Case Studies In Small Animal

Cardiovascular Medicine

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Case 34

Presenting Complaints

bulletThree-month Recheck

Pertinent History

bulletChristopher was presented to the Cardiology Service for a recheck of an epicardial pacemaker placed 3 months ago. The owner reports that Christopher is doing well with no episodes of collapse. He has a good appetite and no C/S/V/D/PU/PD. An annual physical exam performed by the referring DVM last month showed that his heart rate was ~100bpm. He is currently receiving diltiazem 7.5mg PO TID for his previous supraventricular tachycardia. He also has a history of LV myocardial failure diagnosed by echocardiography.

Physical Examination

bulletGen: BARH, T=100.2, P=100, R=50.
bulletInt: full, clean coat, no evidence of fleas, but two ticks removed from the pinna of the left ear and caudal to the right ear.
bulletEENT: clear sclera, cornea, conjunctiva, and anterior chamber. No ocular d/c. Ears-clean with no d/c AU. Nose moist with no nasal d/c. Mouth - mild gingivitis and calculus.
bulletMS: BCS 5/9, no gait abnormalities
bulletCV: III/VI left parasternal systolic murmur, irregular rhythm with HR ranging from 100 to 160bpm, CRT=1s, mm pink and moist, pulses strong and synchronous.
bulletResp: clear lung sounds in all fields.
bulletGI: smooth intestinal loops, no masses or organomegaly.
bulletGU: very small, smooth bladder. Kidneys smooth.
bulletNS: appropriate mentation, full exam not performed.
bulletLN: mandibular, prescapular, and popliteal all <1cm.

Problems

bulletArrhythmia
bulletMyocardial failure
bulletIII/VI systolic murmur
bulletThird degree AV block with pacemaker

Clinical Diagnoses

bulletThird degree AV block
bulletEpicardial pacemaker
bulletTrivial diastolic mitral regurgitation
bulletMyocardial failure
bulletMild aortic insufficiency
bulletSupraventricular tachycardia (controlled)
bulletSeptal aneurysm

Comments

bulletECG: HR varied from 100-160 bpm. His own rhythm at the higher heart rates is difficult to distinguish from a regular sinus rhythm and a slower supraventricular tachycardia. Pacemaker was pacing 13% of the time and sensing 87% of the time. Pre values showed amplitude=4V, pulse width=0.5ms, and a battery life of 99 months. Post values were changed to amp=2.0V, PW=0.35ms, with a subsequent battery life of 127 months. These changes were made based on a 2.8 times safety margin according to a strength duration test. The lower rate was set at 100bpm and the refractory period at 150ms.
bulletECHO: IVSd=4.1 mm, LVEDD=20.9 mm, LVFWd=3.8 mm, LVESD=16.3 mm, FS~22%. LVEDD based on 4 chamber view=18.0 mm. Findings showed continued myocardial failure (ESD 15.1 mm Nov 7, 12.8 mm Nov 21, 16.3 mm today, EDD 21.2 mm Nov 7, 18.4 mm Nov 21, 2.09 or 18.4 mm today). Trivial diastolic mitral regurgitation and mild aortic insufficiency are noted. A thin membrane along the interventricular septum beneath the aortic valve is identified. This is likely a septal aneurysm that has been overlooked on previous examinations. It is of no clinical significance. It is, however, likely the cause of Christopher's systolic murmur.
bulletConclusionsl: Christopher still has myocardial failure that appears to be progressing since his LVESD increased from 13 mm previously to 16 mm today and EDD from 18 mm to 21 mm or 18.4 mm today with a decreased fractional shortening of ~23%. The septal aneurysm appeared to be where a VSD would typically be, but no flow traversed the interventricular septum. Turbulent flow was identified in this area along with mild aortic regurgitation. This is likely the source of Christopher's murmur. It is still unclear if Christopher's "own rhythm" is normal sinus or a slower supraventricular tachycardia. Also, the cause of Christopher's myocardial failure is unclear. It is likely that the underlying cause of Christopher's conduction disturbance is also causing his myocardial failure. Previously submitted taurine levels were within normal limits.

Discharge Summary

bulletChristopher was presented to the Cardiology Service for a recheck of an epicardial pacemaker placed 3 months ago. The owner reports that Christopher is doing well with no episodes of collapse. He has a good appetite and no C/S/V/D/PU/PD. An annual physical exam performed by the referring DVM in last month showed that his heart rate was ~100bpm. He is currently receiving diltiazem 7.5mg PO TID for his supraventricular tachycardia. He also has a history of LV myocardial failure diagnosed by echocardiography.
bulletOn physical exam, Christopher had a III/VI left parasternal systolic murmur and an irregular rhythm with HR ranging from 100 to 160bpm. His CRT was 1s, mm were pink and moist, and pulses were strong and synchronous.
bulletAn recheck echocardiogram showed that Christopher still has third degree AV block which is being effectively managed with his pacemaker and myocardial failure that appears to be progressing. His LVESD has increased from 13 mm to 16 mm today and EDD from 18 mm  to 21 mm today with a decreased fractional shortening of ~23%. The cause of Christopher's myocardial failure is still unknown at this time.
bulletAn interventricular septal aneurysm was identified which appeared to be where a VSD would be. It was difficult to determine if flow crossed this membrane. This is likely the cause of his systolic murmur.
bulletA recheck ECG was difficult to determine if his own inherent rhythm was a regular sinus rhythm or a slower SVT.
bulletChristopher was discharged with instructions for his owner to continue the diltiazem @ 7.5mg PO TID since it appears to be slowing his heart rate from the previous 240 bpm. He will return for a recheck in 3 months.

Mark D. Kittleson, D.V.M., Ph.D. All rights reserved.