Cardiology Case Study: Cyanotic Heart Disease

History: Finley did not have the best start in life. She and a littermate were found in a dumpster and presented to The COVE by a good Samaritan shortly after we opened in 2012. Sadly, her sibling did not survive. Finley has, however, grown into four pounds of complete feistiness. Everyone at The COVE adores her cuteness and assertive personality. But let's just say that Finley has "her people" (of whom Danielle Russ, our Hospital Manager, is for some reason, not one....!).

Finley is a typical veterinary employee's pet. She has chronic intermittent GI upset and has experienced seizures. Microvascular dysplasia of her liver is suspected. Off and on, her mom, Tyler Bailey, now our surgery team lead, had reported episodes of lingual cyanosis when Finley was super-excited. A baseline echocardiogram was performed, and no overt abnormalities were noted.

Finley presented to our dentistry service on 8/22/2016 for removal of retained deciduous canine teeth and OHE. Finley's SPO2 never measured more than 92%. An echocardiogram was repeated postoperatively, and a positive contrast bubble study was performed. A patent foramen ovale with intermittent right-to-left shunting was diagnosed. Over the next few months, Finley's episodes of cyanosis worsened. Eisenmenger's physiology was suspected. Propanolol was prescribed and Finley's PCV has been carefully monitored for development of polycythemia. Finley continues to be the BAD-A** of The COVE, and she only becomes cyanotic when she is trying to assert her "authority."

Cyanotic Heart Disease in Veterinary Medicine

Typical blood flow occurs in series. Blood flows from the left heart (after receiving oxygen from the lungs) to the peripheral capillaries (where oxygen and nutrients are extracted), and then the deoxygenated blood travels to the right heart. It is then pumped into the pulmonary arteries back to the lungs to collect more oxygen, and never are the two circulations supposed to meet. The left heart must generate about 120/80 mmHg to propel blood into the entire body, and the right heart only has to generate about 25/15mmHg to send blood to the lungs.

Patients with cyanotic heart disease necessarily have two defects: a "hole/connection" between the two circulatory pathways and elevated pressure in the typically low-pressure right-side circulation. If enough right-to-left shunting occurs, a large amount of deoxygenated blood will enter the peripheral bloodstream. The kidneys recognize low oxygen levels and release erythropoietin to cause the bone marrow to make more red blood cells. Polycythemia often results. Patients can produce PCV as high as 75 percent! This is not a good scene.

The Most Common Causes of R-L Shunting

Tetrology of Fallot: This is a classic birth defect we are taught about in Veterinary/LVT school consisting of 1) ventricular septal defect, 2) overriding aorta, 3) pulmonic stenosis, and 4) right ventricular hypertrophy. The pulmonic stenosis must be severe enough to result in right heart pressure exceeding the left.

Atrial Septal Defect: There are four types of ASD. If the L-R shunting is severe, that could lead to a severe overload of blood flow to the pulmonary arteries due to the addition of the shunted circulation to normal circulation. The pulmonary arteries would have to remodel themselves to handle the increased blood flow. This could result in pulmonary hypertension - Eisenmenger's physiology. If the right-side pressures exceed the left, R-L shunting occurs.

Reverse PDA: In this case, the shunting occurs after the aortic arch, so normally oxygenated blood is delivered to the head, but the rest of the body receives the shunted blood. Differential cyanosis and episodes of rear limb weakness or collapse are hallmark signs of R-L PDA. There is typically no heart murmur. Click on the links to see video examples (WARNING: Viewer discretion is advised. Differential cyanosis video is of a dog's penis).

Treatment of Cyanotic Heart Disease

Open thoracic surgery or heart transplantation are the treatments of choice in humans. Obviously, this is not a valid option in most veterinary patients. Treatment is aimed at trying to maintain systemic pressure at a higher level than pulmonary pressure and controlling secondary polycythemia. Typically, propranolol is prescribed. This non-specific beta-blocker can increase systemic vascular tone and limit R-L shunting. If there is evidence of reactive pulmonary hypertension, sildenafil may be prescribed. If polycythemia occurs, it must be managed - therapeutic phlebotomy may be needed, but the goal would be to manage medically. Hydroxyurea, a bone marrow suppressant, can be titrated to maintain a PCV that is elevated but below a level that would cause blood sludging. Clopidogrel or other antithrombotics are often prescribed if PCV is chronically elevated.

Finley is doing well with her treatments and is tolerating two new human additions to her home. The members of Team COVE wince when they see her come to the office as a patient!

TECH TIP: Phlebotomy in the Polycythemic Patient - by Marie Moore, LVT

Polycythemia is an overproduction of red blood cells in the body. It is measured by monitoring the hematocrit, typically by measuring the percentage of pack cell volume (PCV). A normal hematocrit in canines is 35-55 percent and in felines is around 25-45 percent. A PCV above 55 percent in canines is considered polycythemic. Most patients become symptomatic at a PCV ~60-65 percent. These symptoms can include tachypnea, cyanosis, hyperemic mucous membranes, weakness, lethargy, and syncope (passing out). Other symptoms can be neurological (hyperviscosity syndrome) because an increase in blood volume increases viscosity.

There are two categories of polycythemia - relative and absolute. Relative polycythemia is seen with severe dehydration when blood volume is not elevated but plasma volume is decreased. Absolute polycythemia occurs when there is an actual increase in RBC volume. Polycythemia can be further broken down into primary (myeloproliferative disease) and secondary (resulting from another disease process). Polycythemia is considered secondary in cardiac patients, resulting from excessive stimulation of the hormone erythropoietin, which is the main hormone responsible for RBC production.

In cardiology, polycythemia is often found in patients with right to left shunting disorders that cause a reduction in the circulation of oxygenated blood (i.e., ventricular septal defects, reverse patent ductus arteriosus (PDA), or Tetralogy of Fallot). Patients with advanced cardiac disease or congestive heart failure or who have obstructive pulmonary disease are also at risk of developing polycythemia.

Though there are therapies that can suppress the production of red blood cells (often chemotherapeutic agents), an initial phlebotomy can help reduce blood cell volume and relieve patients' symptoms. Oftentimes this is a short-term fix and periodic phlebotomies are required.

A large butterfly catheter is most commonly used for this procedure. The typical site for the blood draw is at the jugular vein. Chemical restraint may be necessary depending on the patient but is often not required. The amount of blood to draw is typically calculated using the following formula:

Blood removed (mL) =

(Weight [kgs] x 0.09) x 1000mL/kg
(actual PCV-desired PCV)

The blood volume removed should not exceed 10-20mL/kg. The side effects of removing too much blood at one time can include hypoxia, syncope, and seizures. Following the procedure and depending on the hospital's preference, either the patient's plasma or isotonic fluids are used as a replacement. Isotonic fluid should be equal to the blood volume removed and can be administered either intravenously or subcutaneously.

Phlebotomies can be a very useful procedure for symptomatic patients with polycythemia. Phlebotomies are a routine procedure that can quickly provide patients with temporary relief of their symptoms and can be performed in lieu of instituting oral chemotherapeutic agents or conducting a further diagnostic workup.

References

McDonell, J. (2019, March 18). Polycythemia. Retrieved June 22, 2020, from https://www.vetfolio.com/learn/article/polycythemia

DID YOU KNOW?

We're Presenting at the IVECCS 2020 Virtual Conference

In light of the ongoing COVID-19 pandemic, after careful deliberation, the Veterinary Emergency and Critical Care Society board has decided to have an all virtual IVECCS 2020 experience September 12-14.

Our hospital manager, Danielle T. Russ, LVT, BS, BA, AS, will present two workshops:

9/12/20 - 10:15am-11:15am Session #182

Staff-Patient Ratios

Balancing improved patient outcomes and staff well-being with financial sustainability. Is this possible?

9/14/20 - 9:00am-12:30pm Session #381 (with Jessica Brotherton)

Problem Solving Through Brainstorming and Networking

Social Media Dilemmas

Staff Retention

Self-Management

Conflict Resolution

To register for the conference, please click here. You do not need to be a VECCS member to attend! To review the entire program, click here. To learn more, click here.

COVE Seaside CE Series 2020 has been cancelled.

Out of concern for the health and safety of attendees, speakers and sponsors during the ongoing COVID-19 pandemic, we have made the difficult decision to cancel Seaside CE 2020.

COVE Seaside CE Series 2021 is tentatively scheduled for the week of May 23-29, 2021 with exact dates and times TBD.

We appreciate your understanding and hope everyone stays well. Looking forward to seeing you for Seaside CE 2021 at a brand new venue, The Regency Royale.

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