Does the Aortic root contract or relax during ventricular systole ?

Does the Aortic root contract or relax during ventricular systole ?

Does the Aortic root contract or relax during ventricular systole ? Some time back I asked this question in one of my classes for the fellows and found no takers. Not even a guess? I realized later it was indeed a tough question. The heart is not the only dynamic organ as we generally believe. The entire aorta which is the extension of the left ventricle has to be dynamic according to the physics of ventricular-arterial coupling and the momentum of blood flow.

What happens to the aortic dimension with systole?

Even prior to systole, there is evidence, Aorta gets ready to receive the blood from the LV. So, the Aortic root is larger at the onset of systole. (Ref 2 It is been generally agreed now, that systolic dimensions are slightly more by a few mm. That is why aortic dimensions are measured in peak systole as per the American society of echocardiography.

There has been an opposite argument as well. The diastolic aortic dimension must be definitely a little larger when the aortic valve is in the closed position and the aortic root becomes a reservoir of blood that’s meant to be distributed during diastole. What determines the aortic dimension on a moment-to-moment basis? Is it the, LV contractility, pressure, or volume, or the compliance of the aortic wall that determines the aortic dimension and pulsatility? How does a prosthetic valve alter this?

Where can we get the answer?

A wonderfully done study from University Medical Center Utrecht, Utrecht, The Netherlands tries to tell us This ECG-gated CT scan in 108 Aorta.(Ref 1)

It is not at all surprising to note the aortic root behaves independently.It either contracts or relaxes ( as it wishes) with a range of 4 mm swing on either side of the systole and diastole. Another stunning fact is, it remains static in a significant number. (One possible explanation is the true aortic annulus is less dynamic because is bordered by a fibrous skeleton while the rest of the aortic root only contracts during systole)

Clinical implication of aortic pulsatility

The implication of knowing (or not knowing )the dynamism of the aorta can be huge.

  • Age-related stiffening and onset of systolic hypertension
  • Aortic diameter, dynamism, and shear stress is a key parameters in initiating the dissection and its propagation
  • Choosing the right sized valve for AVR
  • Understanding the dynamism of the aortic root is absolutely important as the current interventional heart-throb TAVI involves just a passive placement in the aortic root. Imagine what will happen to foundations that are excessively dynamic and shaky.

Final message

Though the aorta is an extension of LVOT, it doesn’t seem to be in complete sync with the cardiac cycle. It tends to have an independent behavior, out of phase with the heart. Aortic root size can either increase, decrease, or be static in response to LV contractility. It is a surprising finding in this era of TAVI, we lack clarity on what exactly happens to aortic roots during various phases of the cardiac cycle. (No doubt, paravalvular leak migration of TAVI remains a major worry, that has a direct relationship with pulsatility of the aortic root ) One thing is obvious,.Young cardiologists have a lot of work to do.

Reference Heer LM, Budde RP, Mali WP, de Vos AM, van Herwerden LA, Kluin J. Aortic root dimension changes during systole and diastole: evaluation with ECG-gated multidetector row computed tomography. Int J Cardiovasc Imaging. 2011 Dec;27(8):1195-204.

2. Pang DC, Choo SJ, Luo HH, et al. Significant increase of aortic root volume and commissural occurs prior to aortic valve opening. J Heart Valve Dis. 2000;9:9–15. [PubMed] [Google Scholar]

3. Vesely I. Aortic root dilation prior to valve opening is explained by passive hemodynamics. J Heart Valve Dis. 2000;9:16–20. [PubMed] [Google Scholar]




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