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Pathophysiology ofCyanotic Congenital Heart
Defects
Muhammad AliPediatric Cardiology
Division
University of SumateraUtara
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Clinical Cyanosis
DETECTION OF CYANOSIS • Cyanosis is a bluish discoloration of the skin and mucous
membranes resulting from an increased concentration ofreduced hemoglobin to about 5 g/100 mL in thecutaneous veins.
• This level of reduced Hb in the cutaneous vein may resultfrom either desaturation of arterial blood or increasedetraction of oygen by !eri!heral tissue in the !resenceof normal arterial saturation "e.g.# circulatory shock#
hy!ovolemia# vasoconstriction from cold$.
• Cyanosis associated %ith desaturation of arterial blood iscalled central cyanosis& cyanosis %ith normal arterialoygen saturation is called !eri!heral cyanosis.
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• Cyanosis is more difficult to detect in children %ith dark!igmentation.
• 'lthough cyanosis may be detected on many !arts of thebody# the ti! of the tongue is a good !lace to look forcyanosis& the color of the tongue is not affected by raceor ethnic background# and the circulation is not sluggishin the tongue.
• (n a ne%born# acrocyanosis may cause confusion.
• (n addition# some ne%borns are !olycythemic# %hich
may contribute to the a!!earance of cyanosis %ithoutarterial desaturation.
• (n older infants and children# chronic subclinicalcyanosis !roduces clubbing.
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CAUSES OF CYANOSIS
Reduced Arterial Oxygen Saturation (i.e., Central Cyanoi! • INADE"UATE A#$EO#AR $ENTI#ATION
Central nervous system de!ression
(nade)uate ventilatory drive "e.g.# obesity# !ick%ickian syndrome$*bstruction of the air%ay# congenital or ac)uired
+tructural changes in the lungs and/or ventilation,!erfusion mismatch "e.g.# !neumonia# cystic
fibrosis# hyaline membrane disease# !ulmonary edema# congestive heart failure$
-eakness of the res!iratory muscles.• Deaturated %lood %y&aing e''ectie aleolar unit
(ntracardiac right,to,left shunt "i.e.# cyanotic congenital heart defect$
(ntra!ulmonary shunt "e.g.# !ulmonary atrioventricular fistula# chronic he!atic disease resulting in
multi!le microvascular fistulas in the lungs$
ulmonary hy!ertension %ith the resulting right,to,left shunt at the atrial# ventricular# or ductal
levels "e.g.# isenmengers syndrome# !ersistent !ulmonary hy!ertension of the ne%born$
Nor)al arterial oxygen aturation (i.e., *eri&+eral Cyanoi! • Increaed deoxygenation in t+e ca&illarie
Circulatory shock
Congestive heart failure 'crocyanosis of ne%borns
et+e)oglo%ine)ia • Congenital )et+e)oglo%ine)ia • Toxic u%tance
(ngestion of %ater high in nitrates
!osure to aniline dye teething gels
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CONSEUENCES AND COMP!"CA#"ONS
Polycythemia
Lo% arterial * content stimulates bone marro% througherythro!oietin release from the kidneys and !roduces an increasednumber of red blood cells.
olycythemia# %ith a resulting increase in oygen,carrying ca!acity#benefits cyanotic children. Ho%ever# %hen the hematocrit reaches253 or higher# a shar! increase in the viscosity of blood occurs# andthe !olycythemic res!onse becomes disadvantageous# !articularly ifthere is congestive heart failure "CH4$.
+ome cyanotic infants have a relative iron deficiency state# %ithnormal or lo%er than normal hemoglobin and hy!ochromia on bloodsmear. ' normal hemoglobin in a cyanotic !atient re!resents arelative anemic state. 'lthough less cyanotic# these infants areusually more sym!tomatic and im!rove %hen iron thera!y raises thehemoglobin.
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Clu$$ing
Caused by soft tissue gro%th under the nail bedas a conse)uence of central cyanosis.
The mechanism for soft tissue gro%th is unclear.
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-y&ot+ei
egakaryocytes !resent in the systemic venous blood may beres!onsible for the change. (n normal !ersons# !latelets are formed
from the cyto!lasm of the megakaryocytes by fragmentation during
their !assage through the !ulmonary circulation. The cyto!lasm of
megakaryocytes contains gro%th factors "e.g.# !latelet,derived gro%th
factor and transforming gro%th factor 6$. (n !atients %ith right,to,leftshunts# megakaryocytes %ith their cyto!lasm may enter the systemic
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Clu$$ing%
Clubbing usually does not occur until a
child is 2 months or older# and it is
seen first and is most !ronounced in
the thumb.
(n the early stage# it a!!ears as shininess
and redness of the fingerti!s. -hen it is fully develo!ed# the fingers and toes become
thick and %ide and have conve nail beds .
Clubbing is also seen in !atients %ith liver
disease or subacute bacterial endocarditisand on a hereditary basis %ithout cyanosis.
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Central Nerou Syte) Co)&lication
&'(rain a$scess
(n the !ast# cyanotic CH7s accounted
for 53 to 103 of all cases of brain abscesses.
8,L intracardiac shunts may by!ass the normally
effective !hagocytic filtering actions of the !ulmonary ca!illarybed. This !redis!osition may also result from the fact that!olycythemia and the conse)uent high viscosity of blood lead to
tissue hy!oia and microinfarction of the brain# %hich are latercom!licated by bacterial coloni9ation.
The triad of sym!toms of brain abscesses are fever# headache# andfocal neurologic deficit.
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)'*ascular stro+e
Caused by emboli9ation arising from thrombus in the cardiac chamberor in the systemic veins may be associated %ith surgery or cardiac
catheteri9ation.
Cerebral venous thrombosis may occur# often in infants younger than
years %ho have cyanosis and relative iron deficiency anemia. '
!ossible e!lanation for these findings is that microcytosis further
eacerbates hy!erviscosity resulting from !olycythemia.
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(leeding Disorders
7isturbances of hemostasis are fre)uently !resent in children %ithsevere cyanosis and !olycythemia.
ost fre)uently noted are thrombocyto!enia and defective !latelet
aggregation.
*ther abnormalities include !rolonged !rothrombin time and !artial
thrombo!lastin time and lo%er levels of fibrinogen and factors : and
:(((.
Clinical manifestations; easy bruising# !etechiae of the skin andmucous membranes# e!istais# and gingival bleeding. 8ed cell
%ithdra%al and re!lacement %ith an e)ual volume of !lasma tend to
correct the hemorrhagic tendency and lo%er blood viscosity.
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Hypo,ic Spells and S-uatting
'lthough most fre)uently seen ininfants %ith tetralogy of 4allot "T*4$#
hy!oic s!ells may occur in infants %ithother congenital heart defects
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Scoliosis
• Children %ith chronic cyanosis#
!articularly girls and !atients
%ith T*4# often have scoliosis.
Hyperuricemia and .out
• Hy!eruricemia and gout tend to
occur in older !atients %ith
uncorrected or inade)uately
re!aired cyanotic heart defects.
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#HAN/ 0OU