One of the rare complications of myxomatous mitral valve disease (MMVD) is the rupture of the left atrial wall. To date, the author has seen two cases.
Why and how does it occur?
As MMVD progresses, the left atrium enlarges to accommodate the backflow of blood from the left ventricle. The pressure within the left atrium increases, and the atrial wall weakens. When the weakened left atrium can no longer handle the increased pressure, the weakest point of the wall tears. Blood leaks into the pericardial sac (a membrane surrounding the heart), causing pericardial effusion.
The affected dogs show weakness and may faint (syncope).
On ultrasound, a blood clot or thrombus can be seen within the pericardial sac.
A blood clot may also be present on the left atrial wall.
In a study by Czech et al (in year 2024), the mortality associated with left atrial tear was high during the first week. However, if the dogs survived the acute phase, their long-term survival did not differ from dogs with MMVD of similar severity that had never been diagnosed with a left atrial tear.
In Dec 2023, the author attended to a dog which had left atrial tear attributable to stage D MMVD. The dog is still alive at the time of writing (145 days post).
