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Until recently the inclusion of heart tone auscultation  was not considered to be important or fundamental to paramedic education, and as a result any description of heart tones beyond "they should sound like lub-dub" was not a common occurrence.   However with the ever expanding scope of paramedic practice and the implementation of the 1998 DOT National Standard Cirriculum, the ability to auscultate and interpret normal and abnormal heart tones is a skill that is required daily of pre-hospital care professionals.  This page will introduce both normal and abnormal heart tones, their pathophysiology, selected disease processes that may cause abnormal findings, and techniques for their inclusion in your cardiac examination.

The Cardiac Cycle
The first step in understanding heart tones is understanding the normal pathophysiology that causes them.  Heart tones are caused by the closure of the valves of the heart, while valve opening is normally a silent event.  The heart contracts and relaxes rhythmically to ensure proper circulation, a process that creates two distinct phases in the cardiac cycle.  During systole ventricular contraction raises the pressure in the ventricles and forces the mitral (bicuspid) and tricuspid valves closed.   It is the closure of these valves that cause the S₁ heart tone.  As the pressure in the ventricles increases blood is ejected from the right ventricle through the pulmonic valve into the pulmonary artery, and from the left ventricle through the aortic valve into the aorta.  (The pulmonic and aortic valve are collectively referred to as the semilunar valves)  When the ventricles are nearly empty the pressure in the ventricles fall below the pressure in the aorta and pulmonary artery allowing the semilunar valves to close.  It is the closure of these valves that cause the S₂ heart tone.  As ventricular pressure continues to fall below atrial pressure, and diastole begins, the mitral and tricuspid valves open allowing the blood collected in the atria to flow into the ventricles.  Diastole is a relatively passive process as blood flows from the atria into the ventricles.  This accounts for approximately 70% of ventricular volume.  When ventricular filling is almost complete when the atria will contract ejecting approximately 20% more blood into the ventricles.   This is often referred to as "atrial kick" and contributes significantly to stroke volume.  The cycle the repeats itself with the beginning of systole as the ventricles contract causing closure of the mitral and tricuspid valve.  During the cardiac cycle there can be several normal and abnormal presentations of the S₁/S₂ heart tones.  Dependent upon the patients past medical history there can also be several other tones present during the cardiac cycle.  Further discussion of these normal and abnormal tones, their causes, and examples, will be presented later.

Auscultation in the Emergency Setting
Although complete evaluation of heart tones requires examining the patient in several anatomic positions in a quiet environment, this is not always possible in the emergency setting.  Therefore some modifications are needed to perform this evaluation in the pre-hospital setting in order to obtain an adequate gross assessment of heart tones.  The first issue to address in the pre-hospital setting is ambient noise.  Because the human heart tones are of relatively low frequency and in a range that is somewhat difficult for the human ear to detect, the best place to perform this assessment is while on scene in as quiet an environment as possible. (as long as the situation allows for this)  The second issue is patient position.  Evaluating the pt while supine or semi-fowlers while providing respiratory instruction will suffice for the pre-hospital evaluation, and evaluation of the patient in the left lateral recumbent position, or sitting up and leaning forward can be omitted.  Because shivering, movement, and clothing  increase adventitious sounds, and because comfort is important, make certain the patient is warm and relaxed before beginning the evaluation when possible.  Nevertheless a comfortably warm stethoscope should be placed on the exposed chest or under the patients clothing.

It is a common mistake to try to hear all of the sounds in the cardiac cycle at one time.  Take the time to isolate each sound and each pause in the cycle, listening separately and selectively for as many beats as necessary to evaluate the sounds.  It takes time to "tune in", so you should not rush.  In the emergency setting it is acceptable to listen in four areas to isolate each of the valves, as depicted in the picture below.
As you can see the areas in which you will auscultate do not lie directly over the valves themselves.  This is because sound is transmitted in the direction of blood flow, specific heart tones are best heard over areas where blood flows after it passes through a valve.  Assess first with the diaphragm using firm pressure, and then with the bell using light pressure.  Ausclutation should be performed in the following areas

Aortic Valve        Second R intercostal space @ R sternal border
Pulmonic Valve    Second L intercostal space @ L sternal border
Tricuspid Valve    Fourth L intercostal space @ L sternal border
Mitral Valve         Fifth L intercostal space @ mid clavicular line

As you auscultate heart tones there are specific things you want to note.   Also it is important to remember that your areas of auscultation will change if the heart is not in the left mediastinum.  In situs inversus the heart, and spleen are on the right and the liver is on the left.  In dextracardia the heart alone is rotated, but remains in the left mediastinum.  In these situations adjust to the anatomic alteration by visualizing a mirror image of the above picture.  As you auscultate each of the above areas, pause and listen selectively for each phase of the cardiac cycle and note the following:

• Are the tones clear or muffled and/or distant
• Assess the overall rhythm and rate of the heart
• Concentrate on systole listening for any extra sounds or murmurs.   (S₁ marks the beginning of systole)
• Concentrate on diastole, which is a longer interval than systole,  listen for any extra sounds or murmurs.
• Instruct the pt to hold his breath during expiration and listen for S1.   Note the intensity, any variation, or splitting of S₁
• Instruct the pt to breathe normally and listen closely for any splitting of S₂ during inspiration

Basic Heart Tones

• S1/S2 (Normal)
• Split S1
• Split S2
• Split S1 and S2
• S3 Gallop
• S4 Gallop
• Quadruple Gallop
• Summation Gallop

Murmurs

• Pathophysiology
• Systolic Murmur
• Diastolic Murmur
• Mitral Valve Prolapse

Extra (Adventitious) Heart Tones

• Mid Systolic Click
• Diastolic Rumble
• Opening Snap
• Atrial Septal Defect
• Patent Ductus Arteriosus
• Mitral Stenosis
• Ejection Click
• Ventricular Septal Defect

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