Explanation of Auscultatory findings to follow.
The presence of pulse deficits should alert the diagnostician to the occurrence of premature ectopic beats. These may be either supraventricular or ventricular in origin, only the ECG can distinguish these.
A positive test result indicates that there is elevated pressure in the right atrium or right ventricle. If one were to classify an elevated pressure in the right heart as mild, moderate or severe, venous distention at rest indicates a severe elevation in pressure, whereas a positive HJR indicates a moderate elevation in pressure. Patients with a mild elevation in pressure to the right heart cannot be identified on physical examination.
The palpable strength of the pulse is determined by:
The arterial pulse (through the effect of systolic and diastolic pressure) is affected by:
Comment: The arterial pulse can be maintained near normal in the face of a reduced cardiac output, mainly due to the effect of the compensatory arterial vasoconstrictor mechanisms.
The goals of auscultation are:
Bradycardia, normal, or tachycardia
To be distinguished from a respiratory arrhythmia
Occur due to insulation between sound source and stethoscope as in:
- Presence of fluid in the pericardial space = pericardial effusion
- Presence of fluid in the pleural space = pleural effusion
- Mass in the pleural space or pericardial space
- Pleural tumors
- Pericardial tumors
- Diaphragmatic hernia either to the pleural or pericardial space
- Lung parenchymal disease
May be a normal variant in some dogs
Heart murmurs Gallop sounds: S3 or S4 or summation Systolic clicks Split heart sounds: S1 or S2 Pericardial friction rubs - rare in small animals
Other than for detecting asystole, auscultation cannot provide definitive evidence of heart failure. Rarely, individuals may have heart failure in the face of normal heart sounds and cardiac rhythm. The finding of gallop sounds is often very strong evidence of severe myocardial dysfunction. The presence of a murmur does not equate with heart failure. In fact, most patients with a heart murmur do not have heart failure.
To hear examples of normal and abnormal heart sounds, see Heart Sounds of the Month
2. For the best sound reproduction, consider the following:
3. Only auscult a patient when in the standing or sitting position. Auscultation of the patient in lateral or dorsal recumbency can result in creating false murmur like sounds (perhaps rubbing sounds) and/or impairs our ability to localize the PMI for a "real" murmur.
Reynolds number defines the variables that promote disturbed (non laminar) flow in a vessel or chamber. When Reynolds Number exceeds a critical value flow becomes turbulent.
Reynolds No = (Area)(Velocity)(Density) / Viscosity
Area = cross-sectional area of the chamber, orifice, or vessel; Velocity = velocity of blood flow (note that this is related to the area); Density = density of blood; Viscosity = viscosity of blood (affected mainly by the red blood cell count and protein count)
Blood flow turbulence can be created by high-velocity flow, flow from a narrow region into a larger area, or low blood viscosity.
Anything that muffles the heart sounds can obscure a murmur such as obesity, thoracic effusions, or loud respiratory sounds.
It is my belief that similar innocent heart murmurs may also occur in the adult, particularly of large and giant breed dogs.
Functional (physiologic) murmurs may also occur:
These are important features to distinguish innocent murmurs from congenital heart murmurs.
These "other features" are clearly of secondary use and less sensitive than the primary features of timing and PMI.
The PMI refers to the location where the murmur is loudest.The left chest wall is typically divided with respect to PMI into two positions.
- left heart base (includes both the pulmonic valve and aortic valve areas, and discriminating between these two is often problematic)
- left heart apex (mitral valve area)
The right chest wall is typically divided with respect to PMI into two positions.
mid heart (tricuspid valve area) sternal border (typical of a VSD)
Timing of murmurs, at the PMI, is generally divided into one of three classes:
systolic (occurring during systole) diastolic (occurring during diastole) continuous (present at all times)
- The very vast majority of murmurs are systolic
- When soft they are usually early in systole and disturb the end of S1. S1 often appears slurred in these cases as opposed to ending abruptly as is normally the case.
- The careful clinician focuses on the end of S1 for soft systolic murmurs.
- Holosystolic murmur: refers to a systolic murmur that begins during or immediately after S1 and ends with the onset of S2
- Pansystolic murmur: refers to a systolic murmur that begins during or immediately after S1 and continues into and obscures S2 (note that left ventricular pressure continues to be greater than left atrial pressure after aortic valve closure - during isovolumetric relaxation).
Systolic Murmur Examples:
- Very rare
- Low frequency
- Rather low intensity and so are graded out of 4, not 6
- Best identified with the bell of the stethoscope
- Common, but less so than systolic
- Typically associated with a PDA, but also arteriovenous fistulas
- Usually vary in intensity throughout the cardiac cycle, however the murmur is detected at all times
- The continuous nature of the murmur may only be noted at the PMI, while at other locations it may only be systolic, for example.
Continuous Murmur Examples:
To and Fro murmurs:
- The name for the situation when a systolic murmur and a diastolic murmur (due to different physiologic etiologies) coexist.
To and fro Murmur Example:
Using the timing and PMI of a murmur, the following algorithm may be used to arrive at a presumptive diagnosis:
Recall causes for a continuous murmur: PDA or Arteriovenous Fistula
The intensity of the murmur at its origin is related to (Blood flow velocity) x (Rate of flow). Overall, the intensity of a heart murmur is not related to the severity of the lesion; however for some diseases there is a rough correlation between the intensity of the murmur and the severity of the lesion such as:
- Mitral valve insufficiency
- Aortic / subaortic valve stenosis
- Pulmonic valve stenosis
The intensity of a murmur is graded on a scale of 1 to 6:
Grade 1 = a very soft, localized murmur detected only after several minutes of listening. Grade 2 = a soft murmur, heard immediately but localized to a small area. Grade 3 = a moderately intense murmur that is readily detected and detected over more than one location. Grade 4 = a moderately intense or loud murmur, detected over several areas, usually both sides of the chest, however a precordial thrill is not detected in this case. Grade 5 = a loud murmur accompanied by a precordial thrill over the point of maximal intensity. Grade 6 = a very loud murmur accompanied by a precordial thrill and the murmur is detected when the stethoscope is pulled slightly off the chest wall.
S3 gallop (ventricular gallop)
- Low frequency sound
- Occurs shortly after the S2 sound, at the beginning of diastole, during the rapid filling phase.
- Called a ventricular gallop
- Not normal in dogs and cats. Indicates ventricular failure. May be an early finding and the only auscultatory evidence of heart failure.
- Indicates diastolic dysfunction
- Associated with reduced compliance of the ventricle while filling under conditions of high filling pressures (stiffer ventricle).
- Caused by the sudden termination of longitudinal expansion of the ventricular wall during brisk early diastolic filling during the period of rapid ventricular filling.
- Indicates severe myocardial disease
S4 gallop (atrial gallop)
- Low frequency sound
- Occurs shortly before the S1 sound, at the end of diastole, during atrial contraction.
- Called an atrial gallop
- Not normal in dogs and cats. Usually indicates ventricular failure. May be the only auscultatory evidence of heart failure.
- Indicates diastolic dysfunction
- Associated with the atria trying to force blood into an already over-distended ventricle or because the atria are forcing blood into a stiff ventricle. Atrial contraction is required for an audible S4 sound. Thus it does not occur in atrial fibrillation.
- Occurs in disorders with impaired relaxation of the ventricle typical of disorders of concentric hypertrophy
- May be a normal finding in older stressed cats
- At fast heart rates an S3 and S4 gallop will superimpose to cause one sound called a summation gallop.