Case 1: Syncope versus Seizures
Signalment: 14-year-old MC domestic shorthaired cat
Chief concern: Recurrent seizure-like episodes x 8 months, now occurring several times daily.
History: Episodes are characterized by ataxia, disorientation, opisthotonos, and seizure activity. They are brief (10–30 seconds) and self-terminating. On initial evaluation 8 months earlier, the referring veterinarian heard premature beats and speculated that sotalol should be prescribed; the cat had been receiving sotalol 20 mg PO q 12 h for the 8 months prior to presentation.
Physical exam: Bright, alert, responsive cat. Normal mentation. Normal heart sounds and regular heart rhythm @ 220 beats/minute.
Diagnostic test results: An electrocardiogram revealed normal sinus rhythm/sinus tachycardia. An echocardiogram was unremarkable. Hospitalization with electrocardiographic monitoring (Holter) demonstrated no arrhythmia over a 24-hour period. The patient was discharged after discontinuation of sotalol. Six weeks later, episodes recurred and were more severe. ECGs obtained immediately after episodes showed sinus tachycardia. An event monitor that was placed and triggered during an episode identified third-degree AV block with ventricular standstill lasting up to 25 seconds.
Analysis and conclusion: A permanent epicardial pacemaker was implanted on an emergency basis and episodes resolved.
Learning point: Neurologic disease and severe cardiac arrhythmias, especially severe bradycardias, can produce similar or even indistinguishable signs. The arrhythmia should always be evaluated first, using echocardiography to assess cardiac structure, then electrocardiography until an arrhythmia is convincingly identified or ruled out during an episode. Failure to do so risks anesthetizing a patient for a neurologic work-up, with an arrhythmic crisis under anesthesia.
Case 2: Thromboprophylaxis: When to Treat to Prevent Blood Clot Formation
Signalment: 1-year-old MC Burmese
Chief concern: Incidentally detected heart murmur
History: Routine physical exam revealed new heart murmur. No overt clinical signs. No treatment.
Physical exam: Bright, alert, responsive cat in good body condition. Normal respirations, exam room RR = 24/minute. Grade II/VI systolic murmur, with point of maximal intensity over left parasternum. Regular rhythm @ 220/minute.
Diagnostic test results: Echocardiography revealed moderate, asymmetrical left ventricular thickening (maximal interventricular septal thickness in diastole = 6.7 mm) and moderate to marked left atrial enlargement (2D LA:Ao = 2.2:1, absolute LA diameter = 23 mm; subjectively disproportionate degree of left auricular enlargement; no clot or spontaneous contrast). Mild systolic anterior motion of the mitral valve, and mitral regurgitation, were apparent at higher heart rates.
Analysis and conclusion: Given these findings, an increased risk of thromboembolism could be suspected.
Whether or not to begin treatment with clopidogrel was discussed both from a medical standpoint (absence of supportive evidence; risk associated with atrial enlargement; lower risk associated with hypertrophic obstructive cardiomyopathy, as in this cat, compared to hypertrophic or restrictive cardiomyopathies) and a logistical standpoint (owner ability to administer medication daily; tolerance of the medication [palatability]; lack of quantifiable benefit). This cat’s owners opted to begin treatment with clopidogrel 18.75 mg/cat PO q 24 h.
Learning point: Left atrial enlargement is considered a risk factor for cardiogenic thromboembolism in cats, but efficacy of preventive treatment (thromboprophylaxis) is unknown in cats that have not experienced an episode of thromboembolic disease. Presence of spontaneous contrast (minority of such incidentally detected cases) or of discrete intra-atrial clots (even less common) are logical indications for initiating treatment.
Case 3: Subclinical HCM: What to Do?
Signalment: 12-year-old MC domestic shorthaired cat
Chief concern: Incidentally detected heart murmur
History: Unremarkable past medical history. Routine annual exam revealed newly detected heart murmur.
Physical exam: Bright, alert, responsive cat in good body condition. No evidence of dehydration. Normal respiratory rate and character. Grade III/VI systolic heart murmur with point of maximal intensity over sternum. Regular heart rhythm @ 200/minute. Strong, synchronous pulse.
Diagnostic test results: Echocardiography reveals moderate, diffuse left ventricular hypertrophy, septum thicker than free wall (7 mm and 6 mm, respectively, in diastole). Left atrial diameter within normal limits.
Analysis and conclusion: The incidental finding of a thick left ventricle in a cat raises several important questions.
1. Is it pseudohypertrophy? The effects of dehydration and of tachycardia must be considered or ruled out.
2. Is it hypertrophy due to an extracardiac disorder? Hyperthyroidism, systemic hypertension, and acromegaly must be considered and ruled out if clinically relevant.
3. Is there a structural cardiac reason to explain hypertrophy? Aortic stenosis must be ruled out.
4. Should it be treated? The absence of overt clinical signs makes treatment nonessential because efficacy of treatment has not yet been demonstrated.
Beta-blockade, while logical in patients with persistent left ventricular outflow tract obstruction, has not been shown to alter the course of spontaneous hypertrophic cardiomyopathy in cats. Angiotensin-converting enzyme inhibition (e.g., via ramipril) likewise appears ineffective.
Newer treatment options, be they chronotropic (e.g., ivabradine) or myocardial (e.g., inhibitor of sarcomere contractility) are under investigation. An argument can be made for thromboprophylaxis when the left atrium is enlarged (see above), but not when it is of normal size, as in the present case.
Learning point: Before establishing a diagnosis of hypertrophic cardiomyopathy in a cat with no overt clinical signs, the clinician must consider other explanations for increased left ventricular wall measurements. When such confounders are excluded, treatment generally is considered only when additional factors support it, such as the presence of tachyarrhythmia (for beta-blockade).