A common question asked of me from intermediate-level learners of echocardiography is how to obtain and measure isovolumic relaxation time (IVRT). However, it is important to understand that IVRT can be prolonged, normal, or short in patients with diastolic dysfunction, so its utility as a standalone measure, and/or without a full understanding of the factors which influence it, is very low.
| In mild diastolic dysfunction and ageing, the left ventricle experiences delayed relaxation, and IVRT is increased. In advanced diastolic dysfunction with restrictive filling, blood is forced out of the high pressure left atrium, and IVRT is shortened. |
Isovolumic relaxation time is the time between aortic valve closure, and the onset of diastolic filling. There is a time delay between these two events because, when the aortic valve closes at end-systole, the left ventricle is still at its fully contracted state – therefore, left ventricular pressures are still high. It takes time for the left ventricle to begin to relax and pressure to fall, before left ventricular pressure is sufficiently low (i.e. below that of the left atrium) for the mitral valve to snap open and blood to be sucked from the left atrium into the left ventricle.
If left ventricular relaxation is impaired, then it is going to take longer than normal for the ventricle to relax and pressures to fall sufficiently for diastolic filling to begin, hence IVRT will be prolonged. In a young patient, combined with other parameters for diastolic function assessment, this could be an early warning sign (e.g. of HCM in a cat). In an elderly patient, this is considered an inevitable part of the ageing process.
If diastolic dysfunction is progressive and not due to age, then in time, IVRT will start to shorten again, because left atrial pressure will become so elevated that it exceeds left ventricular pressure much sooner. In other words, the driving factor in filling becomes the elevated left atrial pressure, rather than the drop of left ventricular pressure.
In advanced diastolic dysfunction where IVRT becomes very short, there’s barely any discernible time delay between aortic valve closure and the onset of early diastolic filling at all – driven by the ‘push’ of the pathologically high left atrial pressure.
We can measure this time delay as the space between the end of the aortic outflow wave, and the beginning of the mitral E wave.
Along with IVRT, other tools for assessing diastolic function in cats and dogs include:
If you are not confident in assessing diastolic function in your patients, but would like to be, please book a call with me here. You might have one simple question I can answer on the call that will lead to an ‘ah ha!’ moment, or you might want to discuss your suitability for our full Confidence in Echocardiography training programme. Either way, I’d love to hear from you! You can also sign up to our monthly newsletter here.
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