Heart block poem: the nursing mnemonic for EKG heart blocks

The heart block poem is a four-line mnemonic that nursing students have used for decades to memorize the EKG patterns for all four types of atrioventricular (AV) heart block. Each line maps directly to a specific rhythm: one delayed signal, one progressively failing signal, one intermittently absent signal, and one completely dissociated signal.

If you can recite the poem and match each line to its EKG criteria, causes, and treatment, you have a solid foundation for rhythm strip interpretation in clinical and NCLEX settings alike.

The heart block poem

If the R is far from the P, then you have a First Degree.

If PR gets longer and longer before the QRS drop, it must be a Wenckebach.

If PR stays normal and QRS quits, it must be a Type II Mobitz.

If Ps and Qs beat independently, it must be a Third Degree.

Quick-reference table

Atrioventricular blocks occur when conduction from the atria to the ventricles through the AV node is delayed, intermittently blocked, or completely blocked. The four types represent a clinical spectrum from benign to immediately life-threatening.

Printable heart block poem

A one-page printable version of the poem and rhythm strip comparison table is available as a free PDF: download the heart block poem PDF. The PDF is sized for a single sheet of paper and works well taped inside a clinical binder or study notebook. It pairs the four poem lines with their matching EKG criteria so you can scan it during telemetry rotation or while drilling for NCLEX.

First degree heart block

Poem line: If the R is far from the P, then you have a First Degree.

What it is

First degree AV block is a conduction delay — not a true block — at the level of the AV node. Every atrial impulse still reaches the ventricles, but it takes longer than normal. Because no beats are dropped, first degree block is hemodynamically well tolerated in most patients.

EKG criteria

• PR interval greater than 200 ms (0.20 sec) on every beat
• Every P wave followed by a QRS complex — no dropped beats
• Normal QRS morphology (unless a coexisting bundle branch block is present)
• Regular rhythm

The normal PR interval is 120–200 ms. In first degree block, the interval is prolonged but consistent from beat to beat.

Causes

• Inferior wall MI or ischemia (the right coronary artery supplies the AV node in most patients)
• Increased vagal tone (athletes, during sleep, vagal maneuvers)
• Beta-blockers, calcium channel blockers, digoxin, amiodarone
• Lyme disease (the most common cardiac manifestation of Lyme disease is AV conduction disturbance)
• Hyperkalemia or hypokalemia
• Age-related fibrosis of the conduction system

Symptoms and nursing management

Most patients with first degree AV block are asymptomatic. It is frequently discovered incidentally on a routine 12-lead EKG. No specific treatment is required for isolated first degree block.

Nursing priorities:

• Identify and treat any reversible cause (medications, electrolyte imbalance, ischemia)
• Monitor for progression to higher-degree block, particularly if the underlying cause is an acute MI
• A markedly prolonged PR interval (> 0.26 sec) with symptomatic bradycardia may warrant atropine

No pacing is required for uncomplicated first degree block.

Second degree heart block: Wenckebach (Mobitz type I)

Poem line: If PR gets longer and longer before the QRS drop, it must be a Wenckebach.

What it is

Wenckebach block — also called Mobitz type I — is an intermittent conduction failure at the AV node. The AV node conducts progressively less efficiently with each beat until one impulse fails entirely and the QRS is dropped. After the pause, the AV node recovers and the cycle repeats.

The result is a characteristic grouped beating pattern on the rhythm strip sometimes described as the “footprint of a limping man”: each cycle’s QRS complexes get slightly closer together until one disappears, then a longer pause, then the pattern repeats.

EKG criteria

• Regular atrial rhythm (consistent P-P interval)
• Irregular ventricular rhythm
• PR interval progressively lengthens with each beat in the cycle
• Dropped QRS complex after the longest PR interval
• Shorter PR interval on the beat immediately following the dropped complex — then the lengthening resumes
• Group beating is the visual hallmark

Causes

• Inferior MI (the most common structural cause — the RCA supplies the AV node)
• Increased vagal tone
• Drug toxicity (digoxin, beta-blockers, calcium channel blockers)
• Acute rheumatic fever
• Post-cardiac surgery

Symptoms and nursing management

Many patients are asymptomatic. Some report palpitations, weakness, or lightheadedness, particularly when the ventricular rate drops significantly.

Wenckebach is generally considered the more benign of the two second-degree subtypes:

• If the heart rate is above 40 bpm and the patient is asymptomatic, observation is appropriate
• For symptomatic bradycardia: atropine 0.5 mg IV (can repeat up to 3 mg total)
• Temporary transcutaneous pacing if atropine fails and the patient is hemodynamically unstable
• Most cases resolve when the precipitating cause is treated

Key nursing action: monitor the rhythm continuously and reassess hemodynamics. The rhythm can fluctuate, especially in the setting of acute inferior MI.

Second degree heart block: Mobitz type II

Poem line: If PR stays normal and QRS quits, it must be a Type II Mobitz.

What it is

Mobitz type II is an infranodal block — the conduction failure occurs below the AV node, in the bundle of His or the bundle branches. The AV node itself conducts normally, which is why the PR interval stays constant. But the infranodal system fails intermittently, dropping QRS complexes without any warning.

This is the dangerous second-degree block. Because the site of block is below the AV node, the backup pacemaker cells (if needed) are slow, unreliable ventricular escape cells firing at 20–40 bpm. There is a significant risk of abrupt progression to third degree (complete) heart block.

EKG criteria

• Regular atrial rhythm
• Constant PR interval on conducted beats — no lengthening before the dropped beat
• QRS complexes absent intermittently and without predictable pattern
• QRS is often wide (≥ 0.12 sec) because the block is at the level of the bundle branches
• May occur as 2:1, 3:1, or higher ratios (two or more P waves for every QRS)

The constant PR interval with sudden QRS disappearance is the defining feature that distinguishes Mobitz II from Wenckebach.

Causes

• Anterior MI (the left anterior descending artery supplies the bundle branches — anterior MI can disrupt infranodal conduction)
• Severe coronary artery disease
• Structural heart disease (cardiomyopathy, calcific valve disease)
• Acute myocarditis
• Digoxin toxicity

Symptoms and nursing management

Patients may be asymptomatic if the ventricular rate remains adequate, but Mobitz II carries high risk of sudden hemodynamic collapse. Even an asymptomatic patient requires urgent management planning.

Nursing priorities:

• Continuous cardiac monitoring — watch for deterioration to third degree block
• Establish IV access and have atropine, transcutaneous pacemaker, and code cart at bedside
• Atropine is less reliable for infranodal blocks — it may paradoxically worsen the block in some cases
• Most patients with Mobitz II require a permanent pacemaker, regardless of current symptoms
• Discontinue digoxin if it is a contributing cause
• Dopamine or epinephrine infusion may be needed for hemodynamic support if deterioration occurs

The clinical priority with Mobitz II is anticipation: treat this rhythm as a precursor to complete heart block until proven otherwise.

Third degree (complete) heart block

Poem line: If Ps and Qs beat independently, it must be a Third Degree.

What it is

Third degree AV block — complete heart block — is the most severe conduction disturbance in the AV block spectrum. No atrial impulses reach the ventricles at all. The atria and ventricles beat completely independently, each driven by its own pacemaker: the SA node drives the atria, and a junctional or ventricular escape rhythm drives the ventricles.

Cardiac output depends entirely on the escape rhythm. Junctional escape rhythms (40–60 bpm, narrow QRS) are more reliable; ventricular escape rhythms (20–40 bpm, wide QRS) are slower and far less stable.

EKG criteria

• Regular atrial rhythm (consistent P-P interval)
• Regular ventricular rhythm (consistent R-R interval), but at a slower independent rate
• No fixed relationship between P waves and QRS complexes — the PR interval varies randomly across the strip
• P waves “march through” the QRS complexes without affecting them
• Ventricular rate 20–40 bpm (ventricular escape) or 40–60 bpm (junctional escape)
• QRS may be narrow (junctional escape, block at AV node) or wide (ventricular escape, block below the bundle of His)

The defining feature is complete AV dissociation: P waves and QRS complexes have no relationship to each other.

Causes

• Inferior MI (complete block at the AV node — more likely to have junctional escape, better prognosis)
• Anterior MI (infranodal complete block — ventricular escape, worse prognosis)
• Lyme disease (can cause complete heart block, often reversible with antibiotics)
• Surgical complication (valve surgery, septal defect repair)
• Digoxin toxicity
• Age-related conduction system fibrosis (Lev’s disease, Lenègre disease)
• Congenital complete heart block

Symptoms and nursing management

Third degree heart block with ventricular escape is a cardiac emergency. Patients typically present with:

• Syncope or near-syncope (Stokes-Adams attacks)
• Severe symptomatic bradycardia
• Hypotension and hemodynamic instability
• Signs of heart failure (dyspnea, pulmonary edema)
• Angina from reduced cardiac output

Nursing priorities — act immediately:

1. Call for help and notify the physician or provider
2. Apply transcutaneous pacing pads and initiate transcutaneous pacing — this is the emergent bridge
3. Confirm mechanical capture – a palpable pulse with each pacing stimulus. Electrical capture alone (a QRS spike on the monitor) is not enough; if there is no pulse, increase the energy or reposition the pads
4. Establish IV access; dopamine or epinephrine infusion for hemodynamic support
5. Prepare for urgent transvenous pacemaker placement — the definitive bridge to permanent pacing
6. Permanent pacemaker is the standard of care for acquired complete heart block

Note on atropine: atropine is ineffective for complete heart block and should not be relied upon as primary treatment. It may temporarily increase the atrial rate but cannot restore AV conduction.

Comparing the four types: clinical decision table

The heart block song

Some nursing students find a sung or chanted version easier to retain than spoken lines. A widely circulated version set to a simple chant rhythm goes:

If the R is far from P – first degree, first degree.

Longer, longer, longer, drop – Wenckebach, Wenckebach.

Constant PR, QRS quits – Mobitz II, Mobitz II.

P and QRS don’t agree – third degree, third degree.

The repetition of the block name at the end of each line turns the poem into a call-and-response format, which works well when studying with a partner. There is no single “official” heart block song; different nursing programs and NCLEX review courses use slightly different wording. What matters is the underlying logic each version encodes: prolonged PR for first degree, progressive lengthening then drop for Wenckebach, constant PR with sudden drop for Mobitz II, and complete dissociation for third degree.

Clinical urgency ladder

One of the most useful things the poem does is force you to rank the four types. From lowest to highest urgency:

Medications that cause or worsen AV blocks: digoxin (all four types, particularly second and third degree in toxicity), beta-blockers (slow AV conduction, worsen all types), calcium channel blockers (diltiazem and verapamil especially), and amiodarone (can prolong PR and cause higher-degree block). In any patient with a new AV block, check their medication list before assuming a structural cause.

How to measure the PR interval on a rhythm strip

Knowing the poem helps you name the rhythm. Knowing how to measure the PR interval is how you confirm it.

1. Find a clear P wave with a QRS following it
2. Mark the start of the P wave – where the waveform first lifts off the isoelectric line
3. Mark the start of the QRS complex – where the first deflection (Q or R wave) begins
4. Count the small boxes between those two marks: each small box = 40 ms on a standard strip running at 25 mm/sec
5. Five small boxes = 200 ms = the upper limit of normal

If the interval is greater than five small boxes on every beat: first degree. If it lengthens across beats: Wenckebach. If it stays fixed while QRS complexes randomly disappear: Mobitz II. If P-to-QRS intervals vary with no pattern: third degree.

The key technique for spotting Wenckebach is to measure the PR on the first beat of each cycle, then the second, then the third. Each should be longer than the last. Then a QRS drops. Then the PR resets.

Distinguishing Mobitz I from Mobitz II: the most common NCLEX trap

Both Mobitz I and Mobitz II are second-degree blocks, both have dropped QRS complexes, and both can present with bradycardia. The question that trips students up: if you just see a dropped beat, how do you know which one it is?

The answer is the PR interval on the conducted beats:

• Wenckebach (Mobitz I): The PR interval on the conducted beats is not the same – it gets longer with each beat before the drop. Look at several consecutive PR intervals. If they are measurably different, it is Wenckebach.
• Mobitz II: The PR interval on every conducted beat is identical. If you measure three conducted beats and all three have the same PR, it is Mobitz II.

A 2:1 block – where every other QRS is dropped – is the hardest special case. When there is only one PR interval to measure before each drop, you cannot determine whether it is lengthening. In that situation, additional context (QRS width, the territory of any MI, whether the block improves with atropine) is needed to classify it. NCLEX will not usually require you to classify a 2:1 block from a strip alone; the question will give you enough context.

Common confusions

First degree vs. normal sinus rhythm: In normal sinus rhythm the PR interval is 120–200 ms. In first degree block it is greater than 200 ms. This is easy to overlook on a strip – measure, do not estimate.

Wenckebach vs. sinus pause: Both produce a pause in the rhythm. In Wenckebach, you can find the P wave before the dropped QRS if you look carefully – it is there, it just failed to conduct. In a sinus pause, the SA node itself did not fire, so there is no P wave at all during the pause.

Third degree vs. second degree with high block ratio: In high-ratio second degree block (3:1 or 4:1), most P waves do not conduct, and the ventricular rate is slow. The key difference from third degree: in second degree block the PR intervals on conducted beats are consistent (either lengthening as in Wenckebach or constant as in Mobitz II). In third degree block there are no consistent PR intervals – the relationship is entirely random.

NCLEX tips for heart blocks

NCLEX heart block questions test your ability to distinguish between the four types and identify the correct nursing priority. Here are the patterns most commonly tested:

• Wenckebach vs. Mobitz II is the most common discrimination question. The key distinction: Wenckebach has a progressively lengthening PR before the drop; Mobitz II has a constant PR. If the question says “PR lengthens,” it’s Wenckebach. If it says “PR constant” or “PR unchanged,” it’s Mobitz II.

• Mobitz II is always more dangerous than Wenckebach. If a question asks which patient to assess first or which rhythm requires more urgent intervention, choose Mobitz II. It can deteriorate to complete heart block without warning.

• Complete heart block + hemodynamic instability = transcutaneous pacing first. NCLEX expects you to know that atropine is unreliable for complete heart block. The correct first intervention when a patient with third degree block is unstable is transcutaneous pacing, not atropine.

• Inferior MI → Wenckebach or third degree (usually junctional escape, better prognosis). The right coronary artery supplies the AV node. Anterior MI → Mobitz II or infranodal complete block (ventricular escape, worse prognosis). The territory of infarction helps you predict the type of block.

• When you see a strip with P waves and QRS complexes at different rates with no relationship — that is third degree. Don’t let NCLEX distract you with a normal-looking PR interval in part of the strip. If atrial and ventricular rates are independent, it’s complete heart block.

Related resources

For a broader foundation in cardiac rhythm interpretation, the EKG interpretation cheat sheet covers normal intervals, common arrhythmias, and a systematic approach to reading rhythm strips. Electrolyte disturbances — particularly hyperkalemia and hypokalemia — are a common cause of AV conduction changes; see electrolyte imbalances for nursing students for a full clinical reference.