Veterinary Structure and Function I Practical Manual - PDF

VPP 3215 Veterinary Structure and Function I Practical Manual PRACTICAL HEART AUSCULTATION (HORSES, RUMINANTS & DOGS) Cardiovascular sounds consists of vibrations produced by moving blood, blood vessels, heart structures (valves, muscle) and associated thoracic structures. These sounds may be cha...

VPP 3215 Veterinary Structure and Function I Practical Manual PRACTICAL HEART AUSCULTATION (HORSES, RUMINANTS & DOGS) Cardiovascular sounds consists of vibrations produced by moving blood, blood vessels, heart structures (valves, muscle) and associated thoracic structures. These sounds may be characterized by their timing, duration, intensity (amplitude), pitch (frequency), and quality. Cardiovascular sounds are mainly classified as 1) transients (sounds of relatively short duration), or 2) murmurs which are groups of sound vibrations of longer duration). Murmurs possess a variety of distinguishing characteristics, including intensity, timing, duration, frequency, character, and location. The human ear is not equally sensitive to all frequencies and there is also considerable variation from person to person. In general, the lower the frequency of the heart sound the louder it must be to be detected by the ear. The percentage of the total cardiovascular sound which lies above the threshold of audibility is small which means we hear only a limited percentage of the total sounds produced by the heart and its associated structures. Areas of Auscultation The following figures outline the points of maximum audibility of the four heart valves in the horse. The terms mitral, tricuspid, aortic, and pulmonic are employed as designations for these positions on the thoracic wall. At times, it may be difficult to identify a specific valve area and terms such as right or left cardiac apex or cardiac base are used. 1 VPP 3215 Veterinary Structure and Function I Practical Manual The Stethoscope A quality binaural stethoscope should have comfortable ear pieces angled slightly forward to fit snugly into the ear canals. The best tubing is about 1/8" (3mm) in internal diameter and as short as practical for easy use (18" is the minimum). The longer the tubing, the more attenuated the heart sounds. In theory, double tubing is superior to single tubing in transmitting sounds accurately, especially at higher frequencies. In practice, both single tubing (Littmann-type) and double tubing (Rappaport-Sprague type) models seem to work well. The chest piece should have two sides – The Diaphragm and the Bell. The diaphragm tends to attenuate lower frequencies and accentuate higher frequencies. This is important for routine use since the lower frequency sounds are often the most intense and can mask the more important and diagnostic higher frequency sounds. The bell tends to attenuate higher frequencies and accentuate lower frequencies and is quite useful in detecting certain low frequency, low intensity sounds. The bell is particularly helpful in large animals. A quiet environment is essential for proper auscultation. Even mild background noise can obscure normal and abnormal heart sounds. Technique of Auscultation The first step in a systematic approach to cardiac auscultation is palpation of the thorax and determining the location and intensity of the apex beat (cardiac impulse, apical thrust). This region is sometimes referred to as the point of maximal intensity (PMI) in the normal animal. The presence and location of any palpable thrills should be noted. Displacement of the apical beat in any direction may be due to conditions that alter the position of the heart within the thoracic cavity (intrathoracic neoplasm, hernia, effusions, cardiomegaly). It may also be reduced in intensity or absent with severe heart disease or with severe pericardial or pleural effusion. In addition, the location of the PMI is used as the initial landmark to begin auscultation. 2 VPP 3215 Veterinary Structure and Function I Practical Manual Auscultation should be systematic and involves listening to all areas of the heart (inching) using the diaphragm then repeating the same sequence with the bell of the stethoscope. Another method alternates the diaphragm and the bell at each location until all areas of the heart are covered. The veterinarian should concentrate on each phase of the cardiac cycle and listen for specific cardiac events. This should include normal heart sounds, systolic and diastolic transient sounds, and systolic, diastolic, and continuous murmurs at each location. Once the left hemithorax is completed, the same technique is repeated on the right hemithorax. In most cases, the PMI of the normal heart is over the mitral area or left apex. Other areas employed as designations for auscultation include the tricuspid (right apex), aortic, and pulmonic positions (left base). At the left cardiac apex the first heart sound, S1, is usually louder then the second heart sound, S2. These two sounds are landmarks and are used to reference systole and diastole. Difficulties in identifying them may arise if the heart rate is irregular or rapid, if the sounds are faint, or if several abnormal cardiac events occur simultaneously. Inaccurate identification of S1 and S2 will confuse even the best attempts to characterize systole, diastole, and the various transient sounds and murmurs. Fortunately, a very simple technique exists to help identify systole and diastole in questionable cases. By palpating the arterial pulse while listening at the PMI with the diaphragm of the stethoscope, the first heart sound will precede and the second heart sound will follow the rise of the arterial pulse. HEART SOUNDS Heart Sounds Sound Origin/sources PMI Quality early ventricular contraction, abrupt deceleration of blood associated with tensing of loud, high the A-V valve leaflets and A-V valve closure, frequency, longer, S1 L apex opening of the semi-lunar valves and vibrations louder, lower associated with ejection of blood into the great pitch than S2 vessels loud, high closure of the semilunar valves, abrupt frequency, S2 deceleration of blood in the great vessels, L base sharper, shorter, opening of the A-V valves higher pitch than S1 rapid deceleration of blood in the ventricles at soft, low S3 the end of the rapid ventricular filling phase, L apex frequency, lower transient A-V valve closure may occur pitch than S2 vibrations associated with blood flow from atria soft, low S4 to ventricle during atrial contraction, transient L base frequency, lower A-V valve closure may occur pitch than S1 3 VPP 3215 Veterinary Structure and Function I Practical Manual Transient Sounds Once S1 and S2 have been properly identified, the examiner must systematically auscult the patient for transient sounds including normal heart sounds. The first heart sound is lower in frequency and longer in duration than the second sound and is heard best in the mitral and tricuspid valve areas. Occasionally, the first sound may be split into two components. This can be normal; however, it can also result from asynchronous closure of the A-V valves and may be attributed to electrical factors (bundle branch blocks, ectopic beats, or artificial pacing), mechanical factors (mitral or tricuspid stenosis), or a combination of events. A split first heart sound must be differentiated from an S4-S1 and S1-systolic click. The second heart sound is heard best as the stethoscope is gradually inched to the heart base at the aortic area (left 4th ICS at the point of the shoulder) and in the lower left third ICS at the pulmonic area. S2 is usually louder in these areas than S1. The second heart sound is higher in frequency and shorter in duration than the first sound. In small animals, aortic valve closure (A2) precedes pulmonic valve closure (P2) by a short interval which is usually not detectable by the ear; therefore, S2 is heard as a single sound. In many normal horses and during inspiration in normal large dogs, audible splitting of the second heart sound may occur. Respiratory conditions with airway obstruction resulting in exaggerated respiratory effort and large fluctuations in intrapleural pressure may augment physiologic splitting. In horses, A2 may normally follow P2 and cause splitting of S2 which is accentuated on expiration. 4 VPP 3215 Veterinary Structure and Function I Practical Manual Systolic sounds: Besides the two basic heart sounds, other intermittent transient sounds may occur and must be identified. The examination commences at the left apex during the systolic interval in order to appreciate ejection sounds and systolic clicks, both of which are high frequency sounds of short duration heard best with the diaphragm. Systolic clicks are short mid to high frequency sounds which can occur in early, mid or late systole. They are heard best over the mitral and/or tricuspid valve and may be variable in occurrence, position, and intensity. They occur most commonly in dogs in association with systolic murmurs of mitral or tricuspid regurgitation but can otherwise occur in normal dogs. In humans, most systolic clicks are associated with prolapse of one of the A-V valve leaflets during systole. The origin of this sound in dogs is as yet uncertain but may be related to the mitral chordae tendineae. Systolic clicks may be confused with split first or second sounds or with gallop sounds. They can be differentiated by recalling they are high frequency sounds, can be labile, occur during systole and are best heard over the mitral or tricuspid valves. Diastolic sounds: The examiner must listen to the diastolic interval for a third or fourth heart sound. The process begins at the left apex using the diaphragm and bell and slowly moving toward the left base, concentrating on the diastolic interval. The third and fourth heart sounds are low frequency sounds and heard best with the bell of the stethoscope. Third heart sounds are low pitched sounds best heard at the cardiac apex and is associated with rapid ventricular filling. It is best detected with the bell of the stethoscope and should be differentiated from an S4 (at times this is difficult) and split second heart sounds. At slower heart rates, S3 occurs in early diastole and is frequently heard shortly after S2. Split second heart sounds are high frequency and more prominent at the heart base. An S3 is normal in horses and cattle, but is pathological in the dog and cat. Prominent S3 sounds are commonly referred to as gallop rhythms due to the presence of three distinct heart sounds (S1, S2, and S3 or S4). S3 gallops frequently accompany congestive heart failure and ventricular dilatation in dogs with advanced mitral insufficiency and in dogs and cats with congestive dilated cardiomyopathy. Fourth heart sounds occur at the beginning of atrial systole. In the normal dog and cat, no third or fourth heart sound is auscultated. However, if present, S4 is low in frequency and is best appreciated at the cardiac apex. It occurs shortly before S1. It is best detected with the bell of the stethoscope and should be differentiated from an S3 and split first heart sound. A split first heart sound is of higher frequency and the two components sound identical. Gallops occur when there is altered compliance of either ventricle, as seen in feline hypertrophic cardiomyopathy, semilunar valve stenosis or hypertension. Fusion of S3 and S4 (summation gallop) may occur at rapid heart rates. This results in a marked triple or quadruple rhythm heard best with the bell at the left apex. This frequently occurs in cats or dogs with advanced heart disease and tachycardias. Third and fourth heart sounds usually diminish in intensity as you move toward the base of the heart or use the diaphragm of the stethoscope. 5 VPP 3215 Veterinary Structure and Function I Practical Manual Other diastolic sounds include pericardial friction rubs. These rubs are creaking or scratching sounds heard in systole or either systole and diastole and may be mistaken for a short murmur or other transient sounds. They are usually associated with pericarditis (especially acute or fibrinous) with minimal fluid accumulation. It is heard most commonly in cows with traumatic reticulopericarditis, along with splashing or tinkling sounds when both fluid and gas are present in the pericardial sac. Group work Try to perform the following procedures : 1.Determine the pulse rate (at the level of the facial or mandibular artery-horse/large animals, femoral in dogs, cats and small ruminants) 2.Determine the heart rate of the animal. Identify S1 and S2, not how many S1 and S2 per minute. 3.Determine the number of heart sounds that is audible to you and your group mates (S1, S2, S3. 4.Determine the number of PMI’s audible to you and your group mates. 5.Are the heart sounds and heart rates normal ? Do you think you have heard any abnormal heart sounds ? 6 VPP 3215 Veterinary Structure and Function I Practical Manual Cardiac Murmurs (OPTIONAL  ) Murmurs are groups of sounds of longer duration than transient heart sounds. They generally arise from turbulent blood flow (vibrations) when the normally smooth, quiet laminar flow is disrupted by alterations in blood viscosity, vessel diameter, or abnormal flow patterns from insufficient valves or abnormal communications between cardiac chambers. Several characteristics are important in describing murmurs. These include: 1) intensity, 2) frequency (pitch), 3) shape, 4) quality, 5) time of occurrence and duration in the cardiac cycle, and 6) location. 1. Intensity Grade l murmurs are the softest audible murmur which can only be heard by special effort. Grade ll murmurs are faint and clearly heard after a few seconds of auscultation. Grade III murmurs are heard immediately and of moderate intensity. Grade IV murmurs are loud but do not produce a palpable thrill. Grade V murmurs are loud and produce a palpable thrill. Grade Vl murmurs are very loud and produce a thrill. The murmur can be heard with the chest piece slightly removed from the chest wall. 2. Frequency Murmurs may be described as high, medium or low pitched or of mixed frequency. 3. Shape Murmurs may be described in terms of their shape: band-shaped, crescendo decrescendo (diamond shaped), decrescendo, or plateau (regurgitant) based on the variations in intensity during the cardiac cycle. 4. Quality Refers to the arrangement of frequency components producing a subjective impression described in such terms as harsh, blowing or musical. 5. Time of occurrence and duration Murmurs can be divided into systolic, diastolic or continuous types based on the timing during the cardiac cycle. Their location and duration within systole are further modified by terms such as holosystolic, early systolic, mid systolic (ejection murmur), or late systolic, and within diastole as early, mid, late and holodiastolic. 6. Location The position on the thorax where the murmur is best heard is called the point of maximum intensity (PMI). Specific location of the PMI can be related to the four valve areas, by intercostal space, or simply at the heart base or apex. The art and science of cardiac auscultation develops slowly. One cannot expect to detect every abnormal heart sound particularly in animals where the heart rate is fast. Auscultation requires a consistent, systematic approach and verification through practice and consultation with others. With practice, a technique can be developed that will lead to accurate auscultatory interpretation and more intelligent selection of diagnostic tests and therapeutic plans. 7