Heart Block - in degrees...

The heart is a pretty sophisticated bit of equipment, which doesn't stop it from fouling up in many various and irritating ways. Here are some of them.

Heart Block
"interference of the conduction process"


First Degree
Prolonged PR Interval

Causes:
Normal variant/acute MI/CAD/acute rheumatic carditis/digoxin toxy/electrolyte distub.

No Tx


Second Degree
Three types
Intermittent failure of conduction

• Mobitz Type 1 - "Wenckebach"

Progressive prolonging of PR, then complete failure of conduction, then conducted beat with shorter PR interval. Cycle which repeats. Imagine a wonky cycle that gets harder and harder to pedal, until you fall off, and then you hurriedly get back on and start all over again.
Benign. No Tx.

• Mobitz Type II

Occasional failure to conduct atrial contraction. Imagine an old Casion keyboad on Mobitz setting that randomly doesn't keep the beat.
Tx. Poss heralds 3rd Degree HB.

• 2:1/3:1

x2/3 the no. of P Waves to QRS complexes. Note when the P wave may be hidden in the T wave - it can be identified as a regular distortion.
Tx. Poss heralds 3rd Degree HB.

Causes:
acute MI/IHD

Mobitz I & II = No Tx
2:1 = temp/perm pacing (*slow Vn rate)


Third Degree
Look at every PR interval in ECG (I know).
No conduction at all of atrial contractions.
No relationship between P wave, and ORS complex.
Abnormal QRS complexes. Ventricles depolarising from an ectopic foci in V muscle, via a slow 'escape mechanism'.

Causes:
conducting tissue disease (*fibrosis): transient - acute MI/chronic - fibrosis in Bundle of His/both bundles blocked

Tx = temp/perm pacing