunction, indicated haemodynamically important left-to-right shunting.  In the normal heart, stroke volume from the right heart through the pulmonic valve approximates stroke volume from the left heart through the aortic valve, and these values can be calculated with Doppler and 2D echocardiography (Sanders et al 1983).  The ratio of pulmonic to systemic blood flow (Qp:Qs) can therefore be used to assess the magnitude of left-to-right shunting, with a ratio of greater than 1.5 considered clinically significant and an indication for occlusion of the shunt (Bussadori &Pradelli 2016).  However, Qp:Qs could not be measured in this case due to turbulent blood flow in the proximal MPA preventing acquisition of a clear spectral Doppler pulmonary flow envelope (Sanders et al 1983).  Additionally, Qp:Qs would not be able to distinguish the proportion of over-all shunting attributable to each of the two shunts. Both an an aortic sinus-to-MPA communication and a left-to-right shunting PDA were suspected on Doppler echocardiography but the turbulent blood flow in the proximal MPA made definitive identification and assessment of their relative contributions to volume overload difficult.  This was only achieved through CTA which demonstrated their location, morphology and size, and was crucial to the management of this case.  The magnitude of shunting through a PDA depends on its size (Armstrong 2005).  In people a PDA less than 1.5 mm is considered small and unlikely to allow clinically significant shunting (Arlettaz 2017, Fortescue et al 2010).  In this case CTA showed that the PDA was small, indicating minimal shunting, and that its closure was not indicated.   Had the PDA been larger then closure of the ductus by either surgical or interventional means would have been a relatively straightforward way of reducing volume overload and cardiac wall stress (Bureau et al 2005, Gordon et al 2010).  Thus, CTA confirmed that closure of the aortic sinus defect was required to significantly reduce volume overload.  Although CTA provided 3D imaging that would assist surgical planning, it also provided a visual representation of the challenges such surgery would entail.  Successful surgery involving aortic sinus aneurysms in veterinary patients is challenging and requires cardiac by-pass (Jandrey et al 2005).  Trans-catheter occlusion of the aortic sinus to MPA connection could also be considered (Javsicas et al 2010, Zani et al 2016) and the CT images in this patient would be invaluable in assessing its feasibility and the selection of a suitable occlusion device based on morphology of the aortic sinus defect.  However, such surgical and trans-catheter procedures, only available at a limited number of specialist centres, were beyond the owner’s financial constraints in this case.  In conclusion, this is the first reported use of CTA to diagnose aneurysmal dilatation of the left aortic sinus communicating with the MPA in a dog.  A concurrent PDA was also identified and complicated decision-making for management and treatment.  This case demonstrates how CTA offers a non-invasive means of imaging complex cardiovascular anomalies to answer clinically important questions, in this case the relative contribution to left-side volume overload of two separate aorticopulmonary communications. CONFLICT OF INTERESTNo conflicts of interest are declared.REFERENCESAbbott, J. A. & Porzio, P. (1998) Rupture of the left aortic sinus into the pulmonary artery in a Dalmatian dog. Veterinary Radiology & Ultrasound 39, 544-550Arlettaz, R. (2017) Echocardiographic evaluation of patent ductus arteriosus in preterm infants. Frontiers in Pediatrics https://www.frontiersin.org/articles/10.3389/fped.2017.00147/full [accessed 3 July 2018]Armstrong, F. A. (2005) Echocardiography. 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Aortic Sinus Aneurysm Communicating with the Main Pulmonic Artery, and a concurrent Patent Ductus Arteriosus, in a Dog

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Aortic Sinus Aneurysm Communicating with the Main Pulmonic Artery, and a concurrent Patent Ductus Arteriosus, in a Dog

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