An Echocardiogram is an important diagnostic tool in veterinary medicine, but is also incredibly important in the Sphynx breed, as well as many others, in monitoring heart health proactively on a routine basis. In order to better understand what all of the measurements deduced by an echocardiogram mean, let’s first clarify some important terms and abbreviations you will commonly see on the HCM screening forms.
Diastolic and Systolic are both in reference to blood pressure. Diastolic blood pressure measures the force the heart exerts on the arteries in-between heart beats, while Systolic blood pressure measures the force the heart exerts on the arteries during each heart beat.
A heart murmur is an abnormal sound in the heart, and is graded on a scale of 1 through 6 in severity. Murmurs can be physiologic (innocent) or can be pathologic (caused by disease). They are usually heard in systole (while the heart is beating/contracting) but can also be heard in diastole (while the heart is relaxed).
There are two Echocardiography modes commonly used in cats; M-Mode and 2D. M-Mode shows a one dimensional view of all structures that reflect the ultrasound waves, along one ultrasound line, while 2D is exactly that, a two dimensional view of a cross section of the heart viewable in real time.
The following is a list of the abbreviations for the individual structures of the heart the cardiologist will be measuring to determine if there are any signs of cardiac disease, or if the heart appears to be healthy and functioning properly at the time of the examination;
IVSd = Interventricular septum thickness at end-diastole
LVIDd = Left ventricular internal dimension at end-diastole
LVFWd = Left ventricular free wall diameter during diastole
IVSs = Interventricular septum thickness at end-systole
LVIDs = Left ventricular internal dimension at end-systole
LVFWs = Left ventricular free wall during systole
SF = Shortening fraction
Ao = Aorta
LA = Left Atrium
LA/Ao = Ratio of the left atrial dimension to the aortic annulus dimension
What does “Subjective left atrial size” mean? This is the Cardiologist’s visual assessment of the size of the left atrium.
What is Systolic Anterior Motion of the Mitral Valve? Systolic anterior motion of the mitral valve, SAM, is the most common cause of a heart murmur in cats with HCM. Often times, it’s a precursor to an actual HCM positive diagnosis. This occurs when the anterior mitral valve leaflet gets pulled into the left ventricular outflow tract during systole (when the heart is contracting) usually because of enlarged papillary muscles. The leaflet gets caught up in blood flow and often pushed up against the intraventricular septum. This produces a dynamic (fluctuating) subaortic stenosis (a narrowing) that increases the blood flows velocity and often times produces a turbulence. Sometimes when the leaflet is pulled towards the intraventricular septum this also causes a gap in the mitral valve and causes regurgitation. Interestingly, there are some reports of SAM occasionally being the primary problem, causing secondary HCM.
What is “End-Systolic Cavity Obliteration”? This is when the apical intracavitary space becomes totally filled or occupied in systole, during contractions by the left ventricular muscle. Basically all the space that should be there is filled up by enlarged contracting muscle.
Papillary muscles are pillar-like muscles that are attached to their walls within the cavity of the ventricles. Variations can be normal for some cats, but sometimes these muscles can be our first hint that a problem might be slowly developing.
So now that we know what the abbreviations stand for, here is a table that shows the measurement ranges in millimeters for what is generally considered “normal”.
HCM is a complex and often occult disease, and while a mutation was discovered in 2020 to be contributory to more than half the cases of HCM we see in the Sphynx breed, echocardiograms are still our most useful tool in mitigating this disease. All Sphynx, regardless if they are an active part of a breeding programme or not, should be routinely screened for HCM. Not only are the results potentially useful to the breed, but the results of an echocardiogram can better equip you to address any heart related health concerns your cat might be dealing with and can prolong life as well as improve quality of life.