A tale of two puppies with a heart murmur

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Delta, an American cocker spaniel puppy, and Macey, a Labradoodle puppy, were referred to Northwest Surgeons in the same week because a heart murmur had been identified by each of their veterinary surgeons at their initial vaccinations even though they were showing no signs of heart disease and, being typical bouncy puppies, they seemed completely normal to their proud new owners. 

The murmurs were similar, with a characteristic continuous, so-called “machinery” sound.    The “machinery” murmur is very suggestive of a heart defect present from birth called a patent ductus arteriosus (pronounced duck-tuss  art-ear-i-oh-suss), but which is usually abbreviated to “PDA”.  Such a diagnosis is obviously a shock to the owner of a bright young puppy, but happily a PDA is one of the conditions that can be completely cured by surgery to close off the abnormal blood vessel.  The earlier it is diagnosed and treated, the better the long term outcome for the patient.  This is one of the reasons why a health check by your veterinary surgeon at the time of vaccination is so important to detect these things so that specialist investigation and treatment can be offered promptly if needed.

In the womb, babies (whatever their species) have a special blood vessel (the ductus arteriosus) which bypasses the lungs because the lungs are not needed in the womb.  However, soon after birth the ductus arteriosus should close off, redirecting blood appropriately through the heart and lungs.  A PDA is what happens when this blood vessel fails to close properly after birth.  The result of a PDA is that blood flows in an abnormal way around the heart and lungs and it is the abnormal flow of blood that causes the abnormal heart sound or murmur. As a result of the blood flowing in an abnormal way, the heart becomes overloaded and without treatment most affected dogs will die of heart failure before 12 months of age.

There are two techniques available to close the PDA:

·       The so-called “open” surgical technique involves opening the chest, carefully dissecting around the ductus then tying it off with non-absorbable suture material.  This is a very delicate procedure as tearing the fragile ductus arteriosus can be fatal.  We are fortunate at Northwest Surgeons to have a very experienced specialist soft tissue surgeon who has performed this operation many times.  As the chest is opened, the anaesthetist has to take over breathing during the procedure using a ventilator.

·       The non-surgical technique requires catheterisation of the heart and a specialised real-time x-ray called fluoroscopy.  This is similar to that used in the investigation of humans with coronary artery disease.  A small incision is made over one of the arteries in the groin and catheters are guided from here through the arteries in the body, into the chest and across the PDA.  Following some initial tests using the fluoroscopy, a special device (called an Amplatzer after its inventor) is passed along the catheter in the arteries and into the PDA.  The Amplatzer is a mesh of wire that folds up to fit in the catheter.  It has memory so as it is pushed out of the catheter it resumes its original shape.  In this case it forms a dumb-bell shape that blocks the PDA, redirecting blood flow in the appropriate direction.  Further fluoroscopy studies are performed after the Amplatzer is placed to confirm successful blockage of the abnormal blood vessel.  This approach has the advantage that there is no need to open the chest, but irregular heartbeats are often seen and again an experienced and well qualified specialist anaesthetist is vital.

Both procedures have similar success rates.  Open surgery usually requires a shorter anaesthetic time than the catheter technique, but recovery from the catheter procedure is faster because there is no need for major surgery to open the chest.  Often the choice depends on the size of the ductus arteriosus and the size of the arteries in the groin.  Only a small handful of specialist referral centres in the UK have the expertise to offer both procedures and the presence of specialists in so many disciplines at Northwest Surgeons allows us treat these patients using the best option for each pet.

Further investigations including echocardiography (heart scan) confirmed the presence of large PDAs in both puppies.  As these puppies were young, it was likely that these would cause premature heart failure and death if not treated properly.  In Delta’s case, the vessels were too small to allow the catheters to pass and she had open surgery.  She recovered well and was discharged three days after surgery.  Macey was much larger and we were able to use the catheter technique to close the PDA.  She was discharged the day following the procedure.

Both dogs returned after one month for re-evaluation.  No murmurs could be detected and an echocardiography examination confirmed closure of the ductus arteriosus in each dog.  In addition, the heart size was smaller as it was remodelling back towards normal from its original overloaded state.  Both dogs are still typical puppies full of beans and the good news for them and their owners is that they should now have a normal life expectancy in full health.

Both cases were referred to Simon Swift, European specialist in veterinary cardiology.  Macey’s procedure was performed by Simon.  Thanks to Catherine Sturgeon, European & RCVS specialist in soft tissue surgery, for treating Delta and to Matt Gurney, European specialist in anaesthesia and analgesia, for anaesthetising both patients.