Rapid review II: slow rhythms, blocks, and the paced heart

1 · Sinus bradycardia

• Rate below 60 per minute. Regular. One upright P before every QRS. PR 0.12 to 0.20 second, constant. QRS less than 0.12 second.
• Priority: the rate is only a problem if perfusion is. Assess level of consciousness, blood pressure, chest pain, and shortness of breath before treating. A trained athlete at 48 per minute who feels well needs documentation, not atropine.

2 · Junctional rhythm

• Rate 40 to 60 per minute, accelerated at 60 to 100. Regular. P waves inverted, absent, or following the QRS. PR shorter than 0.12 second when a P precedes. QRS less than 0.12 second.
• Priority: the backup pacemaker took over, so ask why. Review digoxin, rate-slowing drugs, and potassium. Assess perfusion.

3 · First-degree atrioventricular block

• Rate usually normal. Regular. One P per QRS. PR longer than 0.20 second and constant. QRS less than 0.12 second.
• Priority: long but conducted. Monitor, document, and review the medications that lengthen conduction.

4 · Mobitz type I (Wenckebach)

• Atrial rate regular, ventricular response irregular in groups. More P waves than QRS complexes. PR lengthens beat to beat until one P is not conducted. QRS less than 0.12 second.
• Priority: usually benign and often transient after inferior infarction. Monitor, hold rate-slowing doses per order, and treat only if symptomatic.

5 · Mobitz type II

• Atrial rate regular, ventricular rate slower. More P waves than QRS complexes. PR constant on every conducted beat with no lengthening before the drop. QRS often 0.12 second or wider.
• Priority: unstable and prone to progressing. Place pacing pads on the patient, keep the defibrillator at the bedside, notify, and anticipate transcutaneous pacing.

6 · Complete (third-degree) heart block

• Atrial rate regular at 60 to 100; ventricular escape regular at 40 to 60 if junctional or 20 to 40 if ventricular. No relationship between them. P waves march through and behind QRS complexes. PR not measurable. QRS narrow or wide depending on the escape site.
• Priority: prepare for transcutaneous pacing, keep the pads on the patient, and do not leave the room. Anticipate a permanent device.

7 · Paced rhythms

• A vertical spike sits immediately before the chamber it paced: before the P wave in atrial pacing, before a wide QRS in ventricular pacing.
• Priority: a spike must be answered by a complex, and a complex must be answered by a pulse. Verify at the wrist.

8 · Pacemaker malfunction

• Failure to capture: spikes appear at the programmed interval with no complex after them, and the effective rate falls below the programmed rate.
• Failure to sense: spikes appear at intervals unrelated to the patient's own complexes, including one landing on a T wave, which can trigger ventricular tachycardia.
• Priority: assess perfusion, document a strip, and report both immediately.

Device care block

• Restrict movement of the arm on the operative side for the period ordered, and no lifting above shoulder level until cleared.
• Check the site each shift for hematoma, swelling, drainage, and redness.
• Report hiccups or chest wall twitching, which suggest lead displacement.
• No magnetic resonance imaging unless the device is labeled as conditional. Carry the device identification card.
• Keep a cell phone on the opposite side and at least six inches from the generator.
• For an implanted defibrillator: one shock with full recovery is reported to the cardiologist; repeated shocks, or any shock with ongoing symptoms, means emergency services. A person touching the patient during a discharge may feel a tingle and is not harmed.

Medication gate: count the apical pulse for one full minute before digoxin. Hold the dose for a rate below 60 per minute and report it. Treat nausea, anorexia, and yellow-green or halo vision as toxicity until proven otherwise, and remember that low potassium makes toxicity more likely at any level.

Memory hookSPIKE ALONE MEANS NO CAPTURE. SPIKE INTRUDING MEANS NO SENSE. Registered as B8-SPIKE-PAIR.

Digoxin and potassium values live at → BOOK 07 · P4. Drug class behavior lives at → BOOK 05 · P3.

Takeawaya slow rhythm is treated when the patient is symptomatic, and a paced rhythm is verified at the wrist, not on the screen.