April 2024

In this VETgirl online veterinary continuing education blog, Dr. Christopher Kennedy, DACVECC, DECVECC discusses subjective assessment of left ventricular systolic function on Focused Cardiac Ultrasound (FCU) in the dog and cat.

By Dr. Christopher Kennedy, DACVECC, DECVECC

Subjective assessment of left ventricular systolic function on Focused Cardiac Ultrasound

The goals of this blog are:

1. Image the left ventricle from multiple angles
2. Subjectively identify normal and reduced systolic function

The views:

  • PLAX4
  • PSAX-pap
  • SX-heart

Objective and subject assessments
Objective assessment requires measurement. This may be, for example, a length, area, volume, ratio, or percentage. Benefits include meaningfulness, quantification and comparability: fractional shortening (FS) of 10% means something and is quantitively different to FS of 40%, and FS of 10% yesterday versus 30% today implies improvement. However, objective assessments require measurement of appropriately acquired images, thus incur measurement and acquisition error, which can be misleading. For example, if the left atrial-to-aortic ratio is 1.9 (normal < 1.6), this means something and quantifies worse severity than a value of 1.5; however, if the measurement is incorrect, then the value is meaningless and what is quantified is only error. This can be disastrous if, for example, fluids are withheld from a patient in hypovolemic shock due to mis-quantification. This highlights the necessity for clinical integration and reminds us that FCU is only one tool in our toolbox.

Subjective assessment of the left ventricle (LV), also called “eyeballing”, is common practice in human emergency medicine.(1)  It requires no measurements, though still requires good image quality. Subjective assessment performed by human emergency clinicians had approximately 90% sensitivity and 85% specificity for identifying normal and reduced systolic function.(1)  We must remind ourselves of the species differences and the training difference between veterinarians and human clinicians. Recent data indicates that human clinicians are better at subjectively identifying normal and extremely decreased systolic function, rather than lesser grades of systolic dysfunction.(2)  We feel this is likely true for veterinarians too, though it is yet to be investigated.

This is the simplest form of subjective assessment of the LV. It is mandatory to image the LV from at least two views. Start with the PLAX4, then move to the PSAX-pap (See videos 1 & 2). Recording clips (cine loops) is helpful so you can review your images.

Video 1: PLAX4 view with normal systolic function. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Video 2: PSAX-pap with normal systolic function. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

From here, we can subjectively assess the systolic function with subjective statements like “systolic function seems OK” or “… seems decrease” or “… seems markedly decreased” (See videos 3 & 4). Logically, if systolic function seems OK, it is unlikely to be the cause of the presenting pathology – a dog with severe pulmonary edema is unlikely to have cardiogenic edema due to LV systolic dysfunction if it is contracting OK. Oppositely, if a dog is hypotensive with minimal systolic contraction, it is likely that the LV is contributing, at least in part, to the clinical presentation.

Video 3: PLAX4 view with markedly decreased systolic function. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Video 4: PSAX-pap view with markedly decreased systolic function. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

It is not appropriate to start with the PLAX-pap, as this provides only a limited short-axis slice of the LV, causing us to hyper-focus on and over-interpret the limited information within this view. Start with the PLAX4, transition to the PSAX-pap and consider adding SX-heart, particularly when other views are difficult to obtain accurately.

In PSAX-pap, focus on correct image acquisition: try to keep the LV circular, with the RV visible as a crescent in the near field, and both papillary muscles clearly demarcated in the far field. To ensure good positioning, tilt up to the mitral valve and then tilt back down just below the leaflets to image the widest section of the LV (See video 5). If your sector is too far apically, you will reduce to size of the lumen and can over-estimate the systolic function.

Video 5: Up to the mitral valve then down. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Sometimes we see a hypercontractile LV (See video 6). This can be found in various states, such as sympathetic stimulation (e.g., hypovolemia, tachycardia) and reduced afterload (e.g., sepsis and large mitral regurgitations). Quantitively, this would be FS > 55% or ejection fraction > 60%. Subjectively, we can call this “hypercontractile”, “increased” or “normal-to-increased systolic function.” Importantly, we are referring to systolic function (i.e., given the current loading conditions), so it would be wrong to say that the contractility is increased – it may be, but we cannot assess this via FCU.

Video 6: PSAX-pap hypercontractile. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Eyeballing-2.0: lines and dots
Eyeballing-1.0 is quick and easy… and often superficial. Adding mental lines or dots to your image slows down your thinking, forcing you to interrogate the LV in more detail (See videos 7 – 10).

Video 7: PLAX4 with lines. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Video 8: PSAX-pap with lines. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Video 9: PLAX4 with a dot. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Video 10: PSAX-pap with a dot. Video courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Using this technique, we ask ourselves three questions:

1. Are LV walls in all four quadrants moving centripetally?
2. Are the LV walls thickening in all four quadrants?
3. Is the lumen reducing in all four quadrants during systole?

This way, we consider the entire LV that is visible on the screen. It may be helpful for scaling systolic dysfunction (i.e., mild verses marked dysfunction). Eyeballing-2.0 also helps to identify regional wall motion abnormalities, though we don’t see them too often in veterinary FCU: if you are suspicious for one, ask a cardiologist for help.

We can use M-mode for eyeballing – again, it is important to use two views. When eyeballing the M-mode output, we look at both the interventricular septum and the LV free wall (See Figure 1). Ideally, an ECG will be used concurrently.

Figure 1: PSAX-pap M-mode of two dogs with normal systolic function (a) and markedly decreased systolic function (b). Photo courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Sometimes, we see differences between the septum and the free wall. Figure 2 shows a cat with a myocardial scar: the LV free wall isn’t moving much. In volume overloaded LVs, we can sometimes see “exuberant septal motion”, as the overload displaces the septum rightward in diastole: in diastole, the septum is relatively more anterior in the M-mode graph and moves relatively further posteriorly than the LV free wall moves anteriorly.(3)  These FCU findings are not sufficient alone to make sweeping statements on systolic function or volume status and they do not sufficiently describe cardiac performance. However, they may raise your suspicions and could be reasons to chat to your friendly neighborhood cardiologist.

Figure 2: PLAX4 M-mode of a cat with infarction of the left ventricular free wall. Note that the posterior wall on the M-mode graph does not move. Photo courtesy of Dr. Christopher Kennedy, DACVECC, DECVECC

Eyeballing: can we use it?
Subjective assessments improve with experience and good image acquisition. Often, we might assess systolic function as good and the cardiologist assesses it as reduced, or vice versa. Though evidence-based recommendations are lacking in veterinary medicine, our little FCU bag of tricks contains a few more tips for improving subjective assessments, which we can discuss in future posts. For now, focus on the overt and the obvious: try to subjectively assess LV systolic function as “seems OK” or “seems markedly decreased.” Asking a cardiologist for help with systolic function assessment can be extremely helpful and enlightening.

References and further reading
1. Albaroudi B, Haddad M, Albaroudi O, Abdel-Rahman ME, Jarman R, Harris T. Assessing left ventricular systolic function by emergency physician using point of care echocardiography compared to expert: systematic review and meta-analysis. Eur J Emerg Med. 2022 Feb 1;29(1):18-32. doi: 10.1097/MEJ.0000000000000866.
2. Raksamani K, Noirit A, Chaikittisilpa N. Comparison of visual estimation and quantitative measurement of left ventricular ejection fraction in untrained perioperative echocardiographers. BMC Anesthesiol. 2023 Apr 1;23(1):106. doi: 10.1186/s12871-023-02067-3.
3. Bonagura J and Luis Fuentes V. Echocardiography. In: Mattoon JS and Nyland TG (editors), Small Animal Diagnostic Ultrasound (2nd ed.). Elsevier Saunders, St Louis, Missouri, USA.

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