Signalment and History

Hank is a 2 year old castrated male Beagle. He weighs 12 kg and has a normal BCS at 5/9. The owner stated that Hank was let into the backyard and tried to chase a squirrel before he began panting and then fell over onto his side. He appeared dazed and limp and had urinated during the episode. Hank recovered very quickly, he sat up and appeared groggy after about five seconds and then was completely normal after about a minute. 

Presenting Complaint

Hank has presented to the UIUC veterinary teaching hospital for the fainting episode that occurred two weeks ago. His owners took him to a primary care veterinarian following the episode and the RDVM diagnosed him with V/VI loud heart murmur and sent him to the teaching hospital for further assessment. The owner has since kept Hank's activity level low and he has not had another episode since. He has no other known health issues, though his previous primary care veterinarian did note that he had always had a heart murmur. He is up to date on vaccinations and is not on any medications beyond flea, tick, and heartworm preventatives.

Physical Exam Findings

Hank is BAR (bright, alert, responsive), happy, and playful in the examination room. His temperature is 102.7ºF, his pulse is 135 beats/min, and an accurate respiratory rate could not be taken as he was panting, all of which are normal. EENT (eyes, ears, nose, throat) all within normal limits with some mild ceruminous debris in the external ear canals. Lymph nodes, lungs, abdomen, urogential, neurological, and skin assessments all within normal limits as well. A V/VI left basilar systolic heart murmur with strong and synchronous pulses was auscultated. A blood pressure was also taken in right lateral recumbancy via the doppler method and was within normal limits(145 mmHg systolic). 

Diagnostics

An ECG was performed to further assess heart function following auscultation of the heart murmur and it was found that he has an underlying sinus arrhythmia with a deep S-wave in lead II and a right axis shift, indicative of right ventricular enlargement.

Hank's ECG results.

In addition, thoracic radiographs were performed, a right lateral and a VD with no previous radiographs for comparison. His cardiac silhouette is within normal limits (<10.6), but there is a bulge at the 1 to 2 o'clock position in VD and at the base in right lateral. The right ventricle appears enlarged in VD and there is sternal contact in right lateral. The pulmonary veins and arteries appear normal along with everything else in the thoracic cavity. The main pulmonary artery, however, appears dilated. These results are indicative of main pulmonary artery enlargement and confirms the right ventricular enlargement from the ECG.

VD view

Right lateral recumbancy

 Finally, to further determine the etiology of Hank's heart issues, echocardiography was performed in 2D, M-mode, and volumetric assessment functions. The right ventricle is severely concentrically hypertrophied with normal systolic function. The pulmonic valve leaflets are elongated and tethered and show doming during ventricular systole. There is turbulent blood flow present through the pulmonic valve based on color Doppler. Continuous wave Doppler through the pulmonic valve is severely elevated (131.39mmHg [Normal < 30mmHg]). The right atrium appears normal in size. The left ventricular internal dimensions are severely reduced in diastole and systole and the interventricular septum is flattened, likely from markedly elevated right ventricular pressure. The left ventricular systolic function is normal and the left atrium is normal in size. The transaortic velocities are normal. There is no evidence of pericardial effusion or cardiac masses.

Echocardiography showing concentric hypertrophy of the right ventricle and elongation, tethering, and doming of the pulmonic valve leaflets.

Problem List

The three most important problems in this case in order from least to most concern are the grade V/VI basilar systolic heart murmur, the right ventricular hypertrophy, and the elongated and tethered pulmonic valve leaflets. A grade V/VI heart murmur is defined as a loud murmur with a palpable thrill and a basilar systolic murmur indicates that it is most audible in the heart base during systole, or ejection of blood (Kittleson, "Diagnosis of Heart Disease"). The right ventricle is concentrically hypertrophied based on the echocardiography findings, so the wall has enlarged with the chamber remaining normally sized, suggesting that something is causing the heart to need a greater contractile force to move blood into the pulmonary circulation (Murray et al, 1979). The right ventricular hypertrophy and the basilar systolic heart murmur are both indicative of the right heart having to work harder to pump blood into the lungs for some reason. The elongated and tethered pulmonic valve leaflets are likely the reason that that the right heart is having to work so hard. The valve cannot open properly because they are so long and so this results in a doming effect, severely reducing blood flow and requiring the right ventricle to produce much more pressure than it normally would to force blood through the domed valve, as shown in the below angiogram (Laste, "Congenital Heart Disease in Companion Animals"). 

https://www.mspca.org/angell_services/congenital-heart-disease-in-companion-animals/

Differential Diagnoses

The two most likely differentials given Hank's symptoms and the diagnostic results are valvular pulmonic stenosis or pulmonary hypertension. Valvular pulmonic stenosis results in obstruction to right ventricular outflow due to, in this case, dysplasia of the pulmonic semilunar valves (Tou, "Pulmonic Stenosis"). Based on the echocardiography, Hank's pulmonic valve leaflets are elongated and tethered and so they cannot part enough to allow blood flow through normally, resulting in a doming effect that obstructs blood flow. Beagles are one of the breeds with a predisposition for valvular pulmonic stenosis, so this differential is well supported based on the case evidence (Tou, "Pulmonic Stenosis"). The right ventricle must generate increased pressure during systole to overcome the stenosis, which typically leads to right ventricular concentric hypertrophy and dilation. In addition, as the right ventricle hypertrophies, ventricular compliance diminishes, leading to increased right atrial pressure and venous congestion. The turbulent jet of blood flow across the stenosis deforms the wall of the main pulmonary artery, resulting in a poststenotic dilation (Tou, "Pulmonic Stenosis"). This is because pulmonary artery pressures are normal, so blood goes from moving very quickly due to the increased right ventricular pressures to very slowly almost immediately, causing the dilation of the pulmonary artery seen in the thoracic radiographs. Affected dogs typically have issues with exercise intolerance, as in Hank's fainting episdoe. Right-side CHF may be present and is characterized by ascites or peripheral edema, but our diagnostics do not indicate that this is currently an issue in Hank's case, as his VHS is normal (<10.6) and his radiographs and echocardiography do not show any edema or effusion. A systolic murmur is typically present and best heard at the left heart base (over the pulmonary valve) with a palpable thrill, as in Hank's case. Electrocardiography will demonstrate evidence of right ventricular enlargement (deep S waves in lead II), just as Hank's does. Radiographic abnormalities include right ventricular enlargement, dilation of the main pulmonary artery, and diminished pulmonary perfusion. Echocardiography is needed to obtain a definitive etiology and may demonstrate right ventricular hypertrophy, thickened and doming pulmonic valve cusps, and turbulent blood flow across the stenosis (Tou, "Pulmonic Stenosis"). Hank's diagnostic findings and his breed predispositions fit this differential almost exactly, but there is another clinical finding in this case that brings up a second important differential, pulmonary hypertension.

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A second, related differential based on the diagnostic findings is pulmonary hypertension. Pulmonary hypertension is defined as any elevation above normal pressure in the pulmonary artery, as this vessel is very noncompliant and does not handle high pressures well (Williams, "Canine Pulmonary Hypertension Part 1"). Hank's pulmonary arterial pressure is 131.39 mmHg based on continuous wave Doppler, significantly higher than the normal 30 mmHg, making pulmonary hypertension an extremely important differential in Hank's case. 

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Pulmonary hypertension is most common in small breed, middle-aged dogs, so at 2 Hank is younger than the commonly afflicted dog (Williams, "Canine Pulmonary Hypertension Part 2"). One of the most typical symptoms associated with pulmonary hypertension is exercise intolerance, which is why Hank initially presented to the RDVM (his fainting episode). In addition, a heart murmur is a also common physical exam finding in patients with pulmonary hypertension, and so despite his young age this differential is high on our list of concerns (Williams, "Canine Pulmonary Hypertension Part 2"). It is important to determine the cause of the pulmonary hypertension in order to treat the animal. As the above figure indicates, pulmonary hypertension can have a wide variety of underlying causes and, based on the doming pulmonary valve leaflets and right ventricular hypertrophy, it is safe to say that pulmonic stenosis is the likely cause of the pulmonary hypertension in Hank's case. 

Understanding 

These are not Hank's radiographs, but they show the relative location of the pulmonary artery in lateral and VD views.

The above image shows the relative location of the main pulmonary artery on lateral and VD thoracic radiographs of the dog, as it is harder to see on Hank's radiographs (below). 

Hank's lateral thoracic radiograph.

Hank's radiograph shows significant sternal contact of the right ventricle, which is why we concluded that there was hypertrophy, and we can also see bulging of the main pulmonary artery if we look in the same area shown in the top figure. The three most likely differentials for right ventricular hypertrophy and main pulmonary artery dilation occurring together are pulmonic stenosis and pulmonary hypertension, as previously stated (Tou, "Pulmonic Stenosis" and Williams, "Canine Pulmonary Hypertension Parts 1 and 2'), and tricuspid valve dysplasia (Tou, "Tricuspid Valve Dysplasia"). Both of these issues create the need for higher than normal pressure in the right ventricle to move blood into the pulmonary circulation. In pulmonic stenosis, the blood will be at a high pressure and speed before the obstructed pulmonic valve and then immediately slow down once it passes it, causing dilation of the pulmonary artery (Tou, "Pulmonic Stenosis"). In tricuspid valve dysplasia, as indicated in the below figure, regurgitation occurs back into the right atrium, causing volume overload and pulmonary artery dilation (Tou, "Tricuspid Valve Dysplasia"). 

https://www.merckvetmanual.com/circulatory-system/congenital-and-inherited-anomalies-of-the-cardiovascular-system/tricuspid-valve-dysplasia

 Heart murmurs are audible vibrations caused by either turbulent blood flow or by movement of cardiac structures such as the valves or the chordae tendinae (Kittleson, "Diagnosis of Heart Disease"). A V/VI basilar systolic heart murmur means that Hank has a loud murmur with palpable thrills in the basal region of his heart that can be heard only during systole, or ejection of blood. Hank has a heart murmur because of turbulent blood flow across his pulmonic stenosis. The doming pulmonic valves create abnormally high pressure in the right ventricle, which results in high flow speeds and turbulence (Kittleson, "Diagnosis of Heart Disease"). The most likely differentials for Hank's murmur are, once again, pulmonic stenosis, pulmonary hypertension, and tricuspid valve dysplasia causing regurgitation back into the right atrium. All of these differentials involve increased ventricular pressures, flow speed, and thus turbulent blood flow.

Hank's fainting episode was likely caused by a brief lack of oxygen to his brain. The pulmonic stenosis lead to pulmonary hypertension, which caused imparied oxygen transport, reduced cardiac output, and systemic hypotension resulting from systemic vasodilation and underfilling of the ventricles (Williams, "Canine Pulmonary Hypertension Part 2"). Hank's systolic blood pressure was normal at 145 mmHg, but this may be due to heightened stress from being at the veterinary hospital and being restrained in lateral recumbancy.

This fainting episode can be best understood via two basic science principles: Ohm's Law and ischemic hypoxia. Ohm's law states that flow is equal to pressure difference divided by the resistance of the system. In the heart, the pressure difference is between the right ventricle and the left atrium. In a normal heart, this would be 25mmHg - 10mmHg with a resistance of 5, resulting in a flow of 3 L/min. In Hank's case, the pressure difference between the right ventricle and the left atrium has to increase in order to maintain normal flow because the stenosis has increased the resistence of the system. The stenosis and the resulting right ventricular hypertrophy caused an inability to produce a normal stroke volume, reducing overall cardiac output. The decreased cardiac output leads to lower perfusion of the tissues, the ischemic hypoxia, and decreased oxygen delivery to the tissues, causing him to faint during strenuous exercise. 

The pathophysiological changes that should be reversed with therapy are the pulmonary hypertension and the doming pulmonic valves. The pulmonary hypertension can be treated with oxygen supplementation or anti-inflammatory or bronchodilating agents to treat the underlying pulmonic disease (Williams, "Canine Pulmonary Hypertension Part 2"). Oxygen supplementation following future fainting episodes will be an effective short-term, emergency treatment to improve systemic oxygen delivery to tissues. The anti-inflammatory and bronchodilating agents will help reduce the pressure in the pulmonary artery created by the stenosis. The doming pulmonic valves can be treated with balloon valvuloplasty or surgical intervention such as valvulotomy, patch grafting, partial valvulectomy, or conduits (Mcmahon and Saelinger). This will remove the cause of the pulmonic stenosis and will thus also treat the pulmonary hypertension and so is the option that is likely to provide the best long term prognosis for Hank.

I felt much more confident this second time around working out this case, the only thing I feel guilty about is using the possible differentials that were given to us in the interpretation of the thoracic radiographs and echocardiography that we were given. Based on what we learned in imaging and physiology before the midterm, however, these differentials were the most likely that I could find in any source, especially since it is clear to me that the two of them are closely related to each other. While I wish that I had gotten a case about something other than heart disease since that is what we had last time, I think that this has been excellent practice at interpreting thoracic imaging techniques and using the skills taught to us by Dr. Fries. However, I did have some difficulty with deciding on which problems were most important this time around, and I still feel like I should have included the increased pulmonary artery pressure instead of the basilar heart murmur, so I might change that in my next revision. But, this could also just me continuing to worry about finding the exact right answer and that will probably never change.