Hypertrophic cardiomyopathy outflow obstruction: Difference between revisions

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==Systolic Anterior Motion of the Mitral Valve (SAM)==
==Systolic Anterior Motion of the Mitral Valve (SAM)==
If dynamic outflow obstruction is present in a patient with HCM, it is usually due to systolic anterior motion (SAM) of the anterior leaflet of the [[mitral valve]]. Systolic anterior motion of the mitral valve (SAM) may be due a subaortic bulge of the septum along with narrowing the left ventricular outflow tract, which taken together cause high velocity flow. This in turn is associated with the Venturi effect which is a local low pressure zone in the left ventricular outflow tract. This low pressure zone was thought to suck the [[mitral valve]] anteriorly into the septum. More recently, however, SAM onset has been observed to be instead a low velocity phenomenon. <ref name="Jiang, Levine et al 1987">Jiang L, Levine RA, King ME, Weyman AE. An integrated mechanism for systolic anterior motion of the mitral valve in hypertrophic cardiomyopathy based on echocardiographic observations. ''Am Heart J'' 1987; '''113''':633–44</ref> <ref name="Sherrid, Gunsburg et al 2000">Sherrid MV, Gunsburg DZ, Moldenhauer S, Pearle G. Systolic anterior motion begins at low left ventricular outflow tract velocity in obstructive hypertrophic cardiomyopathy. ''[[Journal of the American College of Cardiology|J Am Coll Cardiol]]'' 2000; '''36''':1344–54</ref>. The role of Venturi forces in the left ventricular outflow tract may be less important than previously thought.
If dynamic outflow obstruction is present in a patient with HCM, it is usually due to systolic anterior motion (SAM) of the anterior leaflet of the [[mitral valve]]. Systolic anterior motion of the mitral valve (SAM) may be due a subaortic bulge of the septum along with narrowing the left ventricular outflow tract, which taken together cause high velocity flow. This in turn is associated with the Venturi effect which is a local low pressure zone in the left ventricular outflow tract. This low pressure zone was thought to suck the [[mitral valve]] anteriorly into the septum. More recently, however, SAM onset has been observed to be instead a low velocity phenomenon. <ref name="Jiang, Levine et al 1987">Jiang L, Levine RA, King ME, Weyman AE. An integrated mechanism for systolic anterior motion of the mitral valve in hypertrophic cardiomyopathy based on echocardiographic observations. ''Am Heart J'' 1987; '''113''':633–44</ref> <ref name="Sherrid, Gunsburg et al 2000">Sherrid MV, Gunsburg DZ, Moldenhauer S, Pearle G. Systolic anterior motion begins at low left ventricular outflow tract velocity in obstructive hypertrophic cardiomyopathy. ''[[Journal of the American College of Cardiology|J Am Coll Cardiol]]'' 2000; '''36''':1344–54</ref>. The role of Venturi forces in the left ventricular outflow tract may be less important than previously thought.
While the Venturi effect was thought to cause the abnormality in prior studies, more recent echocardiographic studies indicates that drag, which is more of a pushing force rather than a sucking force like the Venturi effect, may be the dominant hydrodynamic force acting on the mitral leaflets
<ref name="Jiang, Levine et al 1987"/><ref name="Sherrid, Gunsburg et al 2000"/><ref name="Sherrid, Chu et al 1993">Sherrid MV, Chu Ck, DeLia E, Mogtader A, Dwyer Jr. EM, An echocardiographic study of the fluid mechanics of obstruction in hypertrophic cardiomyopathy. ''[[Journal of the American College of Cardiology|J Am Coll Cardiol]]'' 1993; '''22''':816–25</ref><ref name="Levine, Vlahakes et al 1995">Levine RA, Vlahakes GJ, Lefebvre X, et al. Papillary muscle displacement causes systolic anterior motion of the mitral valve. ''[[Circulation (journal)|Circulation]]'' 1995; '''91''':1189–95</ref><ref name="Messmer 1994">Messmer BJ. Extended myectomy for hypertrophic obstructive cardiomyopathy. ''Ann Thorac Surg'' 1994; '''58''':575–7</ref>
<ref name="Schoendube, Klues et al 1995">Schoendube FA, Klues HG, Reith S, Flachskampf FA, Hanrath P, Messmer BJ. Long-term clinical and echocardiographic follow-up after surgical correction of hypertrophic obstructive cardiomyopathy with extended myectomy and reconstruction of the subvalvular mitral apparatus. ''[[Circulation (journal)|Circulation]]'' 1995; '''92''':II-122–7</ref>.
 
The videos below show examples of systolic anterior motion of the mitral valve:


<youtube v=Y7JUVTXHBs0/>
<youtube v=Y7JUVTXHBs0/>
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<youtube v=6TWb-wIL0H0/>
<youtube v=6TWb-wIL0H0/>


While the Venturi effect was thought to cause the abnormality in prior studies, more recent echocardiographic studies indicates that drag, which is more of a pushing force rather than a sucking force like the Venturi effect, may be the dominant hydrodynamic force acting on the mitral leaflets
==Impact of Systolic Anterior Motion of the Mitral Valve: The Spike and Dome Pattern to the Carotid Pulse==
<ref name="Jiang, Levine et al 1987"/><ref name="Sherrid, Gunsburg et al 2000"/><ref name="Sherrid, Chu et al 1993">Sherrid MV, Chu Ck, DeLia E, Mogtader A, Dwyer Jr. EM, An echocardiographic study of the fluid mechanics of obstruction in hypertrophic cardiomyopathy. ''[[Journal of the American College of Cardiology|J Am Coll Cardiol]]'' 1993; '''22''':816–25</ref><ref name="Levine, Vlahakes et al 1995">Levine RA, Vlahakes GJ, Lefebvre X, et al. Papillary muscle displacement causes systolic anterior motion of the mitral valve. ''[[Circulation (journal)|Circulation]]'' 1995; '''91''':1189–95</ref><ref name="Messmer 1994">Messmer BJ. Extended myectomy for hypertrophic obstructive cardiomyopathy. ''Ann Thorac Surg'' 1994; '''58''':575–7</ref>
Because the mitral valve leaflet doesn't get pulled into the left ventricular outflow tract (LVOT) until after the [[aortic valve]] opens, the initial upstroke of the arterial pulse pressure will be normal. When the mitral valve leaflet gets pushed into the LVOT, the arterial pulse will momentarily collapse and will later be followed by a second rise in the pulse pressure, as the left ventricular pressure overcomes the increased obstruction caused by the SAM of the mitral valve. This can be seen on the physical examination as a double tap upon palpation of the apical impulse and as a double pulsation upon palpation of the carotid pulse, known as ''[[pulsus bisferiens]]'' or a "[[spike and dome pattern]]" to the carotid pulse.
<ref name="Schoendube, Klues et al 1995">Schoendube FA, Klues HG, Reith S, Flachskampf FA, Hanrath P, Messmer BJ. Long-term clinical and echocardiographic follow-up after surgical correction of hypertrophic obstructive cardiomyopathy with extended myectomy and reconstruction of the subvalvular mitral apparatus. ''[[Circulation (journal)|Circulation]]'' 1995; '''92''':II-122–7</ref>.
In obstructive HCM the mitral leaflets are often large
<ref name="Klues, Maron et al 1992">Klues HG, Maron BJ, Dollar AL, Roberts WC. Diverstiy of structural mitral valve alterations in hypertrophic cardiomyopathy. ''[[Circulation (journal)|Circulation]]'' 1992; '''85''':1651–60</ref>
and are anteriorly positioned in the LV cavity
<ref name="Jiang, Levine et al 1987"/>
<ref name="Henry, Clark et al 1975">Henry WL, Clark CE, Griffith JM, Epstein SE. Mechanism of left ventricular outflow obstruction in patients with obstructive asymmetric septal hypertrophy (idiopathic hypertrophic subaortic stenosis). ''Am J Cardiol'' 1975; '''35''':337–45</ref>
due to anteriorly positioned papillary muscles<ref name="Jiang, Levine et al 1987"/> that at surgery are often "agglutinated" onto the LV anterior wall by abnormal attachments
<ref name="Messmer 1994"/>
<ref name="Schoendube, Klues et al 1995"/>.
 
The mid-septal bulge aggravates the malposition of the valve and redirects outflow so that it comes from a lateral and posterior direction<ref name="Sherrid, Chu et al 1993"/>. The abnormally directed outflow may be visualized behind and lateral to the enlarged mitral valve, where it catches it, and pushes it into the septum <ref name="Jiang, Levine et al 1987"/>
<ref name="Sherrid, Gunsburg et al 2000"/>
<ref name="Sherrid, Chu et al 1993"/>
<ref name="Levine, Vlahakes et al 1995"/>.
There is a crucial overlap between the inflow and outflow portions of the left ventricle
<ref name="Schwammenthal and Levine 1996">Schwammenthal E, Levine RA. Dynamic subaortic obstruction: a disease of the mitral valve suitable for surgical repair? ''[[Journal of the American College of Cardiology|J Am Coll Cardiol]]'' 1996; '''28''':203–6</ref>.
As SAM progresses in early systole the angle between outflow and the protruding mitral leaflet increases. A greater surface area of the leaflets is now exposed to drag which amplifies the force on the leaflets – drag increases with increasing angle relative to flow<ref name="Sherrid, Chu et al 1993"/>. An analogy is an open door in a drafty corridor: the door starts by moving slowly and then accelerates as it presents a greater surface area to the wind and finally it slams shut. The necessary conditions that predispose to SAM are: anterior position of the mitral valve in the LV, altered LV geometry that allows flow to strike the mitral valve from behind, and chordal slack
<ref name="Jiang, Levine et al 1987"/>
<ref name="Sherrid, Gunsburg et al 2000"/>
<ref name="Sherrid, Chu et al 1993"/>
<ref name="Levine, Vlahakes et al 1995"/>.
SAM may considered anteriorly directed mitral prolapse
<ref name="Sherrid, Gunsburg et al 2000"/>
<ref name="Sherrid, Chu et al 1993"/>
<ref name="Levine, Vlahakes et al 1995"/>.
In both conditions the mitral valve is enlarged and is displaced in systole by the pushing force of flow resulting in mitral regurgitation.
 
Because the mitral valve leaflet doesn't get pulled into the LVOT until after the aortic valve opens, the initial upstroke of the arterial pulse will be normal. When the mitral valve leaflet gets pushed into the LVOT, the arterial pulse will momentarily collapse and be followed by a second rise, as the left ventricular pressure overcomes the increased obstruction that SAM of the mitral valve causes. This can be seen on the physical examination as a double tap upon palpation of the apical impulse and as a double pulsation upon palpation of the carotid pulse, known as ''[[pulsus bisferiens]]''.


==References==
==References==

Revision as of 03:27, 15 August 2011

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Editors-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Depending on the degree of obstruction of the outflow of blood from the left ventricle of the heart, HCM can be defined as obstructive or non-obstructive. About 25% of individuals with HCM demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In other individuals obstruction only occurs under certain conditions. This is known as dynamic outflow obstruction, because the degree of obstruction is variable and is dependent on the amount of blood in the ventricle immediately before ventricle systole (contraction).

Location Of The Left Ventricular Outflow Obstruction

The left ventricular obstruction can be either

  • Mid-cavitary: the middle of the ventricle or
  • Sub-aortic: just below the aortic valve

Systolic Anterior Motion of the Mitral Valve (SAM)

If dynamic outflow obstruction is present in a patient with HCM, it is usually due to systolic anterior motion (SAM) of the anterior leaflet of the mitral valve. Systolic anterior motion of the mitral valve (SAM) may be due a subaortic bulge of the septum along with narrowing the left ventricular outflow tract, which taken together cause high velocity flow. This in turn is associated with the Venturi effect which is a local low pressure zone in the left ventricular outflow tract. This low pressure zone was thought to suck the mitral valve anteriorly into the septum. More recently, however, SAM onset has been observed to be instead a low velocity phenomenon. [1] [2]. The role of Venturi forces in the left ventricular outflow tract may be less important than previously thought. While the Venturi effect was thought to cause the abnormality in prior studies, more recent echocardiographic studies indicates that drag, which is more of a pushing force rather than a sucking force like the Venturi effect, may be the dominant hydrodynamic force acting on the mitral leaflets [1][2][3][4][5] [6].

The videos below show examples of systolic anterior motion of the mitral valve:

<youtube v=Y7JUVTXHBs0/>

<youtube v=6TWb-wIL0H0/>

Impact of Systolic Anterior Motion of the Mitral Valve: The Spike and Dome Pattern to the Carotid Pulse

Because the mitral valve leaflet doesn't get pulled into the left ventricular outflow tract (LVOT) until after the aortic valve opens, the initial upstroke of the arterial pulse pressure will be normal. When the mitral valve leaflet gets pushed into the LVOT, the arterial pulse will momentarily collapse and will later be followed by a second rise in the pulse pressure, as the left ventricular pressure overcomes the increased obstruction caused by the SAM of the mitral valve. This can be seen on the physical examination as a double tap upon palpation of the apical impulse and as a double pulsation upon palpation of the carotid pulse, known as pulsus bisferiens or a "spike and dome pattern" to the carotid pulse.

References

  1. ↑ 1.0 1.1 Jiang L, Levine RA, King ME, Weyman AE. An integrated mechanism for systolic anterior motion of the mitral valve in hypertrophic cardiomyopathy based on echocardiographic observations. Am Heart J 1987; 113:633–44
  2. ↑ 2.0 2.1 Sherrid MV, Gunsburg DZ, Moldenhauer S, Pearle G. Systolic anterior motion begins at low left ventricular outflow tract velocity in obstructive hypertrophic cardiomyopathy. J Am Coll Cardiol 2000; 36:1344–54
  3. ↑ Sherrid MV, Chu Ck, DeLia E, Mogtader A, Dwyer Jr. EM, An echocardiographic study of the fluid mechanics of obstruction in hypertrophic cardiomyopathy. J Am Coll Cardiol 1993; 22:816–25
  4. ↑ Levine RA, Vlahakes GJ, Lefebvre X, et al. Papillary muscle displacement causes systolic anterior motion of the mitral valve. Circulation 1995; 91:1189–95
  5. ↑ Messmer BJ. Extended myectomy for hypertrophic obstructive cardiomyopathy. Ann Thorac Surg 1994; 58:575–7
  6. ↑ Schoendube FA, Klues HG, Reith S, Flachskampf FA, Hanrath P, Messmer BJ. Long-term clinical and echocardiographic follow-up after surgical correction of hypertrophic obstructive cardiomyopathy with extended myectomy and reconstruction of the subvalvular mitral apparatus. Circulation 1995; 92:II-122–7
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