Heart Block- First, Second, & Third Degree Dick14-15

-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