Z va score in Aortic stenosis : No more a theoretical concept
It was the final case on weekend Echocardiogram review day, I asked my fellow for a brief summary of the patient.
“Yes, sir, he is a 62-year-old male retired govt officer. He has a severely stenosed aortic valve, with a peak gradient of 90 mmHg and a mean gradient that comes to almost 50 mmHg. LV EF is 58%, GLS is 18, LVH is obvious. LA is not dilated (Didn’t measure volume though), but DT is short. Valve orifice is hovering around 1cm, mild calcium noted in LCC I am not sure whether it’s bi or tricuspid still. The annulus is 22mm. The mitral valve is perfect, no calcium spill over to the mitral curtain and the rest of the annulus”.
“That is ok, what for he has come”?
“A GP from Tambaram has referred him after he detected a murmur over the chest”.
“Oh Ok. What are his symptoms”?
“He is denying any symptoms”.
“Are you sure? did you ask him specifically about it during exertion”?
“Yes, sir, he says he can climb 3 flights of stairs. (In fact, he was sort of amused when I told him to be frank in his expression, and he has a potentially serious obstruction in the main valve that connects his heart and body.”
“I agree, but his reaction was not so inappropriate I thought, after all, he didn’t feel any symptoms right”.
“So what shall we do for him? TAVR? SAVR? Leave him alone? Shall we put him on the treadmill? to document symptoms? Is it that risky”?
“But sir, he says he can jog for a mile or two every day”
“That’s fine. Can you really predict when his ventricle will fail and he may require a semi-emergency procedure?
“I think we can’t, but why is he is so asymptomatic sir”?
“Wow, that’s more than a million-dollar question. You need to address that to the vascular Goddess. I don’t know? ( It is all about the ability of the heart to perfectly balance the ventricle and aorta in spite of severe obstruction; It is something like TIMI 3 flow and good FFR in a patient with 90% occlusion.) My guess is, the LV does this by modulation of systemic pressure & resistance in such a way. it neither feels the strain nor does it reduce the stroke volume much. Meanwhile, Have you heard about this? Z- Va score. I would like you to read about that. It will help you understand the hemodynamic nuances of severe AS and how the ventricle manages to serially couple the afterload of the vascular system”.
“Make a pardon, I haven’t heard about it. What is Zva?
“Never mind. It is not a new index. Was first introduced 16-years ago by Martin Briand et al from Quebec, heart Institute Canada J Am Coll Cardiol . 2005 Jul 19;46(2):291-8. Z Va score(Valvulo-Arterial) is the collective flow impedance of the aortic valve and the entire aorta. It is more attractively defined as the cost of blood pressure in mmHg for pushing one ml of blood per body square meter area
Unit : mmhg /ml/m²
Normal value: < 3.5 to 4.5 (Actually no normality, rather it must be acceptable value .It is still being defined ) if the cost is more than 5mmhg it suggests significant Aortic stenosis) A high value > 4.5 is a definite index of poor outcome. In a well-compensated heart, Zva is maintained far less than 5 and many such patients are asymptomatic as well. Zva has specific clinical value in all critical AS especially so if they are asymptomatic. It is no longer a research topic, has an important role in the bedside too. Here is an excellent resource on Z Va score from ESC.
The timing of AVR in aortic stenosis is very critical. All symptomatic AS must be immediately intervened. Currently, with surgical risk falling rapidly ( & the option of TAVR looming large) even many of the asymptomatic AS need to be considered for valve intervention at the earliest before or at the onset of LV dysfunction. Zva’s score will definitely add more light to our limited hemodynamic wisdom in aortic stenosis(Zeineb HachichaJACC 2019)