Meet Pierre! He’s a handsome, high energy, much loved, 3 ½ year old Pointer Mix that was rescued from a Turkish rescue group and adopted in May 2018. Just days after his adoption, a loud heart murmur was heard and he was referred to Cardiac Care for Pets (CVCA) at The Regional Veterinary Referral Center for further evaluation. No outward cardiac symptoms were noted. He was very energetic and loved to chase squirrels and play with other dogs at the park.
On evaluation, a loud grade IV/VI heart murmur was heard, his pulses were weak, and he was thin. An echocardiogram (ultrasound of the heart) was performed which showed that the valve on the left side of his heart (mitral valve) was getting drawn into the path of blood leaving his heart out the aorta and causing a severe obstruction to the flow of blood. This caused the heart to have to pump against more than double the pressure it normally does and had resulted in severe thickening of the heart muscle on the left side (left ventricle). We were worried for Pierre because when the heart muscle becomes this thickened and overworked, the heart does not get enough oxygen and it predisposes to arrhythmias, fainting, and sudden death. In fact, dogs with an obstruction this severe often die before the age of 3-5 years or develop heart failure later in life.
This schematic of the heart shows the leaflet of the mitral valve getting pulled into the aortic outflow tract (SAM) and obstruction blood out the aorta (Ao). LA: left atrium; MR: mitral regurgitation; left ventricle:LV.
The echo image below shows the mitral valve protruding into the left ventricular outflow tract and obstructing blood flow.
Because the valve is not closing properly there is turbulence in the aorta (yellow mosaic color in the first image below as well as mitral regurgitation (yellow/blue mosaic in the second picture). This is what causes the murmur.
Most cases of obstruction in this region of the heart are a result of a fixed ring of tissue below the aortic valve and are difficult to improve. With Pierre, however, his obstruction was dynamic and we were hopeful that we could reduce Pierre’s obstruction with medications. It was uncertain, however, if or how much he’d respond. He was placed on a drug called Atenolol, which is a beta blocker. This medication reduces the heart’s response to adrenaline and thereby slows the heart rate and reduces the vigorousness of heart muscle contraction. This has the potential to help reduce the pull of the mitral valve into the outflow tract which can reduce the obstruction. It also allows more time for the thickened heart to become oxygenated and reduces the workload of the heart which can help reduce the risk for sudden death. Exercise restriction was recommended since vigorous activity can increase the risk of sudden death in these dogs.
Pierre tolerated the medication well with no noted side effects. He is a very high energy dog and miserable without exercise, so eventually he was allowed to continue normal activity despite the increased risk. He returned to the dog park and chasing squirrels and amazingly never seemed to tire or pass out.
In September 2019, he returned to CVCA for his recheck evaluation. Surprisingly, his murmur had disappeared. He had gained weight and muscle since the initial exam and was now in excellent condition. The echocardiogram was also remarkably improved. The heart that once was severely thickened had returned to normal, and his mitral valve was now closing properly and no longer obstructing the blood leaving the heart. Although we had hoped for some improvement on the atenolol, the dramatic return of the heart to normal was an unexpected and delightful surprise. His prognosis now looks much brighter with the potential of living a normal life span, although he will need to stay on the atenolol indefinitely. Pierre’s family is thrilled that he is doing so well and hopeful that he will be around for a long time to come!
These images show the difference in the heart muscle thickness before (picture one) and after the atenolol (picture 2), as well as lack of turbulence in the second picture compared to the color images above.