My patient with aortic sclerosis has a loud systolic ejection murmur. What is the exact mechanism of this murmur?

We usually blame cardiac murmurs on the “turbulence” caused by blood flowing past an irregular valve surface but, believe it or not, how the murmur is created has been a matter of controversy. 1-4

For sure, murmurs are generated by disturbance of laminar blood flow (ie, turbulence) but over the years many have argued that turbulence per se fails to produce adequate acoustic force to be audible at the chest wall.2 Although challenged by some,1  the concept of “vortex shedding” borrowed from fluid dynamics is fascinating and has been proposed as a potential explanation.

Per this theory, just as a boulder causes a stream to separate and generate vortices, valves (particularly when abnormal) also create vortices. As the vortices are shed near the valve, they leave in their place relatively calm wakes which are then rapidly filled by flowing blood, creating the sound of a murmur.  

Two important variables in this theory are velocity and viscosity. When the velocity of blood flow increases substantially as in high cardiac output states (eg, fever, pregnancy), vortex shedding and the intensity of the murmur also increase. Similar phenomenon may be expected when the blood viscosity is lowered (eg, in anemia).

 

References

  1. Sabbah HN, Stein PD. Turbulent blood flow in humans: Its primary role in the production of ejection murmurs. Circ Res 1976;38: 513-24. https://www.ncbi.nlm.nih.gov/pubmed/1269101
  2. Alpert MA, Systolic murmurs. In Walker HK, Hall WD, Hurst JW. Clinical methods: The history, physical, and laboratory examinations. 3rd ed. Butterworths, Boston, 1990. https://www.ncbi.nlm.nih.gov/books/NBK345/
  3. Bruns D. A general theory of the causes of murmurs in the cardiovascular system. Am J Med 1959;27:360-74. http://www.amjmed.com/article/0002-9343(59)90002-6/fulltext
  4. Guntheroth WG. Innocent murmurs: A suspect diagnosis in non-pregnant adults. Am J Cardiol 2009;104:735-7. https://www.ncbi.nlm.nih.gov/pubmed/19699354
My patient with aortic sclerosis has a loud systolic ejection murmur. What is the exact mechanism of this murmur?

What’s ACNES (anterior cutaneous nerve entrapment syndrome)?

 As the name implies, this is an abdominal pain syndrome thought to be due to the entrapment of cutaneous branches of an intercostal nerve at the level of the rectus abdominis muscle (1,2).   It may be acute or chronic.

Up to a third of patients with chronic abdominal pain may have ACNES with the source of pain attributed to the abdominal wall, not the viscera (1,3).  Unfortunately, a third of patients with ACNES experience pain for >1 year and about 10% for > 5 years before diagnosis of ACNES is made.

In about one-half of cases, ACNES begins spontaneously, with the remainder developing after abdominal surgery or pregnancy, or is associated with “sports”, “job” or “unusual activity” (4).   Females outnumber males by a 4:1 margin with an average age of 37  y (2).  Carnett’s sign on physical exam may be a clue (2,5) with a sensitivity of 78% and specificity of 88% for abdominal wall pain (6) .

Identification of abdominal wall trigger points and their infiltration with lidocaine may relieve the pain instantaneously and can serve as a diagnostic test.  Surgical neurectomy may be effective in those with only temporary or partial response to repeated lidocaine injections (1).

 

References

1. Boelens OBA, Scheltinga MR, Houterman S, et al. Randomized clinical trial of trigger point infiltration with lidocaine to diagnose anterior cutaneous nerve entrapment syndrome. Br J Surg 2013;100:217-221. https://www.ncbi.nlm.nih.gov/pubmed/23180371

2. van Assen T, Brouns JAGM, Scheltinga MR, et al. Incidence of abdominal pain due to anterior cutaneous nerve entrapment syndrome in an emergency department. Scand J Trauma Resusc Emerg Med 2015;23:19. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4327965  

3. van Assen T, de Jager-Kievit JW, Scheltinga MR, et al. Chronic abdominal wall pain misdiagnosed as functional abdominal pain. J Am Board Fam Med 2013;26:738-44. https://www.ncbi.nlm.nih.gov/pubmed/24204070

4. Boelens OB, Scheltinga MR, Houterman S, et al. Management of anterior cutaneous nerve entrapment syndrome in a cohort of 139 patients. Management of anterior cutaneous nerve entrapment syndrome in a cohort of 129 patients. Ann Surg 2011;254:1054-1058.  https://www.ncbi.nlm.nih.gov/pubmed/21881494

5. Pearls4Peers.  https://pearls4peers.com/2016/12/20/in-my-patient-with-abdominal-pain-what-physical-exam-finding-can-help-differentiate-abdominal-wall-from-intra-abdominal-sources-of-pain

6. Sweetser S. Abdominal wall pain: a common clinical problem. Mayo Clin Proc 2019;94:347-355. https://www.mayoclinicproceedings.org/article/S0025-6196(18)30671-2/fulltext

 

 

What’s ACNES (anterior cutaneous nerve entrapment syndrome)?