A Ten Year Retrospective Study on Cor Triatriatum Sinister Associated Heart Failure in Dogs

Cor triatriatum sinister and dexter occur from a fibrous membrane dividing the left or right atrium, respectively, resulting in a “heart with three atria”.  Cor triatriatum sinister (CTs) is a rare defectin dogs and cats, that arises when the common pulmonary vein fails to regress normally, resulting in a fibrous membrane that persists within the left atrium, dividing the left atrium into two subchambers (Oliveira et al., 2011; Menaut et al., 2009). In CTs, the left auricle has two distinct compartments, the proximal one that receives blood from pulmonary vein and the distal compartment communicates with the left ventricle through mitral valve. One or more small orifices that are present on the intra atrial separating membrane allows communication between these two compartments (Cote et al., 2011). CTs is documented to be a result of lack of normal regression of the fetal pulmonary veins to form the roof of the left atrium (Lima et al., 2010). One or more small orifices present in the intra-atrial separating membrane allows the communication between both the compartments of the left atrium (Oliveira et al., 2011). The proximal, high-pressure subchamber receives pulmonary venous return, while the distal, low-pressure subchamber is adjacent to the mitral valve and contains the left auricular appendage. The malformation and its hemodynamic consequences can be diagnosed with the help of 2d-echocardiography (Castagna et al., 2019).  Inspite of palliative medical management, complete surgical excision of the membrane is the definitive treatment protocol that is commonly recommended in all symptomatic human patients (Bruce, 2015). The aim of this study was to place on record about this most unusual condition (resulted in heart failure) that was sporadically reported among veterinary patients.

The present investigation was carried out among the dogs that were suspected for cardiac ailment and presented to cardiology ward of Veterinary Clinical Complex, CVSc Rajendranagar and those referred from various private clinics, for a period of 10 years (2012 to 2022). Almost all these dogs were showing the signs of heart failure of varied intensity and were subjected to a detailed clinical examination such as, recording temperature, pulse and respiration followed by physical examination. Chest auscultation was carried out in a sound proof environment, on specific points at left and right cardiac region. Thoracic plain radiograph was taken on both the right lateral and ventro dorsal views. Further, 2d-echocardiographyand colour doppler studies were performed on Mindray Z5Vet Ultrasound machine, using 6C micro convex probe to diagnose various cardiac diseases and specifically to confirm cortriatriatum sinister (CTs) in these dogs. Both short and long axis of cardiac chambers was evaluated to detect the cardiac anomaly on B-mode and dimension of the left ventricle was evaluated on M-mode echocardiography. Later Doppler evaluation of CTs dogs was also carried out to study the abnormal blood flow. These dogs were medically managed with angiotensin converting enzyme inhibitors (ACEi), diuretics and positive ionotropic drugs.

2dimensional echocardiography was performed in right lateral recumbancy as right parasternal transthoracic echocardiograms in non-sedated dogs suspected for CTs. Access to the right side of the thorax was facilitated by using a table with a special cut-open to allow the transducer to be directed upward towards the site of maximal cardiac pulsation (Allworth et al., 1995). Transducer is located parasternally between right third and sixth intercostal spaces between sternum and costochondral junction (Thomas et al., 1994). M-mode recordings were taken at the high papillary level and themeasurement of left ventricular dimension at end–diastole (LVEdD) and end-systole (LVEsD) was made intraluminally from the trailing edge of the septal wall image to the leading edge of the ventricular free wall. End-diastolic and end–systolic measurements of the thickness of the Inter Ventricular Septum (IVSd, IVSs) and left Ventricular Posterior Wall (LVPWd, LVPWs) were made using trailing edge (AllWorth et al., 1995). Further, colour flow Doppler was also done to assess the directional flow as per the technique suggested by Dominique and Marc-Andre (2008).

Occurrence of CTs
 
During the present investigation, a total of 795 dogs were diagnosed for various acquired (89%) and congenital cardiac diseases (11%), accounting for 708 and 87 cases, respectively. Out of the total congenital diseases (87), cortriatriatum sinister (CTs) was diagnosed in 4dogs (4.59%), aged between 5-7 years  amongst Boxers (2), Doberman (1) and Cocker spaniel (1) breeds. Congenital anomalies of the cardiovascular system are defects present at birth and often lead to perinatal death in dogs. However, in some cases, congenital heart diseases (CHDs) are asymptomatic and undetected until later in life, so the percentage of dogs with congenital heart diseases that survive to adulthood to breed can be rather high (Garncarz et al., 2017 and Caivano et al., 2018). Bulldog and Boxers are reportedly common affected breeds (Gustavo et al., 2012). The difference in the prevalence of CHDs depends on the popularity of the breed in a country in a given period of time (Ghirlanda et al., 2014). Knowing the epidemiology of CHDs plays an important role in maintaining dog health and in preventing the diffusion of CHDs in the dog population (Garncarz et al., 2017). Cor triatriatum is among the rarest developmental anomalies of cardiovascular system reported in humans (Hamdan et al., 2010) followed by dogs and cats (Cote, 2011). Cor triatriatum can be either, sinister or dexter that result from a fibrous membrane dividing the left or right atrium, respectively. Cor triatriatum dexter (CTd) is thought to account for only 0.1% of human congenital heart disease and only 0.3% of canine congenital heart disease (Bruce, 2015). While CTd has been well described in the dog, historically, CTs was first described in human beings (Church, 1868) and later after more than a century in the veterinary patients. The first ever case was reported in a cat (Gordon et al., 1982). Among dogs, cortriatriatum dexter  has been reported earlier (Tobias et al. 1993; Kittleson, 1998; Mitten et al., 2001; Oliveira et al., 2011) and CTs quite recently (Gustavo et al., 2012).
 
Clinical presentation of CTs
 
All the dogs diagnosed for CTs were presented with similar history and signs suggestive of heart failure viz., exercise intolerance, dyspnoea at rest, cough- particularly dry nocturnal type that was ignited by physical activity and deep sleep, generalised weakness. Syncope was additionally reported in the Cocker spaniel. Physical examination revealed,a considerably elevated heart rate and  a femoral pulse that was regular, strong and synchronous to the heart beats. Auscultation revealed a soft systolic murmur on left heart base (75%), tricuspid area (50%) and pulmonic valve area (25%), withmoderately distended jugular vein (50%) and jugular pulse (50%). The details are given in Table 1.  Rectal temperature was within the normal range among all the affected cases, slightly pale conjunctival mucous membrane. The averagesystolic arterial blood pressure that was recorded among these dogs, using Doppler blood pressure (BP) machine was 145 mm Hg. Mild neutrophilia, normal BUN and serum creatinine values were observed. Radiographic abnormalities noticed on right lateral thoracic radiograph included cardiomegaly, increased sternal contact, elevated trachea, pulmonary congestion and engorged caudal vena cava (Fig 1). Though cortriatriatum sinister is a well-documented cardiac malformation among humans, published reports  amongst canines  are rare (Castagna​ et al 2019). CTs affected dogs and cats are presented with the signs of left heart failure, with pulmonary edema, pleural effusion, or both (David, 2016). The pathophysiology and complications of CTs are variable and depends whether it is an isolated defect or associated with other cardiovascular anomalies, including the size of the membrane’s orifice (Kelmendi et al., 2009). If the anomalies remain associated with other cardiovascular defects or if the foramen is too large, the  prognosis might be serious (Nassar and Hamdan, 2011; Lima et al., 2010; Sandra, 2020).




 
Echocardiographic features of CTs
 
Right parasternal 2d-echocardiography revealed a left atrium that was subdivided by a transverse membrane into two distinct compartments, one proximal and one distal, thus confirming the cortriatriatum sinister (Fig 2). Dilatation of right atrium, right ventricle and thickened right interventricular septum with normal interatrial septum were also noticed (Fig 3 and 4). The mitral valve did not reveal any abnormality, but billowing of the tricuspid valve was noticed (Fig 5).  Pulse wave Doppler at mitral area showed laminar flow and regurgitant flow with turbulence jet was seen at the tricuspid valve area (Fig 6 and 7). Mild pulmonary valve regurgitation was also noticed on the right parasternal 4-chamber short-axis view. The presence of obstructive membrane in the left atrium leads to increased pulmonary venous capillary pressure resulting in pulmonary edema, congestion and pulmonary hypertension (Gordon et al., 1982; Oliveira et al., 2011). 2d-echocardiography is the most promising procedure to confirm the anomaly (Thakrar et al., 2007; Nassar and Hamdan, 2011; Menaut et al., 2009). As the disease progress, subsequently there will be enlargement of left proximal atrial chamber and main pulmonary artery, thereby resulting in dilatation of right atrium and right ventricle resulting in eccentric hypertrophy (Cote et al., 2011).












 
Management of HF associated with CTs
 
Following treatment with diuretic (frusemide), ACE inhibitor (benazepril) andinotropic agent (pimobendon), all the CTs dogs showed improvement in overall physical activity from day 10. There was alleviation in dyspnoeathat improved to near normal breathing pattern, absence of cough, improvement in physical activity, energy levels with  exercise tolerance levels and normal appetite by day 20, following therapy. Like any other heart failure, CTs dog can also be managed with beneficial effects using diuretics and angiotensin converting enzyme inhibitors (Gordon et al., 1982; Macdonald, 2006; Gustavo et al., 2012). Diuretics is the primary drug in the management of heart failure, as it reduces preload and relieves congestion secondarily to cardiac dysfunction. However, diuretics should never be used as single therapy as they activate Rennin Angiotensin Aldosterone System (RAAS), therefore they should be used in conjunction with ACE inhibitors (Sandra, 2020). BENCH Study Group (1999) reported the effect of a long acting ACEi and benazepril on the survival times and clinical signs of dogs with heart failure and documented that the drug counteracts the adverse effects caused by ACE activity in heart failure. In the present study, the combination therapy significantly improved the clinical signs such as, breathing, physical activity and exercise strength and duration subsequently resulting in prolonged survival time.

From the available reports and present study, it may be concluded that the rare congenital cardiac anomaly,CTs should also be included in the differential diagnosis of heart failure particularly if presented at early life. Early detection not only helps to increase survival time of the affected dog, but also prevents unnecessary breeding.

The authors are thankful for the administration, PVNR TVU, Hyderabad in providing the facilities for completing the work.

The authors have declared no conflict of interest.