Thursday, March 3, 2011

Cardiology: Murmurs!

The stethoscope has practically become the icon of healthcare.  To wear a stethoscope suggests that a person has some sort of clinical knowledge.  After all, why else would a person have a stethoscope on their person if they did not actually know how to use it?  A stethoscope amplifies sound to make very subtle noises audible to the human ear.  Thus the sounds of the hearts valves closing, the movement of air into and out of the lungs, the bowels doing their thing, and so on get recognized clinically with the use of a stethoscope.  Without an understanding of what the sounds actually mean such information proves useless, allowing the stethoscope to serve as nothing more than a mere piece of jewelry.

When putting the stethoscope to the chest one can look at the chest as having four separate areas in which to listen for heart sounds:
  • Aortic: the right second intercostal space adjacent the sternum
  • Pulmonic: the left second intercostal space adjacent the sternum
  • Tricuspid: the left third and fourth intercostal spaces adjacent the sternum
  • Mitral: the left fifth intercostal space in the mid-clavicular line, often the point of maximal intensity
The location of a heart sound allows for the listener to determine the significance of a murmur based on the clinical picture.  Some of the sickest patients may have a murmur which needn't be addressed while some of the healthiest patients can have murmurs which signify the presence of a silent killer.   This means that the clinician wields a heavy tool in his or her stethoscope.  

Just as a jugular venous pressure wave shows the cardiac cycle of systole and diastole, the stethoscope auscultation, or listening to the heart provides an audible representation of heart function.  Normally two sounds, or beats get heard: S1 and S2.  When someone describes the heart as making a lub dub noise, they are referring to S1 and S2.
  • S1 is the sound of the bicuspid and tricuspid valves closing during systole, the aortic and pulmonic valves should be open
  • S2 is the sound of the aortic and pulmonic valves closing during diastole, the mitral and tricuspid valves should be open
To learn mumurs, which usually sound like a whoosh instead of or after a beat, it's easiest to think of them in terms of whether they occur in systole or diastole.  Knowing their location helps to limit the differential.

Systolic murmurs are those which occur during systole, and can be further classified upon when the murmur actually occurs.

  • Early to mid systolic murmurs
    • Pulmonic Stenosis (PS)
    • Tricuspid Regurgitation (TR)
    • Atrial Septal Defect (ASD)
    • Idiopathic Hypertrophic Subaortic Stenosis (IHSS)
    • Mitral Regurgitation (MR)
  • Mid to late systolic murmurs
    • Mitral Valve Prolapse (MVP)
    • Aortic Stenosis (AS)
  • Holocystolic--occurring throughout all of systole
    • Tricuspid Regurgitation (TR)
    • Mitral Regurgitation (MR)
    • Ventricular Septal Defect (VSD)
Notice that TR and MR can occur as either early/mid systolic as well as pan-systolic.  The difference being that something acute occurs early, where as a chronic condition happens throughout.  

Diastolic murmurs also occur, albeit considerably less to know than the list of 10 systolic murmurs.  Often one auscultates these best in the neck, and can quantify them based on the sound they make: a rumble vs. a blow.
  • Diastolic Rumbles
    • Tricuspid Stenosis (TS)
    • Mitral Stenosis (MS)
    • Austin Flint 
  • Diastolic Blows
    • Aortic Regurgitation (AR)
    • Pulmonic Regurgitation (MR)
Once the clinician has auscultated a murmur he or she must somehow differentiate the type.  An echocardiogram can effectively diagnose problems with valves and septa (the plural for septum, not the transit authority).  However, since not always practical or available, the practitioner should remember a few fundamentals to accurately diagnose a murmur by physical exam.  Since the heart handles systemic circulation, look at the heart as a dual circuit: the right side of the heart receives blood from the venous circulation, anything which increases venous return will increase a murmur on the right; the left side of the heart pumps blood into arterial circulation, anything which increases the arterial blood pressure will increase a left sided murmur.  
  • Inspiration & leg raising: increase the amount of blood from venous circulation returning to the heart, this increase in preload leads to an increase in the duration of right sided murmurs
  • Squatting: increases the amount of blood returning to the heart as well as the systemic arterial blood pressure, this increase in both preload and afterload results in increased duration of right and left sided murmurs
  • Hand grip: constriction of the radial and ulnar arteries leads to a backup of arterial blood which increases the arterial blood pressure, this increase in afterload causes an increase in left sided murmurs
  • Valsalva & standing: leads to a decrease in both preload and afterload, ultimately reducing the duration of both right sided and left sided murmurs
One very important exception exists to these rules: IHSS
  • Duration increases with valsalva
  • Duration decreases with squatting
In considering the pathophysiology of IHSS, it makes sense.  Because of the hypertrophy of the subaortic area of the left ventricle blood will have a difficult time getting from the left ventricle into the aorta.  However, if the pressure in the arterial circulation increases it will lead to an increase in left ventricular pressure in order to compensate.  Where as this will increase the effect of most left-sided pathologies and thus increase their associated murmurs, in IHSS the pressure increase will push against the hypertrohpied tissue and essentially push it out of the way such that blood will move by easier and result in a diminished murmur.  Following the same logic the opposite is also true.  

Some people could not help themselves and insisted on putting their namesake to a diastolic murmur.  Nonetheless three particularly important ones exist:
  • Carey Coombs Murmur: the diastolic murmur of mitral stenosis heard as a result of rheumatic heart disease
  • Graham Steell Murmur: the diastolic murmur of pulmonic valve regurgitation
  • Austin Flint Murmur: the diastolic murmur heard best in the mitral area associated with severe aortic regurgitation compressing against a normal mitral valve

Although not very recent, a 1990 study showed that in diagnosing pediatric murmurs the clinical skills of an experienced cardiologist have a sensitivity of 96% and specificity of 95%.  While it may seem great, just ask yourself this: how many doctors today rely on their physical exam skills as much as those who practiced decades ago?  Just how many doctors today actually qualify as experienced as determined by that article?  Since the article left out such criteria I cannot know, but I suspect the number would be considerably less. 


ResearchBlogging.org

John F. Smythe MD, Otto H. P. Teixeira MD, Peter Vlad MD, Pierre Paul Demers MD, & William Feldman MD (1991). Initial evaluation of heart murmurs: Are laboratory tests necessary? The Indian Journal of Pediatrics, 58 (2), 231-231 DOI: 10.1007/BF02751126

1 comment:

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