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Fetal Echocardiography
Fetal Echocardiography
Indications
-maternal dz
-teratogen exposure
-FHx of CHD or assoc syndromes
-OB US suggesting cardiac/extracardiac dz (chrom xx)
Timing
-Usually 2nd tri - 17-23 weeks - ~time as OB US, and before time period for termination of PG
-Late 1st trimester increasing in the wake of better transvag US
-3rd trimester/late 2nd if repeat OB US concerning
Technique
-need special probe
-best images w high-freq transducer: 6-10MHz w dynamic focusing capability
-set frame averaging option to off or low
-compress setting allowing for narrow dynamic range (grayscale) --> better Sn to define blood-tissue interfaces
-Image quality can be decr bc of thick maternal abd wall, fetal bones; but amniotic fluid helps
-Lower freq transducer, and use of harmonic imaging can help in 3rd tri pt if greater distance to fetus
-High freq, high res endovaginal transducer for late 1st tri PG may be needed
Screening Fetal Echo
Components:
2D
-Orientation to fetal position
-Exclude obvious fetal hydropes - check pl effusion, pericard effusion, ascites, skin edema
-Visceral/atrial situs check
-Cross Sectional Imaging
-Cardiac Axis
-Cardiac Size/CT ratio
-Cardiac Position
-LA, RA
-Atrial Septum
-P Vns- at least 1 R & 1 L
-TV, MV
-RV morph, LV morph
-Ventricular Septum anatomy
-LVOT, Ao, PA, RVOT
-3 Vessel View Sweeps
-3 vessel view- Nl GA position, size relationship
-Branch PAs
-DA orientation, size
-Ao Arch orientation, size
-Trachea
-L Innom Vn
-Sagittal Sweeps
-R SVC, R IVC
-LA, RA
-Atrial septal anatomy
-Ao arch
-Ductal arch
-TV, MV en face
-RV, LV morph
-Ao/PA Outflow
-Basic RV, LV syst fx
-Ductus Venosus, Umbilical Artery, Umbilical Vein Anatomy
Color
-TV, MV
-Ventric Outflow
-P Vns
-Ao Arch
-DA Arch
-IVC
-DV
-UA, UV
Pulsed Doppler
-Ventric Inflows & outflows
-DA
-Ao Arch/isthmus
-P Vns
-IVC/Hepatic Vn
-DV
-UA, UV
Rhythm Check
-Fetal HR
-Relationship bn A and V contractions
2D:
-Cross-sectional, sagittal, coronal images thru the fetus chest
-Short & LLong axis of fetal heart
-Lungs are filled w fluid--> able to see heart-lung relationship well
Visceral/Atrial Situs
-must orient to fetal position- it's hard!
-transducer at fetal sagittal plane = long axis --> image the spine, head, legs at lower magnification --> ID's fetal position
-w fetus supine or prone, if vertex or breech, can orient transducer mark twd fetal head along the long axis of the fetal body, an then rotate 90 degr clockwise--> cross sectional image that shows fetal L on the right of the screen if pt is supine; reverse if prone...
-this is harder if pt is lying transverse.
-Then, get cross sectional images starting at abdomen, and sweep to chest to check visceral/atrial situs
-R dominant liver, L sided stomach/spleen, R IVC --> c/s visceral situs solitus
-Sweep to chest, see IVC moves ant to connect to floor of RA, just beneath septum primum and the path to the FO
-Cross section thru fetal chest--> 4Ch heart view
-Heart size- should be 1/3 size of fetal chest
-Cardiac Axis- axis of ventric septum relative to midline of fetal chest- usually at 43+/-7 degrees
-RA and part of RV is R of midline
-LA, LV, and part of RV is L of midline
-if not Nl, c/s xx - unilat lung hypoplasia, CDH, pulm sequestrtion/cystic adenomatous malfrmn
-LA is most posterior chamber, just ant to desc Ao
-ensure at least 1 L and 1 R P Vn to LA, w L PVn coursing closes to L Desc Ao- use color & PW
-Atrial Septum- ensure check septum primum & secundum, and FO
-sweep post/inf fr 4Ch view, see thin coronary sinus course thru LA just behind inf-post ring of MV
-Check for CS dilation- DDx fr an ASD at it's mouth into the RA; c/s L SVC
-MV and TV on 4Ch & short axis planes- see offset of valves, w septal leaf of TV more apically displaced than MV ant leaflet
-short axis image thru inflow part of AV vlvs --> check AV vlv morph
-RV vs LV:
-Prenatally, the trabeculations are not as diff bn RV and LV. If Nl AV vlvs, they can help DDx which ventricle is L vs R
-RV more pyramidal shape, has moderator band
-LV more pullet shaped, w 2 pap muscles, best seen in short axis or sagittal sweep
-see continuity bn ant MV leaflet and semilunar (usually Ao) vlv... usually...
-Ventricular Septal Anatomy
-check anatomy w cross sectional sweeps thru chest fr heart's crux just above the diaph to the ventricular outlets; or sagittal sweep fr R aspect of hrt then going leftward
-check inlet, membranous, trabecular, and outlet parts
-Sweep w color Doppler at low velocity to detect small VSDs
-Ventricular Outflow tract & GAs
-sweep fr head in a 4Ch view
-LVOT starts more post and L relative to RVOT and goes rightward
-RVOT starts more ant & goes L ward, wrapping arnd the LVOT, then joining PA, which is L of midline
-3 Vessel View- to check Nl/AbNl GA anatomy, arches, and airway
= cross section image thru superior mediastinum, that in Nl fetus shows R SVC, Asc Ao, MPA
-MPA- seen in long axis, is the most ant & leftward vessel
-Asc Ao- seen in short axis, is R and slightly post
-R SVC- seen in short axis, more R and post, w the smallest diameter
-if abNl, c/s R hrt obstruction, AR/PR, interr IVC w azygous continuoation, vein of Galen anuerysm
-see RPA going behind Asc Ao and SVC
-to see LPA, rotate slightly fr a straight cross sectional plane, following it as it goes under DA
-See MPA joining DA as the DA goes back, just L of midline to meet the desc Ao
-Sweep twd head, and see Ao arch going fr R ant to L post, crossing midline twd the L of the trachea and then joining the desc Ao. ==> confirms that Ao/ductal arches are L sided
-If fetus supine, rotate 90 degr along the plane of asc Ao (fr R ant to L post) --> long axis view of Ao Arch. See Asc Ao starting more central, then goes ant and curves postly to meet the desc Ao, & gives rise to 3 brachiocephalic arteries. DDx the canelike look of the Ao vs the hockey stick shape of Desc Ao
-See L & R heart are symmetric at early GA, espec b4 16 wks GA, then RA, RV, MPA, DA are a bit larger then L sided structures. If too much, or if reverse is true, then c/s L or R heart obst lesion...
Doppler:
-ensure narrow sample volume, low velocity settings
-used mainly to confirm dx made by 2D
-routine doppler of ventric inflow/outflow, PVn, Ao/DA, IVC/DV, UV/UA is good to show Nl & ID AbNl...
Fetal Heart Function:
-Check heart size, CT ratio, wall thickness, IVC diam, fetal HR, hydrops presence
-Check Systolic fx- check SF by 2D/MM - LV & RV SF Nl = 34+/-3%; Simpson's biplane not reproducible
-Check SV & CO- from 2nd tri to term, SV & CO is less in LV than RV
-Check Diastolic fx- PW thru ventric inflow, IVC, DC, UV
-Nl developmental diastolic changes will affect the LV/RV inflow pattern w an incr E wave velocity during early diastole, with minimal changes to the A wave velocity <-- bc of progressively better relaxation & compliance of the ventricles
-Check simultaneous LV inflow & outflow --> assess LV isovol relax time - Nl for pt p 20wk GA = 43+/-8msec (corrected for HR)
-Check Tei Index aka Myocardial Performance Index- global fx: Tei = (Isovol relax time + Isovol contractn time)/(Ejection time). Check for RV & LV. Nly decreases w GA during 2nd & 3rd tri, with LV MPI dropping more than RV MPI
-Doppler imaging- ~new- strain, strain rate etc - should stay same regardless of GA and regardless of HR; tissue velocities (TDI) increase w GA.
Fetal Rhythm Assessment:
-MM or PW - check mechanical events of atrial & ventric contraction- w wall motion or w flow
-via simultaneous LV inflow and outflow; PA and PVn; SVC and Asc Ao interrogations
Fetal Cardiovascular Pathology
Structural Heart Disease:
-Check AV, VA connection; Ao, DA position, morph, flow
-can miss small/mod VSD/ASD, minor valve abNlies, complex apical muscular defecties, PAPVR, cor art anom
-Note that early mild MV/SL obstruction initially may progress thru pregnancy,
-Bad AS/PS can --> ventric hypertrophy, and eventually retrograde ductal/Ao Q if critical obst--> need PGE postnatally.
-if sev obst early --> ventric failure & EFE; sev AS may --> shunt L to R at PFO. Fetus can still thrive as long as the other side can support the excess flow, but there is usually still progressive hypoplasia of the ipsilateral ventricle, AV vlv and GA.
-sev L heart obst, w progressive restriction of FO --> postnatal sev LA hypertension, cyanosis, pulm edema
-see thickened atrial septum, small ASD, turbulant Q at AS; check PVn PW--> incr flow reversal in atrial systole and decr early diastolic forward flow (--> to and fro flow)
-Ventricular aneurysms & diverticuli more common prenatally bc might not be compatible w birth
-restrictive FO, DA constriction, DV agenesis may --> CV xx and only Tx would be delivery when viable
Fetal Heart Failure
-Umbilical Venous return- provides O2 bld fr blacenta thru ductus venosus (mainly) and then across FO
-needs low downstream systemic venous, atrial, ventric filling P
-any xx that increases CVP can --> xx --> hydrops, poor umbilical Q w hypoxemia--> demise
-Must have at least 1 patent & competent AV and SL vlv, a Nly filling and ejecting ventricle, and well fx placenta
-HF--> hydrops- pl/pc effusion, ascites, skin edema
-usually bc 1y myocardial or structural dz that affects both ventricles; bradyarrhythmias/tachyarrhythmias that affect filling/ejection, or extracardiac xx that --> incr CO
-Primary Myocardial dz- syst and diast fx might be xx, w diast fx most assoc w the evolution of fetal HF
-PW of ventric inflow, IC, D, UV can assess severity of the altered CVP and likelihood to --> hydrops
-AbNl systemic vns Doppler - can DDx cardiac fr non cardiac hydrops etiology
-Sev TR is very poorly tolerated- see big RA, RV; which worsens the TR more, then RV unable to generate enough P to open the PVin systole; +/- PR, which worsens the RV vol OD. Initialy resdistrib Q to L side, but that eventually affects L heart too; --> incr CVP, and hydrops. The ng LV filling and reduced LV CO--> fetus less able to respond to acute physio changes --> sudden demise, espec in 3rd tri. SVT may be assoc, and --> decr filling even more at LV
Fetal Arrythmias
- >90% of fetal arrhythmias are found to have no arrhythmia at the time of fetal echo, or just PACs
-Use of Doppler & MM
-If PACs w AV Block in bigemony then can --> fetal brady
-Tachyarrhythmias- SVT, A flutter, JET, VT
-check relationship of a and v contractions, mode of onset and offset, atrial and ventric rates for Dx
-Most common fetal tachy is SVT w 1:1 AV contraction
-SVT: Short and long VA types
-w simultaneous Doppler at SVC and Asc Ao, check the AV and VA time intervals:
-AV > VA = Short VA SVT- reentrant tachy assoc w accessory pathway
-AV <VA = Long VA SVT- sinus tachy, EAT, PJRT
-A flutter = 2nd most common type of SVT--> a rate of 350-500bpm, w variable AV conduction
-VT & JET --> rapid ventric rate w no VA synchrony (hard to DDx bn the 2 bc no ECG)
-Bradyarrhythmias-
-Dx w ventric rate <110bpm
-Sinus Brady = #1, can occur intermittently during an exam, should resolve quickly...
-Persistent Fetal Sinus Brady - c/s diffuse systemic dz/distress
-Persistent fetal brady w ventric rate 35-120 may be bc of 2nd/3rd AVB
-may be seen w structural hrt dz- LA isom/polysplenia synd, lesions assoc w L ventric looping
-in isolation, often bc of maternal anti-Ro or anti-LA auto-Ab
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