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 an 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, the aorta gets ready to receive the blood from the LV. So, the Aortic root must be larger at the onset of systole. (Ref 2 ) It is been generally agreed now, that the systolic dimension is 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 could be larger, as the aortic valve is in the closed position and the aortic root distended, & 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?
So, what exactly happens to the aortic dimension during the cardiac cycle ?
A wonderfully done study from University Medical Center Utrecht, The Netherlands throws some important facts with their analysis of ECG-gated CT scans in 108 Aortas.(Ref 1)
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, pulsatility, and shear stress are the key parameters in initiating dissection and its propagation
- Choosing the right sized valve for AVR
- Current interventional heart-throb TAVI involves just a passive placement of the valve in the aortic root. Imagine what will happen, if the foundations are excessively dynamic and shaky
It is surprising, even after decades of vascular research, we lack clarity on what exactly happens to aortic root during various phases of the cardiac cycle. (Currently, paravalvular leak, & migration of TAVI remains a major worry, which has a direct relationship with pulsatility of the aortic root ) One thing is obvious,.Young cardiologists have a lot of work to do in this arena.
Final message
Though the aorta is a direct extension of LVOT, its vaso-motion 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.
As per available evidence, the aortic root dimension can either increase, decrease, or be static in response to LV contractility.
Reference
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]
Dr.S.Venkatesan MD 