Signalment and History
Hank is a two year old neutered male beagle who was referred to the University of Illinois Cardiology Service for fainting. Two weeks ago, Hank was out for his bathroom break when he began to chase a squirrel. In the middle of his chase, he started to pant, appeared weak, and then fell sideways. When the owner approached Hank, he seemed to be dazed and had urinated. However, within one minute Hank recovered and was back to normal.
Hank's family recently moved to the Urbana-Champaign area. They took Hank to a new veterinarian after he fainted, and during his examination, the veterinarian heard a grade V/V loud heart murmur. Hank was then referred to the U of I's Cardiology Service
After scheduling Hank's cardiology appointment, Hank's exercise was restricted and he has not had any more fainting episodes. Prior to this, Hank had always been a healthy dog and is currently up to date with vaccines, flea, tick and heartworm prevention. His previous veterinarian has no record of a heart murmur.
His presenting complaint is coughing and panting
Physical Examination
Physical Examination
On the physical exam, Hank was within normal limits for temperature and pulse. He was panting while trying to get a respiration rate. Eyes, Ears, Oral cavity, teeth, lymph nodes, respiratory system, abdomen, urogenital, neurological and skin and hydration were all unremarkable. The cardiologist did hear a grade V/VI left basilar systolic heart murmur with strong synchronous pulses, but no arrhythmias were noted. Further diagnostics were done and will be explained later in this case study.
Problem List
Problem List
1) The most important problem is the pulmonic valve leaflets are tethered and elongated. The pulmonic valve allows for blood to flow from the right ventricle through the pulmonary artery and into the lungs. In a healthy heart, the pulmonic valve is a one-way valve which prevents the blackflow of blood into the right ventricle. It is a semilunar valve that is composed of 3 leaflets (1). As seen in the image below, in a normal heart, the Pulmonary valve leaflets open to let deoxygenated blood flow through to become oxygenated in the lungs.
When the pulmonic valve leaflets become elongated and tethered, they can cause a number of problems in the patient. The tethering of the pulmonary valve leaflets can cause narrowing of the pulmonary valve which will prevent it from opening normally (2). As seen in the image below, the leaflets are tethered and creating an obstruction for blood flow to come in from the right ventricle. This obstruction can lead to turbulent flow through the pulmonic artery and make the heart work harder to pump the blood through (3). This is what is occuring within Hank's heart and this obstruction can lead to exercise intolerance, and if severe enough, can turn into right-sided congestive heart failure (3).
2) The second most important problem is the right ventricular hypertrophy. The right ventricle's main function is to pump deoxygenated blood into the lungs. The difference in pressures allows for blood to move through the right ventricle and through the pulmonic valve (4). Normally, the right ventricle has a thinner wall than the left ventricle. If there happens to be a pressure overload, like in the case of Hank, the right ventricle becomes hypertrophied due to the increase in workload.
3) The V/VI left basilar systolic heart murmur is the third most important problem. A grade V/VI murmur is loud and audible with the stethoscope barely touching the chest. It can also be felt through the chest wall. Heart murmurs are made from a disturbance in blood flow (6). One type of disturbance is turbulent flow through normal or abnormal valves. Another type is an outflow obstruction or flow into a dilated great vessel. In this particular case, Hank was found to have turbulent flow through his pulmonic valve and his pulmonary artery is enlarged. When the heart murmur is cause by structural heart disease, associated symptoms include coughing, weakness, or exercise intolerance. Systolic heart murmurs are caused by numerous diseases, such as Pulmonic Stenosis and Tetralogy of Fallot. Heart murmurs are important to monitor because they can help determine the extent of disease (6). In Hank’s case, the heart murmur is loud and further diagnostics showed abnormalities within the heart.
Differentials
Differentials
1) Pulmonic Stenosis (PS). In pulmonic stenosis, there is an obstruction in the outflow of the right ventricle. In Hank’s case, there is elongation and tethering of the pulmonic valve leaflets that is causing an obstruction. There are different types of pulmonic stenosis, but valvular is the most common type found in dogs. Beagles are a breed that are more susceptible to developing this disease and it is common to find in young dogs (7). The pathophysiology of PS involves the hypertrophy of the right ventricle. During systole, to overcome the tethering of the leaflets in the pulmonary valve, the right ventricle must generate a lot of pressure, which causes hypertrophy over time(3). This was seen in Hank’s radiograph and echocardiograph. The increase in pressure, leads to turbulent flow across the pulmonary valve and cause a dilation of the pulmonary artery. This was also see in Hank’s radiograph as the bulge on the 1-2 o’clock position. According to Merck Veterinary manual, a systolic heart murmur is evident and is easily identified at the left base of the heart. This description matches Hank’s heart murmur found by the cardiologist (3). Hank’s fainting is most likely due to an reversed flow of electrical current. In the EGC, the QRS complex is inverted which suggests an abnormal flow of current. Since the heart cannot pump normally due to the abnormal current, an increase in heart rate would cause fainting. The heart woud not be able to keep up with the demands from the body and the decrease supply of blood to the brain would cause a fainting spell (12).
2) Pulmonary Hypertension (PH) In PH, there is an increase in blood pressure within the arteries of the lungs. A high arterial pressure decreases blood flow to the lungs and the right ventricle must work harder to pump blood into the lungs. This increase in workload causes hypertrophy in the right ventricle and will cause a dilation in the pulmonary artery (8). There is less oxygenated blood that flows to the body from the heart and lungs. In the physical exam and history of a patient with PH, they may be exercise intolerant, have episodes of fainting, and have a heart murmur. PH is caused by underlying diseases, however, in most cases, the disease is never diagnosed. The thoracic radiographs and echocardiograph will show an enlarged pulmonic artery, and enlarged right ventricle (9). All of these can be seen in Hank’s case.
Evidence from case observations
Evidence From Case Observations
Upon physical exam, a V/VI left basilar systolic murmur was heard. These murmurs are prevalent in pulmonic stenosis because the pulmonic valve can be seen in the left base region of the heart. Heart murmurs are also present in pulmonary hypertension. In both diseases, the blood supply is typically limited due to the right ventricle hypotrophy and either the stenosis or the increased pulmonary artery pressure (9,3). The right hypertrophy can be seen in the ECG with the presence of deep S waves in lead II (shown below).
The thoracic radiographs show an enlargement of the right ventricle due to the increased sternal contact seen on the lateral image. A bulge at the 1 to 2 o’clock position is thought to be an enlargement of the main pulmonary artery. The echocardiography showed severe hypertrophy of the right ventricle and elongated and tethered pulmonic leaflets. They were seen forming a dome during systole and a turbulent flow was noted as well. All of these irregularities are seen within pulmonic stenosis (3). The turbulent flow causes the pulmonary artery to change and become dilated since there is a high velocity of flow running through it and most likely hitting the walls. Although in pulmonic hypertension, pulmonary valve tethering is not listed as a problem, it can contribute to pulmonary hypertension.
Understanding
Understanding
a) Identify the main pulmonary artery on the radiographs. List at least 2 differentials for the buldge in the cardiac silhouette/main pulmonary artery dialation.
Two differentials for the main pulmonary artery dilation: Pulmonary hypertension and Pulmonary Stenosis. In Pulmonary stenosis, the disfunction of the pulmonary valve causes high pressure in the right ventricle and a turbulent flow of blood shoots through the pulmonic valve and into the main pulmonic artery. After some time, the main pulmonic artery will become distended due to the turbulent flow (3). In Pulmonary hypertension, there is high pulmonary arterial pressure. This leads to hypertrophy of the right ventricle. Due to the high arterial pressure an enlargement of the pulmonary artery is usually seen in the exact position Hank's was found in: the 1-2 o'clock position (9). Both of these diseases have turbulent flow that cause the blood to shoot up the main pulmonary artery and alter the structure of the artery.
b) Why does Hank have a heart murmur? Describe what a V/VI systolic murmur is.
Hank’s heart murmur consists of turbulent flow from the right ventricle into the pulmonary artery. This causes vibrations because of the fast speed and the blood is hitting the walls of the main pulmonic artery. A grade V/VI systolic murmur is heard during systole and is very loud and has a thrill (6).
c) What are the differentials for a V/VI left basilar systolic heart murmur
The differentials for a V/VI left basal systolic murmur are the concentric hypertrophy of the right ventricle and the tethered leaflets of the pulmonic valve. The pulmonic valve is located in the left base of the heart and when the leaflets are tethered, the right ventricle must work harder to overcome the teathered leaflets. The combination of these two cause turbulent flow and as a result, a left basilar systolic heart murmur. The V/VI grade means that there is loud turbulent flow through the pulmonic valve and main pulmonary artery.
d) What is the most likely cause for Hank's fainting episode?
Hank's ECG showed deep S-waves and a right axis shift which implied enlargement of the right ventricle. The ECG also showed an inverted QRS complex which suggested that the normal electrical conduction of the heart has been affected by the hypertrophy of the right ventricle. This disruption of the electrical flow causes the heart's systole and diastole periods to be disrupted. Due to the abnormal eletrical heart rhythm, and the increase in heart rate while chasing the squirrel, the patient exhibited a fainting episode (12).
e) Two science principles
1) Concentric hypertrophy: There are a number of ways the ventricles can hypertrophy but in concentric hypertrophy, there is an increase in ventricular wall thickness. This is due to an increase in systolic and diastolic blood pressure which causes a pressure overload and in turn, an increase in wall thickness. This can be seen in Hank's case. The walls of the right ventricle are becoming thicker due to the increase in workload from the pulmonary stenosis.
2) Turbulent flow vs. Laminar flow: Laminar flow is the type of blood flow that is typically seen in arteries. It is at a constant speed and travels in a parabola form. Turbulent flow is irregular movement of blood with rapid currents. This flow can be caused by stenosis and is the cause for most heart murmurs. In Hank's case, there was tubulent flow found flowing through the pulmonic valve which is most likely the reason for Hank's grade V/VI left basilar heart murmur.
f) In general terms, if you could reverse some of the pathophysiological changes in Hank with some therapy, what changes would you want to reverse?
To reverse the pathophysiological changes, I would first recommenf reversing the right ventricular hypertrophy and the pulmonic valve tethering. Hank would have to undergo balloon valvuloplasty or surgery to correct the valvular stenosis and this would overtime reduce the right ventricular hypertrophy since it will have a reduced workload (7). If the owners are unable to afford this procedure, I would try to medically manage Hank with a beta-blocker like atenolol. This medication helps to decrease the heart rate and allow for a longer diastole period(10). It can help to relax the muscles and dialate the stenosis within the pulmonary valve (12). However, without surgical intervention, the atenolol alone may not be sufficient to reduce Hank's symptoms.
Conclusions and Reflections
1) I had a difficult time throughout my research process. I could not find reliable primary references that helped explain a lot of the basic problems listed in this case. I had to rely on lecture notes as well as general websites. I did learn that veterinary sources like VIN and Merck Manual can be very helpful when trying to understand diseases.
2) I also had a difficult time writing. Writing has always been a weakness of mine, but working through these case studies has helped me to learn how to become a better scientific thinker, and in turn a better writer.
Resources
Resources
1) Unknown, Pulmonic/ pulmonary valve, IvyRose Holistic http://www.ivyroses.com/Define/Pulmonic_pulmonary_valve
2) Unknown, Pulmonary Valve Stenosis, Childrens Heart Specialists PSC
http://mykentuckyheart.com/information/PulmonaryValveStenosis.htm
3) Tou, Sandra P., Pulmonic Stenosis, Merck Manual
4) Unknown, How the heart works, Cardio Smart: American College of Cardiology
https://www.cardiosmart.org/heart-basics/how-the-heart-works
5) De Marco T, Mcglothlin D, Managing Right Ventricular Failure in PAH: An Algorithmic Approach. 2005.
http://www.phaonlineuniv.org/Journal/Article.cfm?ItemNumber=650
6) Unknown. Heart Murmurs in Dogs. PetMD.
http://www.petmd.com/dog/conditions/cardiovascular/c_dg_heart_murmur
7) 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 52.6 : 282
8) Peddle G, Pulmonary hypertension, Animal Emergency and Referral Associates
http://www.animalerc.com/pdf/cardiology/AERACardio_Client-Brochure_Pulmonary-Hypertension.pdf
9) Kittleson M, Pulmonary hypertension, Veterinary Information Network, 2012
http://www.vin.com/Members/Associate/Associate.plx?from=GetDzInfo&DiseaseId=583
10) Forney, B. Atenolol for Veterinary Use
11) Brook, W. Pulmonic Stenosis. 2008
http://www.vin.com/members/cms/project/defaultadv1.aspx?id=4952783&said=1