-may be an intrinsic or extrinsic cause
-First degree AV Block- nearly always due to abNl conduction in atrium or AV Nd (as oppose to something more downstream)
-transient prolongation, or failure of AV conduction- can be bc of concealed conduction of atrial, jctl, or ventric extraystoles (???)
-Second degree AV Block- occurs w/in AVN & HPS or at ventricles
-AVN conduction influenced by symp/parasymp balance; as infant symp outweighs para...
-HPS less influenced by autonomic nervous system
-Long PR in context of bradycardia- likely due to vagal tone
-Long PR in context of Nl rate- likely AV nd dysfx
-Functional 1st & 2nd AV Block- seen w rapid atrial pacing- unlike w sinus tachy, there's no sympathetic enhancement of the AVN so it blocks rather than conducts...
-Pt at high risk for AV Block:
-L-TGA, several auto dom genetics..., a block in HPS rather than AVN is more likely to become complete HB
ECG
-1st Degree AVB
-due to AVN xx
-PR above Nl for age
-1:1 AV conduction is maintained
-PR decreases as rate increases
-does not progress to higher block
-w exercise, the PR will normalize bc w/draw parasymp stim
-2nd Degree AVB
-see a pattern of dropped beats- e.g. every 3rd beat etc; so characterize it by P:R ratio (3:2, 4:2)
-must DDx regular PACs that are not conducted- these would cause irregular PP interval (bc early PAC) & the P wave would be diff morph
-Mobitz I = Wenckebach
-gradual PR prolongation then drop the beat
--> greatest PR is just before the nonconducted P wave
--> the RR interval after the missed beat is shorter bc PR is shorter...
-Atypical Wenckebach = when it occurs w sinus arrhythmia, and w longer runs of conducted beats bn blocked beats, is more common than the typical form.
-Mobitz II
-no PR variation, just drop a beat suddenly
-RR interval is thus constant bc PR interval doesnt change...--> RR of nonconducted interval is 2x that of the conducted RR....
-2:1 AV Block
-every other beat conducted- cannot DDx Mobitz I vs II
-Long QT syndrome can present as 2:1 AV Block
-bc mutation of K+ ion ch (LQTS1)--> delayed repol, so still in ERP w next P, = poor Px...
-Advanced AV Block
-2 or more P waves are not conducted, but no true 3rd degree AV Block; may progress to CAVB.
EP Study
-not usually indicated
-but, would show prolonged AH w slow intra atrial or AV ndl conduction if 1st degree AVB
-same w Mobitz I- long AH bc it is usually an intra AVN problem
-w Mobitz II--> infranodal xx so --> Nl AH, but nonconduction to ventricles from His
-1st AVB & 2nd Mobitz I have prolonged ERP and fxl RP for atrium & AV Nd
Px/Tx
-Most 1st/2nd AVB don't progress to 3rd AVB, so most dont need Tx
-seen on Holters of healthy teens/adults, espec athletes at night who have sympathetic w/drawal
-rec avoiding Rx that slow AVN conduction
-rare to get Sx fr 2nd AVB
-can give atropine, isoproterenol, temporary pacing
-Lyme carditis can cause AVB but then completely resolve w time
-no ch Rx for signif AV block; may need permanent pacing
(e.g. for LQTS w 2:1, NKX2.5mutation, etc
Complete Heart Block - Third Degree Heart Block
Epi
-congenital HB- 1/15-22k live newborns
Etiology
-congenital HB
-neonatal Lupus -->s 60-90% of it unless +CHD
-maternal Ab crosses placenta in 1st tri
-myocarditis, structural cardiac dz- ccTGA, AV discordance, polysplenia w AVSD
-Genetics- Kearns-Sayre syndrome
-see fibrous tissue replacing AV nd/surrounding tissue, or bc of interruption bn atrial myocard & AVN
-absence of AVN
Neonatal Lupus
-Complete HB, hepatobiliary dz, malar rash, low pltlt, +/- myocarditis
-often presents as Complete HB
-transplacental maternal anti-Ro/SSA and/or anti-La/SSB Ab
-2% of SLE mom's will have affected fetus
-if has prior +child, then 15% chance next child will have it
-additional 6% have isolated rash but no CHB
-the Ag's are on surface of myocardium during GA 18-24 as apoptosis occurs--> Ab binds it and releases TNF--> fibrosis; & the Ab inhibs L and T type Ca Ch activation, needed for AVN conduction
-4% pts get SA nd xx too, w sinus brady, but not permanent usually
Sx
-d/o etiology & age of presentation
-In Utero Presentation
-fetal brady at 18-28 week GA, 95% are bc of SLE, w +maternal serum Ab,
--> fetal hydrops, myocarditis, EFE, spont intrauterine demise, pericardial effusion,
-in utero 2nd degree AVB can progress to CHB
-if survive to delivery, still high neonatal mortality, 9-27% per some small studies, incr if <34wk GA
-Neonatal Presentation
-cannon a waves at neck, first heart sound varies in intensity, intermittent gallop & murur
-90% neonates w CHB are due to SLE
-atrial rate up to 150s w ventric rae <50 --> high risk
-1st & 2nd HB as neonate can progress to CHB (!)
-outcome better if postnatal Dx vs prenatal
-Childhood Presentation
-40% of congen HB don't present until childhood- mean 5-6yo
-p/w slow heart rate or syncope; only 5% these pts have SLE as cause
-may initially be intermittent, then get more permanent
-Sx- reduced exercise tolerence, presync/syncope, sudden death also seen,
-Other causes (rare in kids):
-Febrosis/Sclerosis
-Lenegre's dz & Lev's dz
-Familial AV block
-Valvar Dz- Ca'ion & fibrosis of Ao or MV rings, extending into conduction syst
-CM- HOCM, amyloidosis, sarcoidosis
-Hyperthyroidism, myxedema, throtoxic peroidic paralysis
-Neuromusc heredodegen dz, dermatomyositis, rh dz, Paget's dz
-Infections- mycarditis fr rh fever, dophteria, viral, SLE, toxo, bact endocard, syph, Lymes
-CA- Hodgkins, other lymphomas, multiple myeloma, cardiac tumors
-Rx- a bunch can block it...
-Ischemic heart dz
Tx
-In Utero Tx- if SLE- steroids in utero; isoproteronal or pacemaker immediately post partum
-by 20yo, 11% neonatal, 12% childhood CHB need pacer; 90% by 60 in one report...
Pacemaker Indications (must taylor to your child)
Class I
-Sx brady- sync/presync
-Mod-Much exercise intol
-HF due to brady
-LV dysfx or low CO
-wide QRS escape rhythm or block below His bundle
-Complex ventric arrhythm
-infant w ventric rate <50-55bpm, or <70bpm if +CHD
-sustained pause dependent VT, +/- prolonged QT, in which efficacy of pacing is documented
-Advanced 2nd/3rd AVB lasting 7 or more days post-op
Class II
-2nd/3rd HB within His bundle, in ASx pt
-Prolonged subsidiary pacemaker recovery time w pause >3 seconds
-Transient surgical 2nd/3rd HB that reverts to bifascicular block
-ASx 2nd/3rd AV block and a ventric rate <50bpm when awake beyond 1yo
-Complete AV Block w double or triple rest cycle length pauses or minimum HR variability
-ASx neonate w congen CHB and brady
-Long QT synd, espec if ventric arrhyth
-Congen hrt dz, and impaired hemodynamics due to sinus brady or loss of AV sync
-Neuromusc dz w any AV block (1st degree too!), with/without Sx - bc may have unpredictable progression to 3rd AVB (!)
Px
-w neonatal/in utero- much early mortality - in 2 reports total of 17% died in utero or by 3mo
-ASx infants usually stay ASx until childhood/teen/adult
-if baseline HR <50 in kids, and unstable jctl escape--> c/s early pacing
-torsades is a risk of AV block and ventricular bradycardia
-if ASx and no syncope, might still et xx- the ventric rate falls slowly as pt ages, and to compensate for the brady the heart enlarges--> higher SV, but can --> LV enlargement by voltage criteria, and ST-T changes; --> hrt failure possibly
-Great Px if get pacer
-though still at higher risk of HF
-in a study of neonatal lupus pts, still got hypertrophy and insterstitial fibrosis in some, then HF, and eventual OHT in some; some get DCM- 6% by 6-7yrs old in one series of lupus pts
-long term RV pacing can --> ventric async and HF
-biventric pacing once pt big enough may be good