Colorado State University annual conference

Abstract

Cardiac Evaluation Dr. Joe Bertone presented 8 hours of lecture-a discussion on cardiac evaluation under field conditions. Dr. Begone emphasized that a detailed examination of the cardiac system is essential to a complete physical examination of horses. In addition, it is important to understand the peculiarities of equine cardiac auscultation as related to the large gauge and high vagal tone of the equine cardiac system. Cardiac evaluation is not only important when the client complaint involves the cardiovascular system but is essential to the prepurchase examination, evaluations of poor athletic performance: and in cases where cardiac abnormalities may arise secondary to a primary ailment (such as arrhythmias related to electrolyte abnormalities in cases of diarrhea). Cardiac examination should be performed in as quiet an environment as possible. Common artifactual sounds include respiratory and intestinal noise, muscle tremors and hair robbing sounds. Both sides of the chest and the entire cardiac silhouette should be auscultated. On the left thorax the tricuspid valve sits most cranially followed by the pulmonic, aortic and mitral valves more caudally, Because of the cranial location, under the triceps muscle, of the tricuspid and pnlmonic valves, they are most difficult to discern compared to the aortic and mit/al valves. The tricuspid valve can also be auscultated on the fight side. Heart sounds are generated by the acceleration and deceleration of blood within the heart and great vessels. This movement creates turbulence, which results in sound waves. In the cardiac cycle the fourth heart sound is heard first and is generated by the alrial kick resulting in movement of blood from the atrium into the full ventricle. It is followed by the first heart sound generated by the ventricle contracting and sending blood back against the rigid mitral and tricuspid valves. The third heart sound results when blood rapidly enters the empty atrium and decelerates. The first heart sound is most audible over the mitral and tricuspid valves and is immediately followed by the arterial pulse. With tachycardia the third and fourth heart sounds are less audible and the first and second become more pronounced. However, the overall intensity of all heart sounds is influenced not only by heart rate, but the viscosity of the blood, heart size and heart rhythm as well. Asynchronous closure of the mitral and tricuspid and/or the pulmonic and aortic valve pairs does occur in horses and results in splitting of the first and second heart sounds, respectively. This is not heard in all horses all the time. Murmurs result when there is prolonged audible vibrations that occur during the normally silent period s of the cardiac cycle. Anything that distorts the lanainar flow of blood (enlarged vessels, regurgitant or stenotic valves) results in turbulence of blood flow, vibrations of the he'art and large vessels and subsequently audible noise. Anemia and its resultant decreased blood viscosity may also be associated with murmurs. Physiologic murmurs associated with blood moving into the aorta during systole (ejection murmurs) are common and quiet. Pathologic systolic murmurs are most commonly mitral or tricuspid insufficiency. Pansystolic or diastolic murmurs obscure the first and second heart sounds whereas, holosystolic or diastolic murmurs do not. A continuous murmur is heard all of the time, during systole and diastole. Most clinicians grade murmurs on a scale of 1-6. 1/6 is the softest audible murmur and is heard after careflfl auscultation in a quiet room. 2/6 murmurs are heard within a few seconds of placing the stethoscope on the patient. 3/6 murmurs are heard immediately and are loud but are not associated with a palpable thrill. 4/6 murmurs are loud and have a mild thrill compared to 5/6 murmurs. 6/6 murmurs have a substantial thrill and the murmur is so loud that i t can be auscultated with the stethoscope lifted off of the patient. With valvular insufficiency louder murmurs may indicate greater pathology whereas, with atrial or ventricular septal defects louder murmurs may indicate a smaller hole and, therefore, reflect a greater velocity of blood flow through the defect. Physiologic murmurs are also known as functionalorilmocentmurmurs. They may occur during either systole or diastole and generally are grade 3 or lower. A squeak is an early diastolic, musical murmur usually heard best over the aortic or mitral valves. It is associated with rapid atrioventficular blood flow and is generally not associated with cardiac disease. Systolic clicks may be heard between the first and second heart sound; they too are generally not associated with