assessment of fetal heart function and rhythmpedsecho.ca/data/documents/fetal-function.pdf · •lv...

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)


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


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


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




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


SVC

Ao

PW Doppler: SVC – AO PW Doppler: LV inflow/outflow

AV

AV

A

V


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)




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


Fetal Ectopy: PACs


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


Fetal Ectopy: PVCs


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)




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:

•


⬇ 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


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%


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


Fetal Tachycardias: V Tachycardia/JET


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)




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


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


20 AVB; Mobitz IoA-A interval regular

oA-V dissociation

Complete AVBoA-V dissociationoVentricular rate:60-70

bpmo47% structural CHDo47% maternal antibodies


Fetal Bradycardias: AV Block

Questions?

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