3 Cardiac Arrhythmias
Learn how to assess patients with cardiac arrhythmias, interpret key ECG patterns, and select initial responses based on pulse and hemodynamic stability.
Assess the patient first
An ECG rhythm matters, but initial treatment is guided by the patient's condition. Assess responsiveness, pulse, airway, breathing, blood pressure, oxygenation, and signs of poor perfusion. includes hypotension, acutely altered mental status, shock, ischemic chest discomfort, or acute heart failure.
If there is no pulse, begin the cardiac-arrest pathway rather than an algorithm for a rhythm with a pulse. For a patient with a pulse, support airway and breathing, give oxygen if hypoxemic, apply cardiac monitoring, obtain vascular access, and obtain a -lead ECG when feasible. Do not delay urgent treatment to obtain an ECG.
Consider reversible causes, including ischemia or infarction, hypoxia, electrolyte or metabolic abnormalities, and medications or toxins.
Read the rhythm systematically
Use a rhythm strip or ECG to assess rate, regularity, P waves, PR interval, QRS width, and the relationship between atrial and ventricular activity. A rhythm strip helps identify rate and conduction patterns; a -lead ECG can add diagnostic information.
Rate: Decide whether the ventricular rate is slow, normal, or fast. The AHA algorithms use rates typically below beats per minute to prompt assessment for bradyarrhythmia and beats per minute or faster as a typical tachyarrhythmia rate. These are prompts for assessment, not stand-alone diagnoses.
Regularity: Determine whether the intervals are regular, regularly irregular, or irregularly irregular.
P waves: Check whether P waves are present and consistent, whether each is followed by a QRS complex, and whether each QRS is preceded by a P wave.
PR interval: Assess whether it is constant, prolonged, progressively lengthening, or unrelated to the QRS. A usual PR interval is seconds.
QRS width: A QRS duration of seconds or longer is wide. A wide-complex rhythm may arise in the ventricles or reflect abnormal conduction, so interpret it in clinical context.
Atrial–ventricular relationship: Look for dropped beats, more P waves than QRS complexes, or independent atrial and ventricular activity.
Recognize bradyarrhythmias
has a regular rhythm, a sinus P wave before each QRS, and a slow rate. It may be normal during sleep or in a well-trained athlete. Treat the cause and the patient's symptoms, not the number alone.
has a prolonged but constant PR interval, with every P wave conducted to a QRS. It is a conduction delay, not a dropped beat.
Second-degree AV block has intermittent failure of conduction from atria to ventricles. In , the PR interval progressively lengthens until a P wave is not followed by a QRS. In , intermittent P waves are not conducted, but the conducted beats do not show progressive PR lengthening. and higher-grade blocks may deteriorate and warrant prompt expert evaluation.
has no consistent relationship between P waves and QRS complexes: the atria and ventricles beat independently. A slow escape rhythm may be narrow or wide. If compromise is present, prepare for pacing and escalate care.
Manage bradycardia with a pulse
For a stable patient, monitor, obtain an ECG, and investigate and treat underlying causes. If bradycardia is causing compromise, support airway and breathing, provide oxygen as needed, monitor the patient, and establish vascular access.
The current AHA algorithm recommends atropine mg IV, repeated every minutes to a maximum total dose of mg. If atropine is ineffective, use transcutaneous pacing and/or an epinephrine or dopamine infusion; consider expert consultation and transvenous pacing.
When pacing, confirm that it produces mechanical capture and improves perfusion. Electrical capture on the monitor alone is not sufficient.
Distinguish common tachyarrhythmias
Sinus tachycardia is usually a regular narrow-complex rhythm with a sinus P wave before each QRS. It commonly reflects another problem, such as fever, pain, hypovolemia, hypoxia, or infection. Treat the underlying cause rather than reflexively suppressing the rate.
Regular narrow-complex SVT often begins and ends abruptly; P waves may be hidden in or close to the QRS. For a stable patient, vagal maneuvers are appropriate, and is used for a regular narrow-complex tachycardia. The AHA adult algorithm dose is mg as a rapid IV push followed by a saline flush; if needed, give mg. can cause brief flushing or a sense of chest discomfort. Use it only in the appropriate rhythm and setting; it is not a treatment for an irregularly irregular or polymorphic wide-complex rhythm.
Atrial fibrillation is irregularly irregular, with no consistent discrete P waves. Atrial flutter often has repetitive flutter waves; its ventricular rhythm may be regular or irregular depending on AV conduction. If AF or flutter with a rapid ventricular response causes hemodynamic instability, immediate is recommended. For stable patients, clinicians select rate- or rhythm-control treatment based on the clinical context.
If pre-excited AF is suspected, often presenting as a very fast, irregular, wide-complex rhythm, avoid AV-nodal blocking drugs and seek expert emergency care. Cardioversion is recommended when appropriate.
Ventricular tachycardia is generally a wide-complex tachycardia. Monomorphic VT has a consistent QRS shape, whereas polymorphic VT varies in QRS appearance. If the cause of a wide-complex tachycardia is uncertain, treat it as potentially ventricular and obtain expert help. In stable, regular monomorphic wide-complex tachycardia, the AHA algorithm allows consideration of . Do not give for unstable, irregularly irregular, or polymorphic wide-complex tachycardia. Avoid verapamil and diltiazem in wide-complex tachycardia.
Choose emergency electrical treatment
For a persistent tachyarrhythmia with a pulse that is causing , perform . Sedate when feasible, but do not delay lifesaving treatment. Confirm that the device is in sync mode before each shock.
If synchronization is not possible in a patient with a life-threatening rhythm, follow the appropriate defibrillation protocol and local resuscitation guidance. Pulseless VT and ventricular fibrillation are cardiac-arrest rhythms: begin CPR and use unsynchronized defibrillation, not .
Connect rhythm findings to action
First establish whether the patient has a pulse and whether is present. Read the rhythm by checking rate, regularity, P waves, PR interval, QRS width, and atrial–ventricular relationship; also consider reversible causes.
For compromised bradycardia, follow the atropine-to-pacing or infusion pathway. For an unstable tachyarrhythmia with a pulse, use . A pulseless patient requires the cardiac-arrest algorithm.