Heart Blocks

A delay or block between the atria (P) and the ventricles (QRS)

Cardiac & EKG

1st-degree AV block

Usually benign

PR >0.20 s and constant; every P is followed by a QRS. Rate and rhythm usually normal.
Causes: beta blockers, CCBs, digoxin, amiodarone, high vagal tone, inferior MI, hyperkalemia, aging.
Care: usually no treatment; review meds; watch for progression.

2nd-degree type I (Wenckebach)

Mobitz I

PR gets progressively longer until one P is not followed by a QRS (dropped beat), then the cycle repeats. Ventricular rhythm irregular; QRS usually narrow.
Care: usually transient; treat only if symptomatic (atropine); review meds.

2nd-degree type II

Mobitz II: dangerous

PR constant, then a QRS is suddenly dropped without warning. QRS often wide (block below the AV node).
Danger: can progress suddenly to 3rd-degree block.
Care: transcutaneous pacing pads on, prepare for a pacemaker; atropine is unlikely to work.

3rd-degree (complete) block

Emergency

P waves and QRS complexes are completely independent: Ps "march through" at their own regular rate; PR varies with no pattern; atrial rate > ventricular rate (escape rhythm 20–60).
Care: transcutaneous pacing, dopamine or epinephrine infusion as a bridge, then a permanent pacemaker.

Compare at a glance

Block	PR interval	Dropped QRS?
1st degree	Long, constant	No
2nd, type I	Gets longer each beat	Yes, after the longest PR
2nd, type II	Constant	Yes, without warning
3rd degree	No relationship	P and QRS independent

Memory hook "If the R is far from P, then you have a first degree.
Longer, longer, longer, drop: then you have a Wenckebach.
If some Ps don't get through, then you have a Mobitz II.
If Ps and Qs don't agree, then you have a third degree."

Pacemaker nursing

Know the set rate; a pacer spike should be followed by a P (atrial) or a wide QRS (ventricular): capture.
Failure to capture: spike with no QRS after it. Failure to sense: spikes in the wrong place, including on T waves.
Transcutaneous pacing is painful: give analgesia/sedation as ordered; confirm a pulse matches the paced rate.

After a permanent pacer: limit raising the arm on the insertion side above the shoulder as instructed (often for a few weeks); watch the site for bleeding, hematoma, infection.
Carry the device ID card; tell providers before MRI (many devices are MRI-conditional only); keep phones and magnets ~6 in (15 cm) from the device.