Wednesday, October 16, 2013

Three things I learned: staging heart disease in dogs

CKCS teething
Cavalier King Charles Spaniels are at higher risk of developing congestive heart failure secondary to mitral valve disease. 
Heart disease and heart failure are common in companion animal practice, particularly in canine patients. So I am always interested to hear someone's take on heart disease. Dr Rebecca Stepien, from the University of Wisconsin, recently gave a webinar on Diagnosis and Staging of Canine Heart Disease: Deciding When and What to Treat, hosted by Boehringer Ingelheim.

She presented a nice review of the epidemiology, namely that chronic valvular heart disease (CVHD) accounts for around 70 per cent of cases, with dilated cardiomyopathy (DCM) accounting for 8-10 per cent. In Dr Stepien’s area, heart worm disease accounts for 13 per cent of canine heart disease. Around 80 per cent of heart disease (ie DCM and CVHD) will cause left sided heart failure. 

Mitral valve disease is more common in small breeds, especially terrriers, cavaliers and miniature poodles, while DCM is more common in Doberman pinschers, boxers, bulldogs, mastiffs, newfoundlands.

According to Dr Stepien, ANY dog (small or large) can have valvuar disease but small dogs are unlikely to have DCM.

She emphasised the distinction between heart disease, that is a physical or functional abnormality of any part of the cardiovascular system, and heart failure, where low cardiac output or sodium/water retention leads to clinical signs.

Heart disease does not typically require treatment but does require monitoring, ie it is pre-clinical (the exception is Doberman pinschers where onset of heart failure (HF) is delayed with administration of pimobendan.

Clinical signs of heart failure include dyspnoea, cough, exercise intolerance, fatigue, collapse/syncope and cold extremities. BUT a cough in an animal with HD may be due to left atrial enlargement. Coughing due to LA compression of the airways is a sign of cardiomegaly, not HF per se.

On physical examination these animals often have a heart murmur (n.b. very young athletic dogs can have a non-pathologic murmur), gallop rhythm pulse abnormalities (e.g. weak pulse), jugular distension and abdominomegaly (due to hepatomegaly and/or ascites).

I liked Dr Stepien's logical approach to thoracic radiographs in dogs with HD and HF. Left atrial enlargement is always present in HF. If heart disease is present you see chamber enlargement without pulmonary infiltrates and no vascular engorgement.

According to Dr Stepien, the radiographic signs of HF, in the order in which they appear, are:
  1. LA enlargement (also with HD)
  2. infiltrates in the caudo-dorsal lung fields
  3. infiltrates in the caudo-ventral lung fields
  4. infiltrates in the cranial lung fields 

-     With treatment these resolve in the reverse order, ie from 4-1.

Staging HD is important to determine when intervention is required, and because it is a progressive disease. She talked about staging heart disease.
Stage
Underlying disease
Clinical signs
A
High risk but no known injury (eg breed predisposition)
No clinical signs
B1
Minimal remodelling
No clinical signs
B2
Significant remodelling
No clinical signs
C
Structural injury
Current or past clinical signs
D
Structural injury
Refractory signs

According to Dr Stepien, once dogs are diagnosed as in heart failure and treated accordingly, they typically stay out of failure for 6-9 months before they have a problem and may live out two years with aggressive monitoring and treatment. (In my experience it varies significantly between dogs).

She also talked about treatment according to stage which I found useful.

Staged treatment

Stage
Treatment
A
Client education/screening programs
B1
No therapy
B2
Controversial whether to treat or not. Definitely treat Doberman DCM with pimobendan.
C
Triple therapy: diuretic + pimobendan + ace inhibitor, +/- spironolactone, anti-arrhythmics – digoxin? Beta blocker?
D
ACEI +spironolactone+pimobendan+digoxin ?beta blocker? Arterial vasodilator? Rescue nitroprusside/dobutamine

1 comment:

  1. That's really interesting Anne. I usually start "double" therapy - pimobenden and diuretic and then go to triple (add in ACE inhibitor) as progresses, often due to cost restrictions- but if it's a better idea to initially institute triple therapy then i'd definately rather do that. Something to look into methinks...

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