INTERACTIVE CASE STUDIES

 
 

MickeyCase Background

 
Name Mickey
Age 14 years
Sex Male
Breed Feline, Domestic Medium Hair
Weight 6.2 kg
Reason for Visit Murmur evaluation, heard by general veterinarian at wellness appointment.
 

Please review Mickey's clinical history.

 
Attitude/Demeanor Calm, alert
Coughing No cough reported
Respirations Eupneic, 32 breaths per minute
Exercise Tolerance No change reported
Sleep Patterns Sleeping well, most of the day
Weight Change (loss or gain) No change in weight
Appetite Normal appetite
Usual Diet Iams® Feline Senior
Vomiting Rare vomiting, 1-2x monthly
Diarrhea None noted
Syncope None observed
Change in urinary habits None observed
Change in drinking habits None observed
 

Please review the results of Mickey's physical exam.

Body Condition Slightly over-conditioned, BCS 6/9
Attitude Calm, alert
Mobility | Gait Not assessed
Posture Normal
Hydration Normal
Body Temperature 102.1 F
Arterial pulse - rate, regularity, intensity 176 beats/min, regular, slightly hyperkinetic
Respiratory Effort 32 breaths per minute, normal effort
Mucous Membranes - Color & CRT Pink
Jugular Venous Pulse & Pressure Slight distension, no pulsation
Abdominal Palpatation Both kidneys have irregular contours on palpation; the rest of the abdominal palpation is non-tender and normal
Lymph Nodes Normal
Oral Cavity Mild gingivitis and plaque
Other abnormalities Slightly rough, dry hair coat
 

Let's auscult Mickey's heart & lungs.

How do you interpret Mickey's cardiac auscultation (recorded at the left parasternal border)?

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The rhythm is regular with a moderate intensity heart murmur appreciated, which is systolic in timing.
A gallop sound is not evident
The rhythm is too regular and not as rapid as would be expected for atrial fibrillation
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Direct HR: 180 bpm

Heart Rhythm: Regular

Intensity of Sounds: Normal, partially obscured by holosystolic heart murmur, grade III/VI

Extra Sounds - Clicks or Gallops: None

Precordial Palpation: Normal

The following are potential diagnosis for you to consider at this time. Based on the history and the physical examination, please indicate the likelihood of each as:
  • High (could explain most or all of the signs)
  • Possible (less likely to explain most of the signs)
  • Unlikely

Functional Murmur

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Hypertrophic cardiomyopathy

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degenerative mitral valve disease

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Hyperthyroidism

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Hypertensive heart disease

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The CEG considers the following differential diagnosis as most likely (and why):

In cats, systolic murmurs commonly arise from structural pathology (e.g. cardiomyopathy, with HCM being the most common) or from functional causes. The term "functional murmur" implies that the heart is structurally normal; these murmurs are seen most often with changes in hemodynamics related to stress/excitement or from alterations in blood viscosity (e.g. anemia). Cats also develop cardiac changes secondary to systemic disease and these may manifest as a heart murmur - systemic hypertension (hypertensive heart disease) and hyperthyroidism (thyrotoxic heart disease) are two common examples. As this cat is 14 years old, it is important to rule out hyperthyroidism even though the clinical picture and history do not fit a classic example of a hyperthyroid cat. It is also important to rule out systemic hypertension in this cat as renal disease is very common in the older cat, which is associated with high blood pressure and may cause secondary cardiac changes that result in a heart murmur. Myxomatous mitral valve disease (degeneration), as occurs in dogs, does not cause significant cardiac disease in the cat and is unlikely to manifest as a grade III/VI heart murmur.

BLOOD PRESSURE

Non-invasive blood pressure

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CLINICAL LABORATORY

CBC with platelet count

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Coagulation profile

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Serum biochemical profile (includes electrolytes)

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Urinalysis

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Serum Thyroxine (T4)

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Heartworm antigen test

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Heartworm antibody test

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Heartworm microfilaria test

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NT-proBNP

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Cardiac troponin-I

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Blood culture

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Thoracocentesis or abdominocentesis for diagnosis or therapy

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DIAGNOSTIC IMAGING (some may require a referral)

Thoracic radiographs

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Abdominal radiographs

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Echocardiogram doppler studies

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Abdominal ultrasound

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ELECTRODIAGNOSTICS (some may require a referral)

ECG rhythm strip or 6 lead ECG

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Ambulatory ECG - Holter ECG or event monitor

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  • You considered the following to be higher priority
    • You considered the following to be lower priority
      • You considered the following to be not indicated

        The CEG considers the following diagnostic tests as the highest priority: 

        There are a few ways to proceed with a case such as this. It is first appropriate to evaluate this cat with a thorough physical examination for any underlying disease and then screen for common causes of functional murmurs; as such, a thyroid level and non-invasive assessment of systemic blood pressure are indicated. Given the age of the cat, routine blood tests for systemic disease such as a CBC, biochemical profile, and urinalysis are reasonable, but unlikely to provide a diagnosis to explain the heart murmur. If all the above are normal, determination of the cause of the murmur would require an echocardiogram. Thoracic radiographs or an electrocardiogram could be performed; however, neither are sensitive for a diagnosis of heart disease and if apparently normal do not rule out cardiomyopathy or other heart conditions. An NT-proBNP test would be reasonable to determine the likelihood that significant heart disease is present. If this test comes back <100 pmol/L, it is unlikely that clinically significant heart disease is present and this may provide useful information to the client debating referral for an echocardiogram. However, it would also be reasonable to forego the NT-proBNP and have an echocardiogram performed to obtain a definitive diagnosis. Indeed, if the NT-proBNP comes back elevated or in a gray zone, an echocardiogram is still the recommended test to determine the cause of this cat's heart murmur.

        Systolic Blood Pressure: 142 mmHg
        Diastolic Blood Pressure: Not available for this case
        Mean Blood Pressure: Not available for this case
        Consensus Statements of the American College of Veterinary Internal Medicine (ACVIM) provides the veterinary community with up-to-date information on the pathophysiology, diagnosis, and treatment of clinically important animal diseases. In 2007, ACVIM published guidelines for the Identification, Evaluation, and Management of Systemic Hypertension in Dogs and Cats in the the Journal of Veterinary Internal Medicine.
        Click here to view and download a PDF of the ACVIM Consensus Statement, Guidelines for the Identification, Evaluation, and Management of Systemic Hypertension in Dogs and Cats.  

        Please review Mickey's thoracic radiographs.

        Click here for ventral dorsal view
        Click here for lateral view

        What is the Vertebral Heart Score (VHS)?

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        Correct.
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        Submit

        Is Mickey's heart enlarged?

        The normal feline VHS is 7.8 /- 0.3. Mickey's heart measures slightly larger than this normal range suggesting cardiomegaly is present.
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        Try again. Please select another answer.
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        Is there evidence of congestive heart failure present (pleural effusion or pulmonary edema)?

        While the heart is enlarged and the vasculature is prominent, there is no convincing infiltrate compatible with pulmonary edema. In addition, the normal respiratory rate and absence of clinical signs do not support that left-sided heart failure is present.
        There is no evidence of pleural effusion and abdominal detail appears appropriate.
        While the heart is enlarged, there is no convincing evidence of pulmonary edema.
        Submit

         
        SERUM CHEMISTRIES
        BUN 34 mg/dL, Normal: 5 - 20 mg/dL
        Creatinine 2.2 mg/dL, Normal: 0.9 - 2.1 mg/dL
        Sodium 144 mEq/L, Normal:146 - 156 mEq/L
        Potassium 3.8 mEq/L, Normal: 3.2 - 5.5 mEq/L
        Chloride 118 mEq/L, Normal: 114 - 126 mEq/L
        ALT 52 IU/L, Normal: 20 - 95 IU/L
        ALP 80 IU/L, Normal: 15 - 65 IU/L
        HEARTWORM
        Heartworm Test Results Not performed
        URINALYSIS
        Urinalysis - USG 1.018
        Urinalysis - Protein Trace
        Urinalysis - Biochemical No significant findings
        Urinalysis - Sediment Evaluation No significant findings
        CBC
        White Blood Cells Not evaluated
        Red Blood Cells Normal PCV - 34%
        Platelets Not Evaluated
        TOTAL T4
        Total T4 Test Results 2.1 micrograms/dL
        NT-proBNP
        NT-proBNP Test Results 497 pmol/L

        How do you interpret Mickey's NT-proBNP results?

        For an asymptomatic cat, a value <100 pmol/L is normal. Values over 100 pmol/L are suggestive of heart disease and further evaluation is warranted.
        In a cat with respiratory signs, a value >270 pmol/L means the respiratory signs are most likely related to heart disease. However, as Mickey does not currently have respiratory signs his elevated value cannot be considered diagnostic for heart failure.
        When screening cats for heart disease, a NT-proBNP value over 100 pmol/L in an apparently healthy cat is consistent with an increased likelihood that the cat does have significant structural heart disease.
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        Your technician just returned with the results of Mickey's echo.

        Please view the video and interpretations that follow.   Click here to watch Mickey's echo
        Subjective - lesions of valves, myocardium, pericardial space There is no pericardial effusion. The mitral valve is being pulled toward the interventricular septum during systole, which is apparent on the slowed long-axis images and supported by the turbulent flow noted on color Doppler in the left ventricular outflow tract.
         LV chamber size and thickness The left venticular walls show symmetrical concentric hypertrophy, measuring thicker than normal. Normal cats have walls that measure 3 to 5 mm in end-diastole with any measurement over 6 mm consistent with hypertrophy. Mickey's left ventricular freewall and septum measure from 6.5 to 8.5 mm in thickness. In addition, his papillary muscles, seen best in the short-axis images, are severely hypertrophied.
         Left atrial size Left atrial size appears mildly dilated, but measurements are required to confirm enlargement. His left atrium did measure slightly larger than normal at 17 mm at end-systole (normal cats have a left atrium that typically measures 11 to 16 mm in diameter).
         LVIDd & LVIDs Left ventricular internal dimensions appear normal to slightly reduced as a consequence of the concentric hypertrophy.
         LV shortening fraction Mickey’s fractional shortening is normal to hyperdynamic. Most cats have a fractional shortening of 35 to 55%; Mickey’s measured 57% likely related to the thick walls compromising his systolic dimension.
         RA, RV and Pulmonary Artery Images of the right heart are not fully shown, but were normal in this cat.
         Effusions There are no effusions apparent.
         Doppler results Color Doppler shows turbulence in the left ventricular outflow tract beginning at the site of mitral-septal contact. This is a consequence of altered left ventricular, papillary, and mitral valve geometry resulting in SAM – systolic anterior motion of the mitral valve.

        The echocardiogram shown in this case study was acquired at the cardiologist, following referral from Mickey’s general veterinarian. The blood work, blood pressure, and thoracic radiographs were all obtained by the general veterinarian prior to referral.

        You're ready to form a diagnosis and treatment plan for Mickey! Please select your answer to each question below.

        What is your diagnosis for Mickey?

        Although hyperthyroidism may result in concentric left ventricular hypertrophy, the normal TT4 value in this cat argues against hyperthyroidism as cause for the changes seen on echo.
        Systemic hypertension could result in concentric left ventricular hypertrophy. However, his Doppler blood pressure was 142 mmHg, which is within the normal range for cats.
        The most likely explanation for the left ventricular hypertrophy, systolic anterior motion of the mitral valve, and resultant murmur is HCM once hyperthyroidism and hypertension are excluded. HOCM is considered a subclassifcation of HCM, diagnosed on the basis of systolic anterior motion of the mitral valve resulting in left ventricular outflow tract obstruction.
        While degenerative changes can occur in the mitral valve of cats, it rarely if ever results in clinical disease. Additionally, mitral degeneration could not explain the left ventricular hypertrophy noted in this cat.
        Submit

        What treatment(s) would you recommend for Mickey?

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        THE CEG RECOMMENDS:

        Mickey has asymptomatic HCM. There are few studies evaluating therapy at this stage of heart disease in cats. In the absence of heart failure, diuretics (furosemide) are not indicated. The use of enalapril in asymptomatic HOCM cats is poorly defined. If the cat is in heart failure, ACE-inhibition is recommended to blunt the up-regulation of the renin-angiotensin-aldosterone system. In the cat with a normally-sized left atrium or slightly enlarged left atrium as in this case, most cardiologists would not initiate enalapril therapy. Additionally, ACE-inhibitors result in vasodilation; obstruction in a cat with HOCM may worsen in response to vasodilation and is therefore typically not recommended. Atenolol is typically recommended in the setting of HOCM by most cardiologists, although there is no scientific evidence in support of this therapy. Either atenolol or no therapy (particularly if the cat is very challenging to medicate) would be reasonable therapeutic recommendations at this time.

         ACTUAL TREATMENT
         Initial Therapy Atenolol was initiated at 6.25 mg orally twice daily; selected for ease of dosing as a ¼ of a 25 mg tablet. A compounded liquid suspension could also have been chosen.
         Diet No change required at this time; there is no evidence for dietary intervention at this stage of heart disease.
         Lifestyle Adjustments None recommended at this time.

         

        Follow-up Treatment: Follow-up is recommended with Mickey’s general veterinarian in 7-10 days to evaluate the response to the atenolol. In general, the response to atenolol is evaluated by monitoring the cat’s heart rate and blood pressure while receiving the medication as well as an assessment for any clinical signs. An excess of beta-blockade would manifest as a lethargic and less active, or even syncopal, cat. On examination of such a cat on too much atenolol, the heart rate is below 140bpm even during stress and blood pressure may be low. Under-dosing of the atenolol is suspected based on an in-hospital heart rate of >170 bpm. In general, a cat on an optimal dose of atenolol will have no change in clinical history and a heart rate in the hospital (e.g. under stress) of 140 to 160bpm. Doses are adjusted to achieve this finding. Once on a stable and appropriate dose of atenolol, a recheck echocardiogram is advised in 3-4 months and then once to twice yearly thereafter to monitor for progressive cardiac enlargement.

        To qualify for CE credit, please answer the following 5 questions.

        Thoracic radiographs can provide a diagnosis of heart disease with high sensitivity and specificity in the cat.

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        Correct.
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        Which of the following is CORRECT, regarding an elevated NT-proBNP (above 100 pmol/L) in a cat?

        Correct
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        Systolic anterior motion of the mitral valve (or SAM) in the setting of hypertrophic cardiomyopathy implies which of the following is TRUE?

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        Correct
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        Therapy for the asymptomatic cat with hypertrophic cardiomyopathy (HCM) should include which of the following?

        Correct.
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        Follow-up for the cat receiving atenolol for the treatment of hypertrophic obstructive cardiomyopathy should include which of the following?

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        Correct
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        EVALUATION SURVEY

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