Background Information:

A two-year-old male beagle was presented to clinicians due to a fainting episode, coughing, and panting. He has had no previous health issues and is up-to-date on vaccinations and preventatives. 

Problem List: 

After performing a physical exam and several diagnostic tests, three major problems have been identified in order of concern. Several other problems that are not listed below but are still of concern were the high respiratory rate, septal wall thinning, and enlargement of pulmonary artery.

1. Right ventricular hypertrophy 

Right ventricular hypertrophy is the most concerning problem for the patient due to the degree of hypertrophy and its effect on other areas of the heart. Cardiac ultrasound revealed significant right ventricular hypertrophy. This is consistent with the patient's radiographs which showed right ventricular enlargement. Right ventricular hypertrophy is a thickening of the right ventral wall of the myocardium. Laplace’s Law states that wall tension is inversely proportional to the radius; thus, decreasing the radius of the ventricle by hypertrophy can alleviate ventricular wall tension (Figure 1). If the body cannot alleviate wall tension, this can lead to diminished cardiac output, which puts the patient at risk for heart failure.^[1] Significant hypertrophy is indicative of a compromised circuit in which the right ventricle must work harder to pump blood through pulmonary circulation to maintain cardiac output.^[2] It is also concerning because it may be directly responsible for the thin interventricular septum and reduced systolic and diastolic dimensions of the left ventricle.  Right ventricular hypertrophy is a major symptom of many concerning heart defects such as pulmonic stenosis, patent ductus arteriosus, and blood shunting - all of which can lead to heart failure if left untreated. 

2. Turbulence through pulmonic valve presented by a grade V/VI heart murmur

Pulmonic turbulence was initially detected as a grade V/VI murmur upon auscultation during the physical exam. Cardiac ultrasound data unveiled this murmur to be turbulence through the pulmonic valve. The continuous wave Doppler velocity is extremely elevated through the pulmonic valve with a velocity of 5.73m/s = 131.39mmHg; Normal value is 30mmHg or less.^[3] Severe pulmonic turbulence could be caused by pulmonic stenosis or some obstruction in the pathway to pulmonary circulation. This is concerning because pulmonic stenosis leads to inefficiency in oxygenation of blood due to compromise blood flow, which may starve tissues in the body and cause cyanosis, fainting, and possibly death.^[3]

3. Fainting episode of patient 

The episode of fainting that happened to Hank is concerning. Although this information is not as specific in diagnosing what type of cardiovascular problem the patient has, it illustrates the progressive stage of disease. Though most of the diagnostic data points to a cardiovascular problem, this fainting spell may have been a seizure which is indicative of a neurological problem. In terms of a cardiovascular problem, syncope is a physical symptom in which the heart cannot efficiently pump blood to the brain.^[4] This is a major problem because the patient's disease has progressed to a severity that compromises brain function. 

Differentials: 

1. Valvular Pulmonic Stenosis

Pulmonic stenosis is the narrowing of the passage from the right ventricle to the pulmonary artery due to thickening of the surrounding myocardial tissue or a defect in the pulmonic valve which is specifically called valvular pulmonic stenosis (Figure 2). This congenital heart defect causes obstruction of blood flow to the pulmonary artery resulting in pulmonary hypertension and venous backflow. Classic symptoms of pulmonic stenosis are increased respiratory rate, increased heart rate, heart murmurs, and fainting which are all consistent with our patient.^[3] Fainting can occur due to insufficient blood supply to the brain which is caused by obstruction of pulmonary circulation. The obstruction of the pulmonary artery decreases the amount of blood flow that can undergo gas exchange, thus causing a deficiency in oxygen in the blood.^[4] Breed disposition is also consistent with pulmonic stenosis because beagles are genetically pre-dispositioned to vavular dysplasia which can lead to pulmonic stenosis.^[5]

a. Echocardiography

Cardiac ultrasound allowed us to diagnose the patient with severe right ventricular hypertrophy and pulmonic valve elongation and doming. Doppler data found turbulent blood flow through the pulmonic valve. Both findings strongly support pulmonic stenosis because ventricular hypertrophy can occur secondary to pulmonic stenosis.^[6] The health of the valves appears to be compromised and are obstructing flow through the valve. Doming of the valves signifies valvular pulmonic stenosis. Continuous wave Doppler also indicates an elevated velocity of flow through the pulmonic valve which is consistent with pulmonic stenosis. ^[6]

b. Radiography

Although radiographs cannot diagnose pulmonic stenosis, but they are consistent with symptoms of the pulmonic stenosis. Right heart enlargement, right ventricular enlargement and pulmonary artery dilation, are indicated in both the VD and Lateral views. This is consistent with right ventricular hypertrophy and valvular stenosis. The rounded shape of the heart in the VD view is also consisted with pulmonic stenosis. ^[7] Another differential for right heart enlargement is patent ductus arteriosus, a condition that occurs when a fetal shunt is retained after birth. The shunt connects the pulmonary artery to the aorta – this causes inefficient blood flow due to aortic blood flow leaking back into pulmonic circulation. Right ventricular hypertrophy occurs as compensation for systemic hypoperfusion.^[8] 

c. Electrocardiography

Lead II negative QRS waves and rS amplitudes are consistent with right ventricular hypertrophy because myocardial thickening causes a displacement of depolarization to the right side of the heart. This direction is opposite of lead II’s positive probe due to depolarization towards the hypertrophic tissue (Figure 6). This causes a negative wave on the ECG and thus causing a right axis shift in the ECG (Figure 5). ^[9] In a normal patient, you would expect a normal, positive QRS wave due to depolarization in the direction of lead II’s positive probe (Figure 7).

2. Reverse Patent Ductus Arteriosus 

A patent ductus arteriosus is a congenital heart condition where the ductus arteriosus, a fetal shunt, is retained after birth. Patent ductus arteriosus is likely caused by a retention of the sixth aortic arch during fetal development. During fetal development, fetal circulation does not require pulmonary circulation due to all of gas exchange occurring in the mother’s placenta. A shunt from the pulmonary artery to the aorta bypasses the non-functioning lungs. At birth, this shunt should close and becomes the ligamentum arteriosus.^[10] If the shunt is retained, it is called a patent ductus arteriosus. Though mild to moderate cases of PDA tend to have left ventricular hypertrophy, large PDA cases have right ventricular hypertrophy. Thus, the shunt pathway is reversed from right to left due to high pulmonary hypertension causing reverse PDA.^[11][12] PDA is consistent with many symptoms of our patient including high respiratory rate, heart murmurs, and fainting. Fainting, or syncope, can occur due to the shunting of deoxygenated blood to systemic circulation. An insufficient amount of oxygenated blood is pumped to the brain which causes fainting. Fainting is especially prevalent in in affected patients during exercise because the heart cannot compensate and achieve the necessary cardio output which will cause brain blood supply to wane. In a case study of reverse PDA in a dog, the patient had similar fainting episodes. Further progression of this condition can lead to worse episodes of fainting and even seizures. It is highly likely that Hank may have experienced a small seizure during his fainting episode.^[13]   

a. Heart Auscultation

The grade V/VI left basilar systolic heart murmur is consistent with reverse PDA and not as consistent with pulmonic stenosis. A heart murmur indicates turbulent blood flow as opposed to laminar flow which does not produce a murmur. A grade V/VI systolic murmur is presented when a patient has a large disturbance in blood flow during ventricular systole. A left-sided basilar murmur would be auscultated due to shunting of blood and turbulence from the pulmonary artery to the aorta which is can be heard at the left heart base. Thus, this loud murmur is most likely due to the shunting of blood from the pulmonary artery to the aorta which is greatest during systolic contraction. Another differential for this type of murmur is sub-aortic stenosis which is valvular stenosis of the aortic valve due to obstruction or valve disease.^[14]

b. Radiographs

Radiographic findings are consistent with right ventricular hypertrophy as shown in the right heart enlargement. See Figures 2 and 3 for further information.

c. Echocardiography

Cardiac ultrasound diagnosed septal flattening, right ventricular hypertrophy, small left ventricle, and high-velocity pulmonary regurgitation which are all secondary to PDA.^[11] However actually diagnosis of PDA was not indicated in the interpretation which contradicts this differential. Another echocardiograph and further testing such as an MRI and bubble test should be performed to reassess data.^[12] A bubble test is a contrast test that involves injecting a heart chamber with saline in order to determine the direction of flow. The saline solution appears as cloudy bubbles in an echocardiogram and can positively determine PDA.^[12] 

d. ECG

ECG results are consistent with right ventricular hypertrophy which is consistent with large PDA. See Figures 4 and 5 for more information.

Understanding: Pathophysiological Changes

There are many pathophysiological changes in Hank’s cardiovascular circulation that are detrimental to his health. Treating his pulmonary hypertension should be a priority as leaving this condition untreated could potentially cause heart failure. Heart failure is the inability of the heart to keep up with the body’s demands. Heart failure most readily diagnosed when there is a cardiac enlargement with high vertebral heart score (VHS > 10.7), evidence of venous congestion, and pulmonary edema.  In a reverse PDA case study, the clinician prescribed Sildenafil and suggested that congestive heart failure drugs such as Vetmedin, ACEIs, or Furosemide may need to be added to regime dependent upon the patient’s blood chemistry and values. With Sildenafil, the owner noticed improvement in two week after starting treatment^[12]

The high respiratory rate and history of fainting is worrisome, so a CBC and blood-gas values should be tested to determine VQ internals and cardiac efficiency. Because both differentials cause insufficient gas exchange of oxygen, I would expect to see lower pO2 levels for both conditions. Therefore, exercise must be restricted and respiration should be monitored by the owner.

In the case of possible pulmonic stenosis, balloon vavuloplasty or surgical repair are the only treatment options that can permanently reserve the disease, but patients must be an optimal candidate for these procedures. I believe that Hank is a good candidate for surgery because of his young age, but bloodwork must also be done to determine this. If the patient cannot undergo surgery, atenolol or other beta blockers can be given to guard against arrhythmias and fibrillation.^[5]

For treatment of PDA, surgical ligation of the shunt can be performed. If the patient is not a good candidate for heart surgery, or medical management of polycythemia in reverse PDA patient must be implemented.^[11]  Phlebotomy or administration of hydroxyurea or methotrexate can help alleviate this condition.^[12]

Conclusions/Self-Reflections

This assignment was challenging, yet less cumbersome than the first Scholar assignment due to already having knowledge of cardiovascular anatomy and physiology and having a species of patient with more scientific literature available. My first problem was deciphering auscultations and how they relate to specific cardiopathologies. I have limited experience with auscultation, besides counting heart rate and understanding the basics of turbulence. I had to watch several videos online and research material that helped me understand what a grade V/VI left basilar heart murmur was and why the pathophysiology of certain heart conditions could cause this. My second problem was allowing myself to see information beyond one differential. In this case, almost all data pointed towards pulmonic stenosis, and it was difficult to make myself interpret the data without this bias in making a second differential. However, after several hours of relooking at the material and writing down small discrepancies between my first differential and the diagnostic data, I was able to make a second differential. I need to learn to view data without have a biased view and a limited scope, as a seemingly simple case may actually have a completely different diagnosis. Although I initially thought pulmonic stenosis was the definite culprit in this case analysis, I began to more strongly support my second differential of Reverse PDA. 

Footnotes

1. ^ Lorell, B. H., and Carabello, B. (2000): Left Ventricular Hypertrophy. Clinical Cardiology: New Frontiers. 102:470-479 http://circ.ahajournals.org/content/102/4/470
2. ^ Voelkel, N. et al (2006): Right Ventricular Function and Failure: Report of a National Heart, Lung, and Blood Institute Working Group on Cellular and Molecular Mechanisms of Right Heart Failure. Circulation. 114:1883-1891. http://circ.ahajournals.org.proxy2.library.illinois.edu/content/114/17/1883
3. a, b, c NNadas, Alexander S., and Robert Curtis Ellison. (1977). Pulmonary Stenosis. Nadas, A. Pulmonary stenosis, aortic stenosis, ventricular septal defect: clinical course and indirect assessment: report from the joint study on the natural history of congenital heart defects. 87.
4. a, b Tidholm, A. (1997) Retrospective study of congenital heart defects in 151 dogs. Journal of Small Animal Practice. 38: 94-98. http://onlinelibrary.wiley.com.proxy2.library.illinois.edu/doi/10.1111/j.1748-5827.1997.tb03326.x/full
5. a, b Francis, A.J. et al. (2011) Outcome in 55 dogs with pulmonic stenosis that did not undergo balloon valvuloplasty or surgery. Journal of Small Animal Practice. 52: 282-288. http://onlinelibrary.wiley.com.proxy2.library.illinois.edu/doi/10.1111/j.1748-5827.2011.01059.x/full
6. a, b Lima, C. Oliveira et al. (1983) Noninvasive prediction of transvalvular pressure gradient in patients with pulmonary stenosis by quantitative two-dimensional echocardiographic Doppler studies. Circulation. 67: 866-871. https://www.researchgate.net/publication/16374261_Noninvasive_prediction_of_transvalvular_pressure_gradient_in_patients_with_pulmonary_stenosis_by_quantitative_two-dimensional_echocardiographic_Doppler_studies
7. ^ Fries, R. “Imaging: Cardiac Pathophysiology.” 6 February 2006, University of Illinois School of Veterinary Medicine, Urbana, IL. Lecture. 
8. ^ Dice, J. E., et. al. (2007): Patent Ductus Arteriosus: An Overview. Journal of Pediatric Pharmacology and Therapeutics. 12: 138-146. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3462096/
9. ^ Gertsch, M. (2009) Right Ventricular Hypertrophy. The ECG Manual: An Evidence-Based Approach. 59-66.
10. ^ Schneider, D. and John Moore (2006) Patent Ductus Arteriosus. Circulation. 114:1873-1882. https://doi.org/10.1161/CIRCULATIONAHA.105.592063
11. a, b, c Houghton, H. and Wendy Ware (1996) Patent Ductus Arteriosus. Iowa State University Veterinarian. 58: 83-87. http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3565&context=iowastate_veterinarian
12. a, b, c, d, e Scurtu, I. et al. (2016) Reverse PDA – Less Common Type Of Patent Ductus Arteriosus - Case Report. Bulletin UASVM Veterinary Medicine. 73: 351-355. http://dx.doi.org/10.15835/buasvmcn-vm:12225
13. ^ Ackerman, N. (1992) A RIGHT-TO-LEFT SHUNTING PATENT DUCTUS ARTERIOSUS WITH SECONDARY PULMONARY HYPERTENSION IN A DOG. 33:141-144. http://dx.doi.org/10.1111/j.1740-8261.1992.tb01434.x
14. ^ DeFrancesco, T., Cardiac Auscultation, https://cvm.ncsu.edu/wp-content/uploads/2015/06/DeFrancesco2012_CardiacAusculation.pdf