Amal Mattu gives us a very simple way to distinguish the type of advanced AV block by looking at the PR intervals.

• PR interval gradually increasing = Mobitz I
• PR interval fixed = Mobitz II
• PR interval appears random = 3rd Degree Block

You may also find this link to LITFL on SVT vs VT most informative.

Join in the conversation between Scott Weingart and Steve Smith as they discuss who should go to the cath lab on Dr. Scott Weingart's EMCRIT two part podcast or check out the pdf cheat sheet from Dr. Smith on which patients should go to the cath lab and when to engage you cardiologist for consult.

This is an autosomal dominant disease with variable penetration that is second only to HCM in causing sudden cardiac death in otherwise healthy young people.  Dr. Burns presents basic ECG findings of ARVH as well as discussing other diagnostic studies and treatment.  Highlights below.

 What exactly are the electrical criteria for LVH?  Dr. Burns walks us through it on LITFL.  Not a copa cardiogram, this one's on the house!

Dr. Mattu walks us through a three step method to make identifying heart blocks easy. Just ask three qestions
1) What is the atrium doing? (regular, irregular rate?)
2) What is the ventricle doing? (morphology and thus location? rate?)
3) How are the two related? (Look at PR interval, is it regular? long then dropped QRS, longer, longer then drop? or randomly related? 1st, 2nd, 3rd degree blocks).

Commonly seen after ventricular reperfusion, and generally self limiting, this rhythm is important to recognize as managment with antiarrhythmics is not indicated (and may make the situation worse).  It is a result of a ventricular rhythm that is faster than the atrial rhythm and will generally resolve once the atrial rhythm exceeds the ventricular pacemaker.  Focus on recognizing the underlying causes, treating the cause and not the rhythm, or being watchfully patient as the case may require.  Follow the link to LITFL to learn more.

ECG Features

• Regular rhythm.
• Rate 50-110 bpm. (<50 is likely ventricular escape, > 110 is VT)
• Three or more ventricular complexes.
• QRS complexes >120ms.
• Fusion and capture beats.

The posterior fascicle is much large and less susceptible to injury.  As such it is not likely to occur in isolation, and more commonly seen with some AV node dysfunction as a Bifascicular block (LPFB + RBBB).  Dr, Burns walks us through some of expected ECG findings and also reminds that you should not dx LPFB without first considering more worrisome causes of right axis deviation: PE, TCA overdose, lateral MI, or RVH.  Check out his post on LITFL.

Conduction goes down functioning anterior fascicle, from endocardium to epicardium (initial small voltage) to remaining myocardium from the anterior/superior LV towards the inferior/posterior LV resulting in the following changes:

• Right axis deviation (> +90 degrees)
• Small R waves with deep S waves in leads I and aVL
• Small Q waves with tall R waves in inferior leads (II, III, aVF)

This altered conduction takes longer than usual and the delay can be seen on ECG:

• QRS duration normal or slightly prolonged (80-110ms)
• Prolonged R wave peak time in aVF
• Increased QRS voltage in the limb leads

It helps to remember how the current is conducted.  The posterior fascicle originates inferiorly and posteriorly on the endocardium.  Thus the initial flow of current in LV will be rightward and down, as current moves to the epicardium.  Additionally, depolarization of the right ventricle is progressing normally.  As depolarization progresses, it moves from inferior, posterior to anterior, superior giving you the  patter noted below.  Check out LITFL's page on LAFB.
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• Left axis deviation
• Small q waves with tall R waves in leads I and aVL
• Small r waves with deep S waves in leads II, III, aVF
• QRS duration is normal or slightly prolonged (80-110 ms)
• Prolonged R wave peak time in aVL > 45 ms (measure from start of Q to peak of R)
• Increased QRS voltage in the limb leads

Dr. Burns also provides a beautiful pearl that in LAFB you might see LVH voltage criteria in aVL (R wave height > 11 mm), but there will be no LV strain pattern.

There are several key differences in pediatric ECGs that would otherwise cause alarm in an adult ECG.  Also check out life in the fast lane's page on pediatric ECGs

Axis:  Rightward axis

• Large R wave in V1-V2, small S in V5-V6

Q waves

• Narrow, sharp in inferior and lateral leads

Intervals

• PR short without aberrant conduction
• QRS <80ms prior to age 8
• QT 490ms may be normal up to 6 mo old

T-Waves

• Inverted V1-V3
• usually through age 8, but may persist as 'Juvenile T wave abnormality'

Dr. Mattu reminds us of our differential for really wide QRS complexes, also quick approach to TCA overdose treatment.