NSU- Anesthesia ECG Quiz 6

Conduction block

Any obstruction or delay of the flow of electricity along the normal conduction pathways

Sinus node exit block, AV blocks, and bundle branch blocks

What are the three main types of conduction blocks?

1st degree AV block

Characterized by a delay in conduction at the AV node or sometimes at the bundle of His

-diagnosed by prolonged PR interval >0.2s

-early sign of degenerative disease of conduction system

1st degree AV block

2nd degree AV block

Characterized by dropped ventricular beats

-consistent distance from P to P wave because sinus node is firing normally

-2 types: Mobitz type I and II

2nd degree AV block: Mobitz type I Wenckebach block

Characterized by variable block within the AV node, increasing with each impulse

-each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse fails to make it through

-progressive lengthening of PR interval until one QRS is dropped

2nd degree AV block: Mobitz type I Wenckebach block

2nd degree AV block: Mobitz type II

Due to a block below the AV node at the Bundle of His

-serious - pacemaker is indicated

-greater risk of evolving to complete heart block

-no progressive lengthening of PR interval

-presence of dropped QRS without progressive lengthening of PR interval

2nd degree AV block: Mobitz type II

3rd degree AV block: Complete heart block

No atrial impulses are conducted to the ventricles

-atria and ventricles are driven by separate pacemakers (AV dissociation)

-presence of AV dissociation and ventricular rate < Sinus/ atrial node

3rd degree AV block: Complete heart block

First degree

If the R is far from the P, then you have a _____________

Wenckebach

Loner, longer, longer, drop! Then you have a _______

Mobitz II

If some Ps dont get through, then you have _______

Third degree

If Ps and Qs dont agree, then you have a ________

Bundle branch blocks

Conduction block of current flow in either the right or left bundle branches or both

-diagnosed by looking at width, axis, and configuration of the QRS complexes

Right bundle branch block (RBBB)

-slower depolarization of RV--> wide QRS

-characteristic RSR' (rabbit ears) in V1 and V2

-R' is due to the delayed RV depolarization

-Late RV depolarization causes reciprocal wide/ deep S waves (looks like W) in L lateral leads

Right bundle branch block (RBBB)

Left bundle branch block (LBBB)

-delayed depolarization of LV--> wide QRS

-wide/ notched R waves in lateral leads

-looks like an M

-NO Q WAVES

-reciprocal wide/ deep S waves in V1 and V2

Left bundle branch block (LBBB)

Left bundle branch block (LBBB)

W in V1 and M in V6

Right bundle branch block (RBBB)

M in V1 and W in V6

Hemiblock (incomplete LBBB)

DOES NOT PROLONG THE QRS

-only causes axis deviation

-only diagnosed in the absence of other causes of axis deviation

Left anterior hemiblock

-all current goes down the posterior fascicle

-left axis deviation between -30 and -90 degrees (without other causes of LAD)

-Tall R waves in the L lateral leads

-Deep S waves in inferior leads

Left anterior hemiblock

Left posterior hemiblock

-all current goes down the anterior fascicle

-right axis deviation +90 to +180 degrees (without other causes of RAD)

-Deep A waves in the L lateral leads

-Tall R waves in the inferior leads

Left posterior hemiblock

RBBB + anterior hemiblock

-wide QRS

-RSR' in V1 and V2

-LAD -30 to -90

RBBB + posterior hemiblock

-wide QRS

-RSR' V1 and V2

-RAD

Pacemakers

Used for:

-3rd degree AV block

-development of combinations of AV block and BBB during MI

-recurrent ventricular tachycardias

Demand pacemakers

Most popular, fires when HR falls below a set threshold

Pacemaker electrode placed in single chamber, right atrium

-spike followed by a P wave, normal PRI, normal QRS

Pacemaker electrodes placed in two chambers, right atrium and ventricle

-spike followed by P wave

-spike followed by wide/ bizarre QRS like LBBB

Pacemaker electrode placed in single chamber, right ventricle

-no P wave

-spike followed by wide/ bizarre QRS like LBBB

Risks of pacemakers

-infection/ bleeding

-inducing Vtach or Vfib

-precipitating heart failure

Biventricular pacemakers

Can improve EF and reduce symptoms of heart failure

-used for patients with reduced LV function and/or native LBBB

Bundle branch blocks

Wide QRSs