Yagel - Fetal Tachyarrhythmias
- = HR >180-200bpm
-Sinus
-SVT
-a-flutter
-VT
-AVRT via AP is #1 cause
-can divide them as:
-atrial tachy = a-flutter, AET
-conduction system tachy = AVRT, PJRT, AVNRT
-VT
-Fetuses: SVT is usually reentrant SVT (70-75%) versus flutter SVT (25-30%); VT very rare
-sustained SVT w 1:1, a-flutter, or VT can --> CHF--> incr RA P, syst vn P, nonimmune hydrops, placental edema, polyhydramnios
-severe polyhydramnios can --> maternal xx = mirror syndrome = Ballantyne syndrome
-maternal hyperdynamic and hypertensive state --> preeclampsia, +/- assoc w placental edema & hydrops
Dx
-can detect by fetal US, CW Doppler, or cardiotocography
-if you can't find a cause to CHF/hydrops, consider paroxysmal SVT
-MMode/Doppler
-DTI is newer technique to Dx...
-Fetal magnetocardiography = magnet that detects fetal electrical activity
Electrophysiological mech of Fetal Tachy
-1:1 AV conduction - likely SVT not flutter
-simultaneous SVC/Ao Doppler --> check VA & AV time to assess RP length and determine if it is short or long RP tachy
-LV inflow/outflow measurements isn't as good bc at HR>160, E & A wave overlap.
-long VA = PJRT or AET
-short VA = orthodromic SVT; very short VA - c/s AVNRT or JET - see very tall atrial & Ao Doppler waves
-PJRT- rarer, via concealed, backward conducting AP w slow AF nd like conduction properties
=AET & PJRT both have HR bn 180-220, while AVRT is usually 220-280
-AET has higher variability in HR
-WPW can be confirmed in 10% of fetuses with SVT
-other preexcitation syndromes - Low-Ganong-Levine synd, and Mahaim syndrome less common
-...
-AET is common in 1-3% of fetuses
-aflutter
... - freq is usually 350-500bpm, w slow fixed or varing ventric rate d/o amt of block.. 2:1, 3:1, 4:1 block...,
-VT - only some case reports, see AV dissoc, ventric rate 180-300bpm
-cant ddx fr JET prenatally
-c/s hypoxia, CM, long QT
Pathophys
-short diastolc--> decr filling--> decr CO, and incr systemic venous volume load & CVP...
-may even --> premature FO closure
-loss of AV synchrony...
-AV vlv regurg
-less coronary filling time bc shortened diastole, incr LVP...
-remodel myocardium --> dilation... tachy induced CM w dilation & hypetrophy
-these can all improve after return to sinus rhythm in some but not all patients
-impaired lymphaatic drainage bc high venous P...
-incr cap leakage, protein loss , change hepatic prtn synth are NOT a big issue in fetuses
Fetal Surveillance
-check for CV/extraCV xx - espec Ebsteins & cardiac tumors
-amniotic fluid amt, placental structure & thickness, hydrops, distribution/extent of fluid accum
-echo/Doppler sonography of veins, check for HF, dilation, AV vlv regurg, etc
-check for DVn pulsation- poor Px if increased,
-repeat fetal HR checks
-fetal breathing & extremity movments
Tx
-Rationale- prevent hydrops/demise
-maternal risk- arrhythmias, except for b-blockers; sinus and AV nd dysfx w Class I-IV drgs and digox, atrial tachy w variable AV block or jctl tachy w digox, Torsades w type Ia and III Rx,VT fr type Ic Rx; also CHF, low K, low Ca, low Mg xx
-fetal risk- arrhythmias...; cant check fetal risk for xx, sudden fetal death shortly p initiation of Rx is reported w flec and sotalol, but most were already hydropic so ? if bc of the Rx
-if intermittent tachy, and fetus near term, maybe only watch off Rx, or c/s digox trial to allow for vag delivery, or early delivery,
-can confirm amt of tachy w a 12-24hr monitor
-early delivery before 34 weeks GA--> more xx, espec if hydropic,
Maternal Surveillance during Rx Tx
-start as inpt
-materlan EKG, exclude WPW, Long QT, myocarditis
-check chemistry and Cr levels, and thyroid levels
-follow ECG in mom...
Fetal Antiarrhythmic Tx Protocols
-bioavailability impacted by pregnancy- intra/extravasc volume, incr FGR, elayed gastric emptying/intestinal transit, decr in plasma protns relative to bld volume; also transplacental crossing varied... bc elevated fetal vn pressure...,
-nearly all antiarrhythm Rx caused dose related placental vssl relaxation, except adenosine caused constriction
-Digox is 1st line for fetal tachy, espec if it is short VA tachy - AVRT,
fetal levels get to 70-100% of mom's if no hydrops. If hydrops, then placental crossing is decr, and hard to get to good levels, also low half life bc incr GFR near term, so need higher dose/loading ds
-need mom's level to be bn 2-2.5ng/mL
-check levels 6-8 hrs after last dose of digox
-amio, flec, verap, quinitinde use will incr digox levels, so must decr the digox maint dose
-start w rapid IV digox load over 48hrs, then change to PO, though if nonhydropic, u can load mom over 6-7 days orally.
-if + hydrops, then other Rx is 1st line, if no hydrops these are 2nd line: flecainide, sotalol, amio +/-digox too
-other Rx no longer used= proc, quin, diospyr, propaf, propran, verap
-flec- class Ic- has good placental passage (~80% of maternal levels achieved), might take 1-14 days to get fetal conversion, most take 4-7 days
-Stoalol - class III- also has bb effect= can have mild negative inotropic effect, good placental crossing - fetus gets 70-100% mom's level
-exclusive renal clearnce, half life 16 hrs, so watch mom's kidneys, watch for ECG xx
-proarrhythmic effect is more prononced in fetus/neonate than adults, so it is 3rd line for hydrpoc fetus w SVT refract to digox, or digox+flec
-if pt has long VA tachy (PJRT, AET) or a-flutter, then class III Rx (stolaol, amio) are indicated
-amio - arrhyth xx...., low placental crossing..., worse if hydrpic, but no negative inotropic effect
-may cause xx fr transient low thyroid xx bc it has iodine--> supress fetal thyroid
-20% will get if p prolonged exposure, so check mom's thyroid levels, and neonates postnatally
-Adenosine- must be given at umbilical vn, limited effect, likely will recur... limited fetal use
-Direct Rx injection to umbilical vn has been done w lots of drugs in refractory cases...; amio would be best bc long half life, but xx of bolus is brady and arrest...
-PJRT often resists Rx Tx but is low enough HR that less xx, Class III Rx- sotalol/amio, and also Ic flec may be used in utero
-persistent VT- amio has worked, or propranolol or flec as 1st line
Effectiveness of Fetal Antiarrhythmic Rx Tx
-see Simpson ref 56
-bn 50-75% of nonhydropic fetal SVT will convert w digox alone (ref 59)
-flec as 2nd line may be successful in most of the rest of cases
-amio also usually successful 2nd line Rx
-if hydropic, digox rarely effective (10-15%) so start w flec or amio
-might combine w digox so you get the digox + inotropic effect
-if severe CM (rare), c/s direct fetal Tx w amio
-this plan will convert ~80% of pts w hydrops
---> fetal mortality if no hydrops is near 0, and 10-20% if +hydrops
-no diff found bn digox for SVT vs aflutter
-aflutter Tx protocol
-similar to SVT
-if paroxysmal, and no hydrops, might just monitor
-if sustained, thencan IV load w digox, then change to Po maint
-digox alone can convert 50% of pts
-likely bc it usually starts after 30 wk GA (2 weeks after SVT usually starts) sustained SVT less dangerous, likely bc heart is more mature, and bc ventric response may be lower; thus starting a 2nd line agent usually not needed. If you start it, it should be in fetus w hydrops- then use stoalol or amio
Postnatal f/u of fetus w tachy
Reentry SVT:
-1/2 may recur postnatally as neonate
-they rec ppx Tx for 6-12months, or at least if they had a postnatal recurrence
-only in 10-20% of infants will have tachy p 1yo, bc the myocardium, conductions syst, annulus fibrous ring all mature
Flutter:
-recurrence rate is higher than reentry SVT
-direct cardioversion postnatally usually fixes it, or can atrial oerdrive pace, or use digox or stoalol
-relapse post conversion to sinus is so rare, no ppx Tx is indicated
AET & PJRT:
-often persist postnatally, long term antiarrhyth may be needed- stoalol, amio, flec
VT:
-class Ic med- flec, propafenone
-propranolol
-amio/sotalol if refractory VT
-if long QT may need pacemaker for a temporary period or longer --> shorten QT and reduce risk of torsades...
Long term outcomes
-most do fine, no prospective eval
-some had PML/hemorrahge likely during fetal hypoxic event...
-even pts w hydrops, most did well if they survived
...