Evaluation of left atrium in two-dimensional and M-mode echocardiography in Brazilian boxer dogs

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Ev a lu a t ion of le ft a t r iu m in t w o- dim e n sion a l a n d M - m ode

e ch oca r diogr a ph y in Br a z ilia n box e r dogs

de Oliv e ir a Ca v a lca n t i, Gu ilh e r m e Albu qu e r qu e 1; Lá z a r o M u z z i, Ru t h n é a Apa r e cida 2; Ba r a ca t de Ar a ú j o, Robe r t o 1*

1- Fr om t he Vet er inar y School, Feder al Univer sit y of Minas Ger ais, Belo Hor izont e, Br azil, Post al code 567, Zip- code 30123- 970 ( Cavalcant i & Ar aúj o) ; 2- Fr om t he Depar t m ent of Vet er inar y Medicine, Feder al Univer sit y of Lavr as, Lavr as, Minas Ger ais, Br azil, Post al code 3037, Zip- code 37200- 000 ( Muzzi) .

* Cor r esponding aut hor . Tel/ fax.: + 55- 31- 34092280. E- m ail addr ess: bar acat @vet .ufm g.br ( R.B. de Ar aúj o) .

Abst r a ct

The Boxer dogs have high pr edisposit ion t o show dilat ed car diom yopat hy ( DC) . Consequent ly t he evaluat ion of t he left at r ium size is im por t ant t o t he assessm ent of t he sever it y of t his disease. I n t he pr esent st udy, t he aor t ic r oot ( AO) and left at r ium ( LA) dim ensions w er e ev aluat ed using t w o- dim ensional ( 2D) and M m ode ( M) echocar diogr aphy in 36 healt hy Boxer dogs. Ther e w er e used 18 m ales and 18 fem ales, r anging fr om 1.5 t o 6 year s old. A st at ist ically significant differ ence bet w een t he sexes w as obser ved for AO- M, AO- 2D, LA- M and LA- 2D. A linear r egr ession w it h body sur face ar ea w as obt ained for AO- M, AO- 2D, LA- M and LA- 2D. The LA/ AO- 2D r at io w as 1.17 ± 0.11 ( n= 36) and t he LA/ AO- M r at io w as 1.10 ± 0.11( n= 36) . The r at ios evaluat ed in t w o-dim ensional and M m ode also didn’t differ bet w een sexes in healt hy Boxer dogs.

Ke y - w or ds: Dogs, Boxer , echocar diogr aphy, Left at r ium .

I n t r od u ct ion

The left at r ium ( LA) can becom e enlar ged in size and m ass at t r ibut able t o bot h pr essur e and volum e over load in var ious car diac disease ( Hansson et al., 2002) . So, t o ident ify and classify t he degr ee hear t disease is im por t ant t o evaluat e LA size ( Haendcchen et al., 1982, Hansson et al., 2002, Muzzi et al., 2006) .

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1983, Gonçalves et al., 2002) or var ious cir cum fer ence, ar ea or volum e calculat ions ( Rishniw and Er b, 2000) . The dim ensions of LA and t he aor t a r oot ( AO) have been used t o calculat e an LA/ AO r at io, pr oducing an index for LA size. The applicat ion of t his r at io is bet t er t han using LA dim ensions nor m alized t o body w eight or body sur face area, because t he AO is an int er nal r efer ence and w as not likely t o becom e enlar ged as a r esult of com m on for m s of car diac disease ( Br ow n et al., 1974, Boon et al., 1983) .

The det er m inat ion of r efer ence values for each br eed is cr ucial in im pr oving t he accur acy of echocar diogr aphic diagnosis and br eed specific dat a ar e needed t o obt ain t he m or e nar r ow r efer ence r anges ( Cr ippa et al., 1992, Dukes- McEw an et al., 2002) . The Boxer s dogs w er e pr edisposed t o pr esent dilat ed car diom yopat hy ( Tidholm et al., 1997) , aor t ic st enosis and pulm onar y st enosis ( Boon, 1998) . I n t he pr esent st udy, t he LA/ AO index w as evaluat ed using t he t w o dim ensional and M m odes in m ales and fem ales healt hy Boxer dogs.

M a t e r ia ls a n d M e t h ods

A t ot al of 36 Boxer dogs ( 18 m ales and 18 fem ales) w er e used in t he st udy. The dogs w er e clinically healt hy, w it h ages r anging fr om one and a half t o six years old, and m ean w eight s of 27.18 kg ± 4.28. Body w eight ( Wt ; gram s) w as r ecor ded, and t he body sur face area ( BSA; m et r es2) calculat ed fr om t he follow ing for m ula: BSA= 10.1xWt0.667x10- 4. The exper im ent al pr ot ocol had t he appr oval of t he I nst it ut ional Et hical Com m it t ee at t he Feder al Univer sit y of Minas Ger ais.

Each dog w as subm it t ed t o phy sical and elect r ocar diogr aphic ( ECG) exam inat ions, non- invasive blood pr essur e ( BP) evaluat ion and r out ine echocar diogr aphic exam s using a 5Mhz pr obe1. At t he level of left dist al t ibia, t he syst olic, t he diast olic and t he m ean BP w er e m easur ed using an oscillom et r ic blood pr essur e m onit or2. ECG exam inat ions w er e per for m ed accor ding t o st andar d t echniques ( Kit t leson, 1998, Tilley, 2000) .

The LA and AO w ere m easured in M- m ode ( LA- M, AO- M) using a short axis view at t he aort ic valve level. The AO diam et er w as m easur ed on t he t im e of elect r ocar diogr aphy Q w ave and t he LA size w as m easur ed on t he t im e of elect r ocar diogr aphy T w ave ( Lom bar d, 1984) . Aft er w ar ds t he LA/ AO- M r at io w as calculat ed ( Figur e 1A) .

I n t w o- dim ensional ( 2D) , t he diam et ers of LA and AO w ere m easured sim ilar ly t o pr evious st udy ( Rishniw and Er b, 2000) . I t w as m easur ed t he int er nal shor t - axis diam et er of aor t a ( AO- 2D) along t he com m issur e bet w een

1_{Toshiba SSH-140, Toshiba Corporation, Tokyo, Japan.}

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t he noncor onar y and r ight cor onar y aor t ic valve cusps on t he t im e of elect r ocar diogr aphy Q w ave. The m easur ing of int er nal shor t - axis diam et er of t he left at r ium ( LA- 2D) in a line ext ending fr om t he com m issur e bet w een t he noncor onar y and left cor onar y aor t ic valve cusps t o t he dist ant m ar gin of t he left at r ium on t he t im e of elect r ocar diogr aphy T w ave. I n im ages w her e a pulm onary vein w as seen ent er ing t he left at r ium at t his caudolat er al locat ion, t he edge of t he LA w as approxim at ed by ext ending t he visible edges of t he left

at r ium in a cur ved fashion ( Figur e 1B) . Aft er w ar ds t he LA/ AO- 2D r at io w as calculat ed.

Figu r e 1 : The m easur em ent of aor t ic r oot ( bet w een yellow ar r ow s) and left at r ium ( bet w een gr een ar r ow s) m ade

fr om M- m ode echocar diogr aphy ( A) and

t w o- dim ensional

echocar diogr aphy ( B) in t he r ight par ast er nal shor t axis view is show ed. Not e t he m easur ed st r uct ur es values inside t he cor r espondent color ellipses. See t ext for det ails.

The ECG exam inat ions w er e m onit or ed and all r esult s w er e r ecor ded on VHS t apes for r et r ospect ive analyses.

Linear r egr ession analyses ( F- t est ) w er e calculat ed w it h t he sexes, bot h com bined and separ at ed bet w een all echocar diogr aphic

par am et er s and BSA. When t he r egr ession w as found t o be st at ist ically significant at t he 5% level, t he equat ion of linear r egr ession of BSA on t he echocar diogr aphic par am et er w as calculat ed. The St udent 's t - t est w as used t o com par e t he m ean

4 Re su lt s

Means values as w ell as all echocar diogr aphic par am et er s and BSA, separ at ely for m ales and fem ales, ar e com piled in Table 1.

Ta ble 1 . Boxer Dogs Echocar diogr aphic Measur em ent s and Body Sur face ar ea w it h Regar d t o Gender .

LA- 2D

( m m ) AO- 2D ( m m ) LA/ AO- 2D LA- M ( m m ) AO- M ( m m )

LA/ AO- M

BSA ( m2₎

m eana _{SD m ean}a _{SD m ean}a _{SD m ean}a _{SD m ean}a _{SD m ean}a _{SD m ean}a _SD

Male 23.3A _{2.3 19.8} A _{1.62 1.18} A _{0.10 26.3} A _{2.06 23.8} A _{2.51 1.11} A _{0.12 0.97} A _0.08

Fem ale 20.6 B _{2.5 17.6} B _{1.37 1.17} A _{0.13 23.4} B _{1.54 21.6} B _{1.56 1.09} A _{0.11 0.85} B _0.07

a _{Different capital letters to same column represent difference (P<0.05). LA-2D, left atrium measured on a two-dimensional image;}

AO-2D, aorta measured on a two-dimensional image; LA/AO-AO-2D, ratio between left atrium and aorta measured on a two-dimensional image expressed as an index; LA-M, left atrium measured in M-mode; AO-M, aorta measured in M-mode; LA/AO-M, ratio between left atrium and aorta measured in M-mode expressed as an index; BSA, body surface area in m2; S.D., standard deviation.

The linear r egr essions bet w een echocar diogr aphic indices and BSA ar e illust r at ed in Table 2.

Ta ble 2 . Effect of body sur face ar ea on echocar diogr aphic par am et er s.

p a ra me te rs Re g re ssio n e q ua tio n R2 _{Ad juste d R}2

LA-M 13.225+12.812xBSA 0.28** 0.26**

AO -M 11.560+12.209xBSA 0.25** 0.23**

LA-2D 9,722+13,456xBSA 0.23** 0.20**

AO -2D 11,125+8,359xBSA 0.19** 0.16**

Males and females combined. **P<0.01. BSA, Body surface area in m2_{. LA-M, left atrium measured in M-mode; AO-M,}

aorta measured in M-mode; LA-2D, left atrium measured on a two-dimensional image; AO-2D, aorta measured on a two-dimensional image.

The BSA of m ale dogs ( 0.97±0.08) w as higher t han for fem ale dogs ( 0.85±0.07) , t his differ ence w as st at ist ically significant ( P< 0.05) .

The LA/ AO- 2D and LA/ AO- M indexes w er e sim ilar in m ales and fem ales. The linear r egr ession analysis also no indicat ed a significant cor r elat ion bet w een LA/ AO- 2D or LA/ AO- M indexes and BSA.

D iscu ssion

Evaluat ion of left - hear t disease alw ays includes assessm ent of t he size of t he left at r ium ( Boon et al., 1983) , and t his evaluat ion can be det er m ined using 2D or M- m ode by echocar diography ( Rishniw and Er b, 2000, Hansson et

al., 2002) .

The m ost im por t ant differ ence bet w een t he 2D and t he M- m ode m et hod is t hat t he M- m ode cur sor oft en t r ansect s t he left aur icle ( r at her t han t he body of t he left at r ium ) in dogs because of differ ent posit ioning of t he hear t com par ed t o hum ans. Thus, pr evious invest igat ors m ight som et im es have inadver t ent ly com par ed t he size of t he left aur icle and not t he left at r ium t o t he aor t a ( Figur e 2) ; I n nor m al dogs, t he LA/ AO- M w ould be expect ed t o be sm aller t han LA/ AO- 2D ( Hansson et al., 2002) .

Figu r e 2 : The m easur em ent of aor t ic r oot and left at r ium m ade fr om M- m ode echocar diogr aphy. The st andar d M- m ode cur sor posit ion ( yellow line) for m easur ing aor t ic r oot diam et er usually t r ansect s t he left at r ium ( LA) near it s aur icle, t her efor e under est im at ing t r ue LA size.

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( 1.7±0.2) ( O’Lear y et al., 2003) , Est rela Mount ain dogs ( 1.23±0.21) ( Lobo et

al., 2008) and Whippet s ( 1.4±0.1) ( Bavegem s et al., 2007) , but lar ger t han

nor m al Cavalier King Char les spaniel ( 1.03±0.09) ( Hansson et al., 2002) . I t suppor t s t hat t he det er m inat ion of r efer ence values for each br eed is im por t ant , and t he m axim um nor m al value of LA/ AO- 2D of 1.6 ( Rishniw and Er b, 2000) should be r evised for each br eed, and gauge of LA and AO m easur em ent in 2D m ode m ust be done.

Most of t he echocar diogr aphic st udy ( Rishniw and Er b, 2000, Hansson et al., 2002) m easur ed t he LA- 2D and AO- 2D on t he 1st fr am e r at e aft er aor t ic valve closur e. I n t he pr esent st udy, w e do t he m easur em ent s of LA- 2D ( at syst ole) and AO- 2D ( at diast ole) w it h elect r ocar diogr aphic param et er s. The m easur em ent s in t his st udy w er e sim ilar t o anot her w or k ( Rishniw and Er b, 2000) , w hich evaluat ed differ ent br eeds of dogs and obt ained m ean LA/ AO- 2D t o 1.31.

I n anot her st udy ( Hansson et al., 2002) , it w as com par ed t he LA/ AO- 2D r at io and LA/ AO- M in 56 nor m al dogs and 110 dogs w it h m it r al r egur git at ion. No differ ence w as seen bet w een M- m ode and 2D derived LA/ AO indices in nor m al dogs ( 1.01±0.13 and 1.03±0.09) . How ever , in dogs w it h m it ral r egur git at ion, t he LA/ AO- 2D ( 1.61±0.57) w as significant ly gr eat er t han t he LA/ AO- M ( 1.42±0.51) , so t he 2D index is m or e sensit ive t o LA enlar gem ent t han t he M- m ode index.

I n t he pr esent st udy, t he dogs had LA/ AO- M of 1.10±0.11, w it hin t he expect r ange of 0.8- 1.3 ( Bonagur a, 1983, Lom bar d, 1984) , but ar e slight ly lar ger t han cavalier King Char les spaniels ( 1.01±0.13) ( Hansson et al., 2002) , Ger m an Shepher d dogs ( 0.9±0.08) ( Kayar et al., 2006) ; ( 0.97±0.09) ( Muzzi et

al., 2006) , and in st udies w it h differ ent br eeds ( Lom bar d, 1984) .

I n our st udy t he echocar diogr aphic m easur em ent s w er e lit t le significant ly cor r elat ed w it h BSA ( Table 2) , in agreem ent w it h a pr evious w or k ( Cr ippa et

al., 1992) , but fr equent ly t his cor r elat ion var ies ( Gonçalves et al., 2002, Kayar et al., 2006) . These r esult s suggest t he exist ence of car diac m or phological and

funct ional hom ogeneit y for t his br eed and age w it hout any pr ecise r elat ion w it h body w eight .

I n agr eem ent w it h t his st udy, previous invest igat or s ( Lom bar d, 1984, Rishniw and Er b, 2000) dem onst r at ed t hat no cor r elat ion occur r ed bet w een LA/ AO r at io and bodyw eight , suggest ing t hat t his m easurem ent is independent of body w eight .

Ack n ow le dgm e n t

We t hank t he Nat ional Council for Scient ific and Technological Developm ent ( CNPq) , for t he scholar ship aw ar ded t o G. A. de O. Cavalcant i

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Recibido 07.09.09 - Ref.prov. SEP0908B - Revisado: 10.12.09 - Aceptado 18.12.09

Ref. def. 011024_REDVET - Publicado: 01.01.10

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