Pilgram, Anna (2018):
Left ventricular volume quantification using the monoplane and biplane Simpson’s method of discs in healthy dogs and in dogs with degenerative mitral valve disease.
In human medicine the biplane Simpson’s method of discs (SMOD) is an established method in case of the quantification of left ventricular functional parameters while in veterinary medicine it is rarely used. Reason for this are among other things the lack of studies, which are dealing with a greater range of pedigrees and sizes of the study population of dogs and which moreover could establish reference values for this heterogeneous group, which are able to detect a volume overload as well. Until now, most studies dealt with breed specific reference values, which were normalized to the body surface area (BSA). Moreover, it is not completely clarified if the monoplane SMOD including only one of the chamber views might be sufficient in dogs. During the progression of the degenerative mitral valve disease (DMVD), which turned out to be the most common heart disease in dogs, the left ventricular enddiastolic volume (EDV) and in later stages the endsystolic volume (ESV) might be increased.
Consequently the volume quantification using the SMOD is meaningful, also concerning treatment decisions.
In the present studies on the one hand it should be clarified if the preferred utilization of the biplane method in human medicine could be transferred in the veterinary field.
This was examined in the first study on the basis of a heart-healthy study population.
Moreover, a suitable indexation method of the left ventricular volumes (LVV) was investigated, which shows the least remaining influence on body weight after applying the indexation on the data. In the second study monoplane and biplane SMOD in dogs of varying stages of DMVD were compared.
The study population consisted of 126 private owned patients of the University of Veterinary Medicine Hannover, which were presented for a routine echocardiographic examination. All dogs underwent echocardiographic examination and were, after staging them into groups, analyzed by the external analyses software
Summary
EchoPac® (EchoPac PC, 108.1.4 Version 110.x.x, analyses software; GE Healthcare, Horten/Norway). The acquisition of SMOD-volumes was made biplane by the left-apical four- and two-chamber view, and additionally monoplane by only one singular plane using the left-apical views or the right-parasternal four-chamber view.
In the first study LVV of 38 dogs were collected (age: 1-14 years; body weight: 3.5-27 kilogram). Initially raw data of EDV and ESV were indexed to body weight (BW), BSA and aortic root diameter (AoD). The calculation of the coefficient of determination (r2) as well as the application of linear regression showed, that data which were normalized on BW (EDV/kg; ESV/kg) showed the least remaining dependence to the body weight (r2; BW: < 0.08; BSA: > 0.39; AoD: > 0.62). Moreover by the means of linear regression and an allometric formula there was calculated a suitable scaling exponent for BW, which shows the least remaining dependence of the indexed data to the body weight of the dogs. The scaling exponents b for EDVI2 and ESVI2
(EDV/kgᵇ; ESV/kgᵇ), which were calculated individualized for each monoplane and biplane SMOD volumes, were all approximately 1 (0.96 – 1.01). Consequently in such a heterogeneous study population normalization by BW (EDVI1, ESVI1) is recommended, because of the fact that the calculated scaling exponents of EDVI2
und ESVI2 confirmed this as well.
The comparison of monoplane, using the left-apical four-chamber view, and biplane SMOD revealed significant differences using least significant difference (LSD) tests (EDVI2, p = 0.01; ESVI2, p = 0.03). The comparison of the left-apical biplane and monoplane SMOD, using the right-parasternal four-chamber view, as well as the comparison of both left-apical monoplane SMOD revealed no significant differences.
Between the left-apical and the right-parasternal four-chamber views, there were only significant differences for ESVI2 (p = 0.02), but not for EDVI2. Moreover there were detected significant differences between the methods concerning enddiastolic and endsystolic measurements of the LV maximum length, which suggests frequently foreshortened depictions of the LV.
In the second study 88 (age: 3.7-18.1 years; body weight: 2.6-29.1 kilogram) dogs with varying stages of DMVD were examined (B1: n = 50; B2: n = 22; C: n = 16). For
Summary
the classification of the different stages of the DMVD (CHIEF B-C) using the system of Canine Heart failure International Expert Forum (CHIEF), former published measurement quantities like the Cornell-index and the left atrial-to-aortic root ratio (LA/Ao) were relevant.
CHIEF B1 no clinical symptoms, no signs of cardiac compensation (LA/Ao < 1.6 and Cornell-index EDD < 1.85 (95% confidence interval))
CHIEF B2 no clinical symptoms, but with signs of cardiac compensation (LA/Ao ≥ 1.6 and/or Cornell-index EDD ≥ 1.85)
CHIEF C clinical symptoms and a radiographically proven lung edema
McNemar`s test revealed no significant diagnostic differences of the monoplane and biplane EDVI in detecting a volume overload. For group-comparison single factor variance analyses as well as a paired T-test for multiple pairwise comparisons were performed, which showed for EDVI1, in contrast to the healthy population, no significant differences between the monoplane and biplane SMOD. The differences of the ESVI1 between the methods were very variable. There could be detected a significant increase of EDVI1 with every progression of DMVD stage. On the contrary the increase of ESVI1 could be detected only in stage B2 and C. This was uniform for monoplane and biplane SMOD.
In the context of this work, the first study could generate volume indices for the monoplane and the biplane SMOD on the basis of a healthy, mixed-breed dog population. In order to normalize the volumes, BW in kilogram seems to be most suitable. Therefore, in case of a DMVD and additionally an unclear presence of ED volume overload, following upper cut-off values for the indices can be used (95%
percentile): for the biplane SMOD > 2.98, for the monoplane method using the left-apical four-chamber view > 2.90, left-left-apical two-chamber view > 3.00 and using the right-parasternal four-chamber view > 2.72. Both, the healthy study group and the diseased dogs, showed limitations concerning the monoplane SMOD. However, the left-apical four-chamber view seems to identify a LV EDV-overload already in stage B1, wherefore this chamber view appears to be recommendable in the evaluation of
Summary
dogs with DMVD. Moreover, the utilization of the biplane SMOD showed no clear diagnostic benefit, even though this method presumable demonstrates fewer limitations in displaying the “real” LVV. The EDVI measured by the SMOD using the right-parasternal four-chamber view showed to be, for the healthy as well as for the diseased study group, identical with those of the left-apical four-chamber view.
Though, the comparison of ESV revealed exclusively significant smaller values for the right-parasternal four-chamber view, therefore its only measurement is not recommended.
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