Yagel - Fetal Bradydysrhythmias

Fetal Bradycardia Yagel32

Dx

-use Doppler/MMode

-line across atrial/ventric wall or inflow/outflow

-AV contraction time interval ~ = electrical PR interval

-Nl range in fetus is 95-140msec, d/o HR & GA

Path

-slow atrial pacemaker w Nl 1:1 AV conduction

-Heart block at AV hct

--> decr CO, espec if assoc structrual CHD

-reduced compliance of Nl fetal heart--> diastolic filling d/o atrial contraction more than postnatally, so need AV synchrony...

-HR <50bpm and dissoc of AV contractions --> worst xx

Presentation

-sinus brady (<100bpm) can occur frequently in short bursts, and are Nl - bc of incr in vagal tone, or bc pressure on abd fr the transducer. recovery is within seconds or so.

-Sustained sinus brady - should check for other xx that is causing fetal illness- can be sign of impending fetal demise, decr fetal mvmt, or fetal distress

-Sinus nd dysfx (can't dx prenatally), maternal hypothermia (can occur fr Tx w Mg for premie labor)

-Long QT syndrome- incr risk of malignant VT...

-of fetuses w long QT and HR bn 70-100bpm, fetus might have 2nd degree AVB too, bc of delayed ventricular repolarization

-check for FHx

-Atrial bigeminy with blocked PACs can --> moderate brady --> HR 60-80bpm

-if every 3rd beat is blocked, then --> irregular ventric rate, not as slow -HR 80-110

-Use MMode to DDx blocked PACs with 2:1 conduction from 2nd degree aV block

-blocked PACs are well tolerated, no Tx needed usually. But must Dx it so OB doesn't confuse it for fetal distress.

-Familial Idiopathic a-fib with slow ventricular response- very rare

-auto dom, male>female, also seen in kids/teens

-good Px

-Bradycardia with Jctl or Ventric Escape betas, or 2nd Degree AV block

-2nd degree AV block - not able to Dx well prenatally; ID it w MMode of atrium and ventricle, and see regular 2:1 conduction; but hard to DDx it from complete AV block with a ventric escape that is 1/2 that of the atrial rate..., the apparent AV synchronization can last for long periods of time in the setting of AV block (isochronicity is maintained).

-Also look for Mobitz I (Wenckebach) - AV interval increases until dropped beat...

Complete Heart Block

-uncommon - 1/20,000 newborns, but higher prenatally since some fetal demise

-Isolated Complete HB

-due to AI cause usually- Maternal CT dz- Sjogrens/SLE, often ASx mom, w + auto Ab for anti-SSA/Ro, or anti-SSB/La Ab --> react to fetal tissue --> AI injury --> harm AV nd

-of women with known anti-SSA/B, there is only a 2-5% risk of a child w complete HB; if she had one with complete HB, still only a 15-20% that another child will get it

-starts 18-24 weeks GA, progress from 2nd degree to 3rd degree in some pts

-~75% of fetusses with isolated compelte HB survive to beyond the neonatal period, and almost all of them did not get hydrops.

-a ventric rate of <55bpm --> poor Px, as does decr fx, or EFE

-Complete HB assoc w structural Heart Dz

-LA isomerism, discordant AV connections --> worse Px

-also some reports of assoc w LVNC

-30% of newborn pts w complete HB have assoc structural heart dz

-a high rate of fetal loss if assoc structural dz..., in one study 15% of CHB+structural dz had demise by end of neonatal pd. Half of the survivors had AV discordance; Px is worse if +hydrops or ventric rate <55bpm

Prevention & Prenatal Tx of CHB

-?need to Tx if most survive - if there is CHF/hydrops, then Px is worse

-1st degree HB may preceed worse HB, so early Tx might prevent progression (?)

-Tx HF with hydrops - Digoxin and Lasix adm transplacentally or directly into umbilical vein

-has resovled fluid accum in some pts, but failed in others espec if assoc structural hrt dz

-Tx AI xx with glucocorticoids to stop inflmn- some have--> resolve fetal effusions w prednisone or betamethasone, though HB persisted

-Dexamethasone in one study showed improved hydrops and improved HB

-Prophylactic steroids +/- plastmapheresis has been proposed for anti-SSA/SSB + women;

-Floruinated steroids = Dexameth & betameth, cross placenta better, might be considered for fetuses w imcomplete HB & "commencing hydrops". - but it did not show improvement in degree of CHB

-Tx w sympathomimetic Rx to incr HR to >50-55bpm bc outcomes are better if >50bpm

-Terbutaline & salbutamol cross placenta well, may --> 15-25% incr in fetal HR

-maternal Isoprenaline infusion didnt' change fetal HR, likely doesnt cross placenta well

-might consider transplacental admin of salbutamol

-MUST exclude long QT w 2:1 AV block prior to giving symp Rx, which could worsen it...

-Experiments being done w prenatal pacing- good animal results, failed in humans so far, might be better to delivery prematurely and then pace...