The thrill of arrhythmias

In the veterinary environment, most team members are familiar with finding a heart murmur in a patient. But what is a heart murmur, and how serious is this condition? What can you do to advocate for the best cardiac care for your patient?

Understanding murmurs

Murmurs are heard by the veterinarian or technician during the auscultation portion of a physical examination. When listening to the heart with a stethoscope, the practitioner should take their time to avoid missing more subtle sounds. The auscultation should be performed in a quiet environment with minimal background noise. First, the precordium, or the outside of the thorax over the heart space, is palpated. Next the apical impulse (the heartbeat against the chest wall) is located, usually felt on the left hemithorax at around the fifth to sixth intercostal space. The veterinarian or technician should also palpate the precordium for palpable thrills, which can feel like a buzzing on your fingers, and often indicates a very strong murmur.

When we listen to the patient's heart, we divide the sounds into transient sounds and murmurs. Transient sounds encompass normal, as well as abnormal, sounds within the heart. The “lub” and “dub” we hear are the first and second heart sounds, which are heard in all animals and considered to be normal. Additional sounds are considered abnormal and referred to as arrhythmias.

For the purposes of this piece, we will focus on murmurs and what they sound like. When a murmur is heard during auscultation, there is an extra swishing sound caused by turbulent blood flow within the heart. The turbulence creates vibrations that can be heard, and sometimes felt as a thrill. In a normal heart, we do not hear this extra “swishing” noise since blood is flowing in a smooth, unidirectional fashion.

Murmurs are graded by intensity with a scale from 1-6, one indicating the least severe, and six being the most severe. Grade 1 murmurs may take several minutes to hear, and even with an experienced ear, may be missed. Grade 2 murmurs are softer, focal murmurs that are more difficult to locate. Grade 3 is intermediately loud and heard in more than one location. Grade 4 murmurs are louder, and easier to hear anywhere on the thorax. Grade 5 murmurs are loud, but also include a palpable thrill. Grade 6 murmurs are the loudest, include a palpable thrill, and can be heard even with the stethoscope not flush with the body wall. It is important to note that while most murmurs are indicative of some form of cardiac disease, the murmur intensity does not directly correlate with the severity of disease.

The murmur's link to cardiac disease

As mentioned earlier, a murmur does often signal the presence of cardiac disease, however the seriousness of the disease can vary greatly. We'll go through some of the more common causes of a murmur and what they can mean for the patient.

> Mitral valve regurgitation is the most common murmur heard, especially in cats and small breed dogs1. The murmur will be heard over the left apex of the heart, with variable loudness. Causes can include endocarditis, dysplasia, endocardiosis or volume overload.

> Tricuspid valve regurgitation murmurs are very similar to mitral regurgitation in their quality, pitch and timing. However, they are usually loudest in the right hemithorax. An echocardiogram is the best way to differentiate between tricuspid and mitral valve regurgitation since they can be very difficult to differentiate upon auscultation alone.

> Subaortic and pulmonic valve stenosis can both be heard at the left heart base. It can be hard to differentiate between the two on auscultation alone. Both conditions are caused by a congenital heart defect. Subaortic valve stenosis is more commonly seen in Golden Retrievers, Newfoundlands, Boxers, as well as other large breeds. Bulldogs, Terriers, Labrador Retrievers and Boxers are more likely to exhibit pulmonic valve stenosis2. The outcome can range greatly from a murmur alone, to an arrhythmia, to congestive heart failure. Some visible signs in these patients may include abdominal distension, exercise intolerance and/or dyspnea.

> Patent ductus arteriosus (PDA), murmurs are continuous and heard in the left axillary region. This is also a congenital defect, and often can be diagnosed by auscultation. Heart failure can be a sequela to PDAs, in which the patient may appear weak, cough and/or have shortness of breath.

> Loud murmurs heard in the right basilar region are consistent with ventricular septal defects. Patients with ventricular septal defects may have dyspnea, exercise intolerance, fainting and/or cough.

Why is consultation with a board-certified cardiologist so important?

A board-certified cardiologist has not only graduated from veterinary school, but also has 3-5 years of cardiac-specific training through a residency and internship, and undergoes 2 years of extensive examinations. With this vast knowledge, these cardiologists are able to perform the most thorough echocardiogram and cardiac examination, and provide the most optimal outcome for your cardiac patient.

With the utilization of echocardiography, the cardiologist is able to evaluate the size of the heart, thickness of the heart walls, pumping capacity, abnormalities in blood flow, valves, and/or the pericardium.

Most cardiac diseases are able to be diagnosed with the use of echocardiography by a board-certified cardiologist. Moreover, many patients can be successfully managed by a specifically tailored medication plan.

Your role

Since finding a heart murmur can point towards a multitude of disease processes, it is very important to be proactive when educating a client. The sooner a definitive diagnosis is made, the quicker the patient can be treated and potential furthering of cardiac disease can be managed and slowed down. Many patients do not show significant signs of heart disease until it has advanced to a much more severe state. Encourage your clients to pursue consultation with a board-certified cardiologist early on in the disease process, and they will thank you for giving them the gift of many more quality years with their loved one.

References:

1. 'Leaky Valve Disease' of Older Dogs: Degenerative Atrio-Ventricular (Mitral and Tricuspid Regurgitation) Valve Disease." Cornell University: College of Veterinary Medicine. Cornell University Hospital for Animals, 2014. Web.

 2. Ware, Wendy A. “Congenital Cardiovascular Diseases.” Cardiovascular Disease in Small Animal Medicine. London: Manson/The Veterinary, 2007. 228. Print.