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Assessment of fetal heart function and rhythm
The fetal myocardium
Early Gestation
• Myofibrils 30% of myocytes
• Less sarcoplasmic reticula
Late Gestation
• Myofibrils 60% of myocytes
• Increased force per unit area
• Improved relaxation / contractile ability
Active tension
Passive tension
Gestational changes
• Systolic period stays the same
• Diastolic period gets longer• longer early filling and atrial contraction periods
• Shorter isovolumic relaxation
• LV and RV systolic and diastolic BP increase• No difference between LV and RV in paired
samples
• Atrial pressures don’t change with gestation• LA mean 3.3mmHg, RA mean 3.6mmHg
The fetal circulation
• Oxygenated blood from placenta streams to left heart
• High pulmonary vascular resistance
• Low resistance placental circulation
• Cerebrovascular resistance is autoregulatory
Advantage of fetal circulation
• Parallel rather than series, with (at least) two options for shunting
• If one ventricle fails, re-distribution of blood to the other ventricle is possible in most cases
• This leads to the “one good inlet, one good outlet” rule
•Dysfunction usually only results in poor outcome (“fetal heart failure”) when central venous pressure is elevated
Assessment of fetal cardiac function• Routine
• Heart size and thickness – CTR and qualitative
• Systolic – Qualitative
• Diastolic – Doppler assessment
• Specific *• Myocardiac performance (Tei) index
• Cardiac output
• Specialized / research• Tissue Doppler
• Strain
AHA Guidelines
Cardiothoracic ratio
• Cardiothoracic circumference ratio = 0.45 – 0.50
• Cardiothoracic area ratio = 0.25 – 0.35
Systolic function
• Mainly qualitative
• Shortening fraction (2D or M-mode)
= (end-diastolic−end-systolic ventricular diameter)
end-diastolic dimension
• Cardiac output
Cardiac Output• Combined cardiac output
• both ventricles contribute to systemic perfusion
• CSA x VTI x HR
• Accuracy: • Axial plane PV and AoV
diameters• Axial plane PV and AoV VTI
(small angle of insonation)
• Used for:• High cardiac output states
(anemia, teratoma, AV malformations)
• Low output states (e.g. Heart block, Cardiomyopathy, Ebstein’s)
Routine usage of Doppler
•Assess venous flow•Ventricular inflows, Hepatic vein, Ductus venosus,
UV
•Assess outflow gradients
•Assess MCA and UA PI
Ventricular inflow
• Passive (early) and active (late) filling properties of the ventricle
• A-wave dominant in fetal, becomes more even in later gestation
• Abnormal compliance leads to increased A-dominance.
Hepatic vein Doppler
• Better alignment than IVC, and same waveform unless AV malformation
• Increased a-wave suggestive of• high right atrial pressure
• low ventricular compliance
• atrial contraction against closed AV valve in arrhythmia
• Decreased s-wave suggestive of severe TR
Ductus Venosus
• Follow the UV, look for aliasing
• Saggital view is best for Doppler
• Normal flow is antegrade throughout cycle
• A-wave reversal can be an indicator of placental dysfunction / hypoxia in IUGR babies
• In CHD with expected high RA pressure, A-wave reversal is expected and not associated with poor outcomes (e.g. Tricuspid atresia, Pulmonary atresia)
Umbilical vein and artery• Should be sampled in free loop, as can
vary close to fetus or placenta• Umbilical vein flow should be non-
pulsatile, velocity between 10 and 20cm/s
• UV pulsations usually indicate severely decreased ventricular compliance
• Umbilical artery PI decreases with gestation
• Elevated UA PI indicates• Increased placental resistance• Steal (e.g severe pulmonary
regurgitation, large AVM, vein of Galen)
Middle Cerebral Artery
• Flow to brain under autoregulation
• Low MCA PI = reduced resistance to flow “brain sparing.”
• Suggests reduced total flow AND / OR oxygen content in blood
• Necessitates reduced resistance to maintain nutrient delivery.
• High MCA PI = brain protection from elevated flow
CardiovascularProfileScore
Types of dysfunction – High Cardiac Output• Causes
• Arteriovenous malformations
• Sacrococcygeal teratomas
• Fetal anemia
• Echo Findings• Cardiomegaly
• Dilated RV / LV
• High cardiac output (greater than 625ml/m2 predicts risk of fetal death).
IVC
Sacrococcygealteratoma
Types of dysfunction – High afterload
• Causes• Aortic stenosis (LV)
• Twin-twin transfusion (RV > LV)
• Pulmonary stenosis; Ductal constriction (RV)
• Echo findings• Reduced systolic function
• Reduced inflow time
• Endocardial fibroelastosis
• Abnormal venous Dopplers if both ventricles affected
LVOT Doppler(normal <1m/s)
MV inflow
High afterload
Aortic stenosis Selective IUGR, pulmonary stenosis
Types of dysfunction – intrinsic contractile• Cardiomyopathy: 2.5% of fetal heart disease
• 1/3 Hypertrophic • 2/3 Dilated
• Echocardiographic Findings• HCM
• Myocardial thickness > 2 z-scores above mean• Normal RV / LV diameters• Cardiomegaly
• DCM • Decreased shortening fraction
• Predictors of poor outcome• Uniphasic ventricular inflow• Pulsatile UV flow• Fetal hydrops
Tei index = Isovolumic time
Ejection time
= b – a
a
= 0.70 (NR <0.45)
a
b
Cardiovascular profile score:
• No hydrops = 0
• UV pulsations = -2
• CTR = 0.42 (0.35 – 0.5) = -1
• FS = 0.056 / MR = -2
Total =5
• Combined cardiac output = 192ml/min
• Tei = 0.70
Hepaticvein
Ductusvenosus
UV
Cardiovascular profile score
• No hydrops = 0
• UV pulsations = 0
• CTR = 0.42 (0.35 – 0.5) = -1
• FS = 0.056 / MR = -2
Total =7
• Combined cardiac output
= 240ml/min (50th%)
• RV Tei = 0.8, LV Tei 0.36
Another cardiomyopathy…
• 26 weeks
• Family history of cardiomyopathy
• Non-compaction
• Normal inflows
• No venous Doppler abnormalities
Congenital heart disease
Types of dysfunction – dyssynchrony
• Ebstein’s Anomaly• Atrialized right ventricle
• Volume loading of right (TR)
• Aneurysms
Newer measures of cardiac function• Tissue velocity imaging (TVI) – color or pulse wave
• High frame rates
• Simultaneous velocity measurement in multiple walls
• Angle dependent
• Strain imaging• Need high frame rates
Fetal arrhythmia
Fetal Arrhythmias: Background
• Incidence
• Effects 2% of the pregnancies
• Accounts for 10-20% of referrals for fetal echo
• Risk factors
• Assessment• Rhythm (irregular vs regular)
• Rate (fast vs slow
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Arrhythmia: Types
• Ectopy• Premature atrial contractions (PAC)• Junctional ectopic beats• Premature ventricular contractions (PVC)
• Tachycardia• Sinus tachycardia (HR 180-200 bpm)• Supraventricular (ectopic atrial tachycardia, AV reentry tachycardia and
permanent junctional reciprocating tachycardia)• Atrial Flutter (HR 300-550 bpm due to AV block)• Junctional ectopic tachycardia• Ventricular tachycardia
• Bradycardia• Sinus bradycardia (HR 90-110 bpm)• Premature atrial beats with AV block• Congenital heart block (1st not associated with bradycardia, 2nd and 3rd
degree)
University of Alberta Fetal and Neonatal Cardiology Program
Difficult to differentiate
Difficult to differentiate
Fetal Tachycardias: Risk factors
• Usually no identified risk factors
• Maternal conditions
• Maternal Beta-stimulation
• Thyroid-stimulating antibodies
• Fetal conditions
• Severe RA enlargement • Ebstein’s anomaly, tricuspid dysplasia, RA aneurysm
• Cardiac tumors
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Bradycardias: Risk Factors
Maternal conditions:
• Auto-immune antibodies (Lupus, Sjogren’s) – 1st, 2nd, CHB.
• Exposure to medication (i.e. beta-blocker)
Fetal conditions:
• Long QT syndrome – sinus bradycardia / torsades
• Left atrial isomerism – sinus bradycardia / complete block
• Fetal L-TGA – complete heart block
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Arrhythmias: Making a Diagnosis
Fetal echocardiogram-inferences based on mechanical atrial and ventricular events
• Blood-flow• PW Doppler LV inflow-outflow• PW Doppler SVC-Ao flow• PW Doppler pulmonary branch artery-vein
• Muscular movement• M-mode (cursor through the atrium and ventricle)• Tissue Doppler Imaging
Fetal ECGFetal magnetocardiogram
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Arrhythmias: Making a Diagnosis
University of Alberta Fetal and Neonatal Cardiology Program
PW Doppler: pulmonary vein/arteryPW Doppler: LV inflow/outflow
PW Doppler: SVC - Ao flowM-mode: Left atrium - right ventricle
Pulm vein flow
PA flowinflow
outflow
A A A A A A
V V V V V V
• Mechanical PR interval
University of Alberta Fetal and Neonatal Cardiology Program
SVC
Ao
PW Doppler: SVC – AO PW Doppler: LV inflow/outflow
AV
AV
A
V
Fetal Arrhythmias: Making a Diagnosis
Fetal Arrhythmias: Types• Ectopy
• Premature atrial contractions (PAC)• Junctional ectopic beats• Premature ventricular contractions (PVC)
• Tachycardia• Sinus tachycardia (HR 180-200 bpm)• Supraventricular (EAT, AVRT and PJRT)• Atrial Flutter (HR 300-550 bpm)• Junctional ectopic tachycardia• Ventricular tachycardia
• Bradycardia• Sinus bradycardia (HR 90-110 bpm)• Premature atrial beats with AV block• Congenital heart block (1st, 2nd and complete)
University of Alberta Fetal and Neonatal Cardiology Program
Difficult to differentiate
Difficult to differentiate
Fetal Arrhythmias: Ectopy
• Premature atrial contractions (PAC)• Incidence: 5% of all pregnancies >30 weeks
• Benign in 98%; ~ 2% will trigger/be associated with intermittent SVT or atrial flutter
• Associated with CHD in 1-10% cases
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Ectopy: PACs
University of Alberta Fetal and Neonatal Cardiology Program
V V V V V V V
A PAC A PAC A PAC A PAC
V
V
A PAC
V
A PAC
Conducted PACs
Blocked PACs
Fetal Ectopy: PVCs
• Premature ventricular contractions (PVC)• PVCs are 10x less common than PACs
• PVCs can be associated with VT
• Difficult to differentiate from junctional ectopic beats without an ECG
• Associated with • cardiomyopathies
• myocarditis
• intracardiac tumors
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Ectopy: PVCs
University of Alberta Fetal and Neonatal Cardiology Program
X
V V V V V V
A A A A A A
X
2X
Tachycardia• Sinus tachycardia (HR 180-200 bpm)• Supraventricular (SVT)
• Ectopic atrial tachycardia (EAT)• Atrioventricular re-entry tachycardia
(AVRT)• Permanent junctional re-entry tachycardia
(PJRT)• Atrial Flutter (HR 300-550 bpm)• Junctional ectopic tachycardia• Ventricular tachycardia
• Bradycardia• Sinus bradycardia (HR 90-110 bpm)
• Premature atrial beats with AV block
• Congenital heart block (1st, 2nd and complete)
University of Alberta Fetal and Neonatal Cardiology Program
Difficult to differentiate
Difficult to differentiate
Fetal Arrhythmias: Types
Fetal Tachycardias: SVT
• SVT • Most common fetal tachycardia (66-90%)
• Usually 1:1 A-V conduction
• Includes: AVRT, EAT and PJRT
• Nonimmune hydrops in 40-50% (older series) and 20-25% (recent series) which increases risk of fetal and neonatal demise even with treatment (with successful treatement <10%)
• Hydrops is associated with slower response to therapy and need for more than 1 medication
• Hydropic mechanism:
•
University of Alberta Fetal and Neonatal Cardiology Program
⬇ ventricular compliance of
the fetus
⬆ atrial and ventricular filling
pressures
⬇ filling time⬆ pressure
through the venous system
⬆ transudativeforces
⬆ cell and tissue edema
A A A A A
VVVVV
250 ms
Fetal Tachycardias: SVTLV inflow/outflow• Short AV-long VA
relationship = EAT
SVC-AO flow• Long AV-short VA relationship=
AVRT
University of Alberta Fetal and Neonatal Cardiology Program
Long AV interval (133ms)
short AV interval (75ms)
• Atrial flutter• 20-25% of fetal
tachycardias
• Rate~300-550bpm
• AV conduction (2:1; 3:1)
• > 27 weeks
• Hydrops ~13%
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Tachycardias: Atrial Flutter
• Rare
• HR ranges between 170-400bpm
• Intermittent runs
• Complete A-V dissociation• Exception: retrograde conduction through the AV node = 1:1 conduction
• Associated with long QT syndrome • suspect if intermittently bradycardic
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Tachycardias: V Tachycardia/JET
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Tachycardias: V Tachycardia/JET
A A A A A A
V V V V V V V
o 1:1 conduction
o Rate 180-200 bpm
o AV dissociation
o Ventricular rate~ 210 bpm
• Ectopy• Premature atrial contractions (PAC)• Junctional ectopic beats• Premature ventricular contractions (PVC)
• Tachycardia• Sinus tachycardia (HR 180-200 bpm)• Supraventricular (EAT, AVRT and PJRT)• Atrial Flutter (HR 300-550 bpm)• Junctional ectopic tachycardia• Ventricular tachycardia
Bradycardia• Sinus bradycardia (HR 90-110 bpm)• Premature atrial beats with AV block• Congenital heart block (1st, 2nd and complete)
University of Alberta Fetal and Neonatal Cardiology Program
Difficult to differentiate
Difficult to differentiate
Fetal Arrhythmias:Types
• Sinus bradycardia• 1:1 AV conduction
• If transient, is benign
• Persistently low HR:• Blocked PACs - common!
• Fetal distress usually gradual
• Long QT syndrome
• Structural CHD• Left atrial isomerism
• L-TGA
University of Alberta Fetal and Neonatal Cardiology Program
A A
V V
A
V
A
V
Fetal Bradycardias
Fetal Bradycardias: AV Block
10 AVBoLong A-V interval
20 AVB; Mobitz IoA-V interval progressively
increases, then drops conduction
University of Alberta Fetal and Neonatal Cardiology Program
20 AVB; Mobitz IoA-A interval regular
oA-V dissociation
Complete AVBoA-V dissociationoVentricular rate:60-70
bpmo47% structural CHDo47% maternal antibodies
University of Alberta Fetal and Neonatal Cardiology Program
Fetal Bradycardias: AV Block
Questions?