Congestive Heart Failure In Dogs

- [voiceover] let's talkabout the pathophysiology and diagnosis of dilated cardiomyopathy. if you break down the wordcardiomyopathy you can remember that it's adisease of the heart muscle because cardio stands for heart,

Congestive Heart Failure In Dogs, myo muscle, and pathy disease. so, a disease of the heart muscle. and dilated cardiomyopathy is a specific type of cardiomyopathy.

now, before we get into whatcauses dilated cardiomyopathy, let's first just briefly review some of the normal cardiac or heart physiology. when the heart normally beats the muscles of the ventricles,the bottom part of the heart, those muscles relax causingthe ventricles to expand, and this draws blood in from the atria. then those muscles contractand then that contraction of the muscles ejects the blood

out of the aorta and thepulmonary artery to send the blood either to the body or to thelungs where it gets oxygenated. a couple of terms i wantto just describe here real quick and the first one is systole. and what systole is, isit's the period of time in which the heart muscle is contracting. during systole, blood is being ejected out of the ventricles toeither the body or the lungs. but then the other period of time

in the cardiac cycle is known as diastole. during diastole the muscles of the heart are relaxing and so theventricle size is getting bigger and this is what is drawingblood into the ventricles so the ventricles are filling. so just a recap of that, during systole the ventricles are contracting and ejecting blood out of the heart. and also during that time thatmeans the atria are filling

and then during diastole the atria are emptying the blood intoa relaxed ventricle. so now that we've reviewedthe normal cardiac cycle let's get into the pathogenesisof dilated cardiomyopathy and what i mean by that ishow this disease develops. basically, dilatedcardiomyopathy is caused by a dysfunction in the heartmuscle's ability to contract. and since this is whenthe heart is contracting, which we talked aboutearlier is called systole,

this is known as a systolic failure. so let's see what this looks like. i'm going to adjust thedrawing of the heart here, and now you can see theheart muscle's kind of thin. the walls of the ventricles have gotten a little bit thinner especially down here at the bottom it's a little bit thinner. and this is just drawnin here to demonstrate that the muscle isn'table to contract as well.

so let's see what this lookslike during the cardiac cycle. now the heart is contractingbut it's not able to eject all of the bloodout of the ventricle. normally the ventricleseject somewhere between 50 and 75 percent of the bloodout every time they contract. but now this decreasedability of the ventricles to contract, this systolicfailure, is causing more blood to remain in the ventricle. and if more blood'sremaining in the ventricle

less blood has left the ventricle. so there's a decreased flowto the rest of the body. this is known as adecreased ejection fraction. what happens to compensatefor this ejection fraction is that the chambersdilate and this is why it's known as dilated cardiomyopathy. so how does this compensate for the decreased ejection fraction? it would make sense that the body needs

a certain volume of bloodwith every contraction of the heart and with thedecreased ejection fraction it's getting a lower volume. but if the chambersdilate the total volume of the ventricles increases so even if you have a decreased percentageof this increased volume you have an adequate volume of blood that's actually ejected fromthe ventricles each heart beat. this dilation getsprogressively worse and worse.

eventually not only arethe ventricles just dilated but the atria become dilated as well because of the backup of blood. and it gets to a point where the chambers can't dilate enough. they just become asdilated as they can get. and this is when someonewith dilated cardiomyopathy starts to develop the signsand symptoms of heart failure. these signs and symptoms of heart

failure are due to two processes. they're either due to a decreased ability to pump the flow forwards, which will cause things like chest pain because you're not gettingenough blood to the heart or it may cause someoneto faint and pass out because they're not gettingenough blood to the brain. or you can also have signs and symptoms due to the blood backing up

and kind of backing up behind the heart and you get things like swelling or edema of the legs and abdomenwhich is known as ascites. so what actually are the causesof dilated cardiomyopathy? well, it can be geneticand these genetic causes are due to problems withsome of the proteins in the muscle cells themselves that don't allow them to contract quite as well. but it can also be due to inflammation

of the heart from somethinglike a viral infection. this is known as myocarditis. or it can be due to toxinsthat affect the heart. the most common of these is alcohol. or another unfortunate causeof this is actually pregnancy. we're not exactly surewhat about pregnancy causes dilated cardiomyopathy butthere is definitely an increased risk of developingcardiomyopathy during pregnancy. and then the last one i wantto mention here is idiopathic,

meaning we don't know what causes it. but it's also important to note what are not the causes of dilated cardiomyopathy. specifically, dilatedcardiomyopathy is not caused by ischemic heart disease, valvular heart disease so diseases of the valves of theheart, or hypertension. and it's important to note this because these diseases can cause heart failure

and it has a similar presentation to dilated cardiomyopathy in that the heart dilates and resultsin a systolic failure. but the difference is in those conditions, the heart failure is secondaryto the other condition whereas in dilated cardiomyopathyit's a primary disease of the heart muscle itself. so dilated cardiomyopathy is not caused by ischemia, valvular heartdisease or hypertension.

so now that we've gone over the cause of dilated cardiomyopathy how do we diagnose dilated cardiomyopathy? the first step is going over the patient's history and physical. let me just abbreviate that: h and p. and the signs and symptomsor the history and physical are really just goingto be consistent with heart failure butthere's not many that are

very specific to dilated cardiomyopathy. the next thing is labs andone of the most important labs in any cause of heart failureis something that's known as the brain natriureticpeptide or the bnp. and bnp is elevated inconditions that cause stretching of the heart suchas dilated cardiomyopathy so it`s elevated indilated cardiomyopathy. but that's not very specificas it's also elevated in lots of other causes of heart failure.

so next we're going togo to some special tests. and the first one i wantto mention is an ekg. in the ekg of dilatedcardiomyopathy it's almost always abnormal but the findingsare non-specific. an abnormal ekg doesn't necessarily say someone has dilated cardiomyopathy. but a normal ekg willalmost rule out the disease. so almost everyone withdilated cardiomyopathy will have an abnormal butit's going to be non-specific.

the next one is a chest x-raywhich i'll just abbreviate cxr and this is going to showsomething called cardiomegaly. this just means enlarged heart. it makes sense that if ina dilated cardiomyopathy the heart gets enlarged then in the chest x-ray you'll see a big heart. the next test, and the best test, for dilated cardiomyopathyis an echocardiogram. an echocardiogram is anultrasound of the heart.

in an echocardiogram you can see the dilation of the chambers as well as the decreased ejection fraction. there's two other tests i want to mention but they're not routinely used in the diagnosis of dilated cardiomyopathy. the first one is an angiogram and this is a study that looks that theblood vessels of the heart. and since i said dilated cardiomyopathy

is not caused by ischemia an angiogram is not going to showany signs of ischemia. the last thing i want to mention is a biopsy of the heart muscle itself. in a lot of types of cardiomyopathy biopsies of the heartmuscle are very important and they give you an idea of what the cause of the cardiomyopathy is. and kind of like the ekg the biopsy

is usually going to be abnormal. but it's not veryspecific so if a provider thinks a patient hasdilated cardiomyopathy these are the three majortests to diagnose it. these tests may be helpfulbut are only really used if the provider is tryingto work up the patient for another condition and then they end up realizing that the patienthas dilated cardiomyopathy. so, just remember thatdilated cardiomyopathy

is a dysfunction in theheart's ability to contract. which means it is a systolic heart failure that manifests as adecreased ejection fraction and so the heart will compensateby dilating it's chambers

and that is why it's calleddilated cardiomyopathy. and that it's diagnosed primarily with an ekg, a chest x-ray and the best test for it is an echocardiogram.