Approach to a new murmur in a cat Terri DeFrancesco, DVM, DACVIM (Cardiology), DACVECC NCSU College of Veterinary Medicine, Raleigh, NC

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1 Approach to a new murmur in a cat Terri DeFrancesco, DVM, DACVIM (Cardiology), DACVECC NCSU College of Veterinary Medicine, Raleigh, NC One s approach to the diagnostic work up of an asymptomatic cat with a murmur is highly dependent on its age. In a kitten, a soft murmur could be an innocent flow murmur associated with a high heart rate and relative anemia. An innocent murmur should resolve by 6 months of age. If the murmur persists, then a congenital heart defect is most likely. A murmur in a young adult cat is most commonly caused by hypertrophic cardiomyopathy (HCM). The diagnostic challenge with feline HCM is that many cats may not actually have murmurs or other abnormalities. A study out of Virginia Tech suggests that physical examination is an insensitive test to identify cats with HCM and that as many as 16% of cats in the general population may have HCM. Conversely, many cats with heart murmurs may not have a cardiomyopathy. A possible cause for a parasternal murmur in a cat is dynamic right ventricular outflow tract obstruction (DRVO) which is a physiologic cause of systolic murmurs in cats attributable to RV systolic narrowing in a high cardiac output state. Cats with new onset heart murmurs that are older than 7 years old should have a blood pressure, laboratory work to rule out systemic disease such as anemia and renal failure, and hyperthyroidism. Older cats are more likely to have systemic disease (than primary cardiomyopathy) affecting the heart such as hypertension, hyperthyroidism or possibly anemia as the cause of the murmur. In one study, 80% of cats with systemic hypertension had an auscultatory abnormality (murmur or gallop). While primary cardiomyopathy (hypertrophic is most common) can affect cats of any age, it s most common in young or mid adult cats. Additionally, it s should be emphasized that HCM is a diagnosis of exclusion. More specifically, the diagnosis of HCM is defines as left ventricular hypertrophy in the absence of diseases that cause left ventricular hypertrophy. Both systemic hypertension and hyperthyroidism cause left ventricular hypertrophy so it is CRITICAL to rule out. These diseases are treatable and reversible.

2 When to do an NTproBNP? A helpful diagnostic tool in identifying cats with significant heart disease regardless of age or etiology is NTproBNP, a cardiac biomarker. It is elevated in cats with clinical and preclinical heart disease. Our understanding of the role of NT-proBNP in cats is still evolving, but early studies suggest that the sensitivities and specificities may be even better in the cat than in the dog. ProBNP should be of great utility as a relatively lower cost screening test for the cat with a murmur or a cat without a murmur. The IDEXX probnp assay is available as a SNAP test or send out test. The cost of the send out test is reduced when combined with complete blood work. The SNAP test is quite affordable. The cost to the DVM is ~ $11 per test. ProBNP has been shown to be elevated in cats with moderate to severe HCM, hypertension with renal disease and in cats with hyperthyroidism. A negative SNAP test or < 100 on the send out rules out significant heart disease. It s possible to have mild heart disease with these low values. When to recommend an ECHOCARDIOGRAM? An equally as important question as to when to recommend an echocardiogram is WHO should perform the echocardiogram in the asymptomatic cat with a murmur. Cat echo s are hard and I would advise spend my client s money wisely and be sure you have a skilled echocardiographer perform the echocardiogram for a murmur evaluation, especially in a young cat. In a symptomatic cat, a focused echo by a non-specialist is an indicated test that will help expedite an accurate diagnosis. In the older cat, once systemic diseases have been identified, then echocardiography is still an indicated diagnostic test. That said, an echo may not be necessary if hyperthyroidism or hypertension have been identified especially in a cat belonging to a cost conscious client. Echocardiography will better determine the risk for heart failure and may provide corroborative evidence of hypertension, hyperthyroidism or HCM. With systemic hypertension, we usually see aortic dilation often times with aortic insufficiency, mild left ventricular hypertrophy, and variable left atrial enlargement. The echo findings in hyperthyroidism are similar to HCM with the exception of a non dilated LV internal lumen. The echocardiographic criteria for the diagnosis of HCM is an interventricular septum or left ventricular free wall thickness of 6 mm or greater in the absence of any disease that would cause left ventricular hypertrophy. Early HCM diagnosis is not always straightforward as segmental hypertrophy or papillary muscle hypertrophy may be present. Serial monitoring with repeated echocardiograms of equivocal cases is warranted. That said, care should be taken not to over interpret HCM in a hypovolemic cat or in a cat that has mild mitral valve insufficiency with no LVH. Special Doppler echocardiographic techniques may be helpful for the borderline case.

3 What about chest x-rays? Typically, thoracic radiographs are not very helpful for the diagnosis of preclinical disease in cats but are helpful as baseline studies to be used for comparison in the event the cat did present for shortness of breath or develop an arrhythmia. That said, I am more likely to perform thoracic radiographs in the older cat with a murmur. The radiographs will ensure no surprises (occult neoplasia or airway disease) and can provide corroborative evidence of hypertension (redundant aorta). What about blood pressure? Cats with new onset heart murmurs that are older than 7 years old should have a blood pressure measured in a non stressed environment. Blood pressure (BP) measurement is rapidly becoming a routine diagnostic and monitoring tool in many veterinary practices. As some of you have already experienced, the measurement and interpretation of BP measurement in veterinary medicine is not always straightforward. The following discussion includes an overview of the indications for BP measurement, various modalities used to obtain BP, some tips for an accurate measurement as well as some guidelines for interpretation. Noninvasive BP measurement can be obtained by either Doppler ultrasonography or oscillometry. These NIBP modalities cause little discomfort and with minimal training can result in clinically useful information. Various studies have compared these NIBP measurements to the gold standard (direct BP) and to each other with varying results. In general though, most studies do report that NIBP measurement are not 100% accurate and should be interpreted cautiously. Repeated values over time and an average of 3-5 measurements improve the accuracy of NIBP. The Doppler BP modality is preferred by NCSU. Experimental studies suggest that the Doppler systolic reading may be closer to the mean BP when compared to direct BP recordings. Conditions commonly associated with hypertension include: Renal disease/ protein losing nephropathy, Hyperthyroidism, diabetes mellitus, and essential or primary hypertension.the ACVIM consensus statement on systemic hypertension defines it based on a combination of the BP recording and target organ injury. Hypertension: Cat with systolic doppler BP > 170 mmhg with target organ injury Cat with repeatable systolic doppler BP > 200 mmhg and no target organ injury Cat with BP mm Hg with no target organ injury - Monitor closely SOME EASY STEPS FOR AN ACCURATE NIBP MEASUREMENT 1. Practice, practice, practice. 2. Minimize patient stress: a. Perform BP after several minutes of acclimatization to a QUIET environment. Owner present if possible.

4 b. Have everything ready before taking BP (inspect cuff for size 40% of circumference of leg/tail and inspect for no leaks) c. Consider patient position. Make sure pet is comfortable. Sternal recumbency is best. d. Go slowly and handle leg/tail gently. e. Be ready to turn down volume if lose Doppler signal or if animal moves. 3. Select BP site based on animal disposition and conformation. I like the coccygeal artery for most cats and long tailed dogs. The front leg palmar digital artery is also nice for friendly short tailed animals. The dorsal pedal artery, in my experience, is the least reliable. A good rule of thumb is to pick an area on the limb/tail that is uniform in diameter and doesn t taper. 4. Shave over artery (especially for Doppler BP) if needed for longhaired animals. (Most cats) Wait a few minutes to start BP measurement. 5. Inflate cuff first before placing Doppler probe to ensure good working condition. 6. Place Doppler probe over artery, distal to the cuff, with plenty of gel for a good signal. 7. Optimize signal with small motions and varying pressures on the probe. 8. Once pulse signal is optimized, inflate cuff slowly to about 20 mmhg past the occlusion of the artery (when no signal heard). 9. Release the cuff pressure slowly and the systolic BP is the reading on the manometer when the Doppler signal is first heard. The diastolic BP is not accurately measured with Doppler. 10. Deflate cuff completely and repeat at least 2-3 times more until a minimum of three consistent readings are obtained. Disregard a measurement if very different from others. The measurements should not vary by more than 10%. 11. Be consistent: record cuff size, and site of BP measurement for future measurement. 12. Pulse rate MUST match if using oscillometric technique. COMMON SOURCES OF FRUSTRATION WITH NIBP MEASUREMENT: 1. High BP measurement is an aggressive cat: These are difficult situations. One must use all clinical finding to determine if this cat is truly hypertensive. Look for evidence of target organ injury such as left ventricular hypertrophy, renal insufficiency and retinopathy. If no evidence of target organ injury, re-evaluation at another visit is advised ensuring that all is done to minimize patient stress. Sometimes a home BP may be helpful. However, a cat whose BP is consistently over 200 mmhg is very suspicious for hypertension and should be watched carefully. 2. Repeated BP measurements are widely disparate: This is a common problem associated with operator inexperience or a stressed patient. Remember to be consistent. Try to measure the BP in just one site with a specified cuff size. Keep a log in the medical record to enable consistency. My bias is usually to believe the lower values because the higher measurement may be associated with white coat effect. Repeat the BP measurement on later in the day or on another day ensuring that all is done to minimize patient stress. 3. BP measurement appears too low, can I trust it?: Another difficult situation. This is most often encountered in the animal undergoing anesthesia. Feel the pulse manually and repeat the BP measurement. Your bias should be to believe the value especially if the animal is at risk for hypotension (e.g., cardiac disease, sepsis). Try a reduction of the inhaled gas vaporizer setting or evaluate the BP response to a fluid challenge. 4. Arrhythmia or very slow heart rate: Irregular heart rhythms such as atrial fibrillation can be problematic for NIBP to obtain a good BP measurement. I find the Doppler BP more reliable in these settings since I can hear the beat- to- beat and BP variation. 5. Animal is moving or trembling excessively: In my experience the tail is the best place to get the BP if an animal is shaking a lot. Be sure the animal is as comfortable as possible.be patient.

5 One can also try to train the animal to getting his BP taken by giving the owner a cuff to wrap around his tail or leg in his home environment. WHAT S NORMAL BLOOD PRESSURE IN CONSCIOUS CATS? Mean BP Measurements in Normal Non- Sedated Cats Modality Number Systolic Diastolic Mean Oscillometric Bodey JSAP 1998 Doppler NA NA Sparkes JVIM 1999 Direct/Telemetry Belew JVIM 1999 Oscillometric Sansom AJVR < 5 yr 5 < 10 yrs 10 yrs