NCLEX Review Guide: Cardiac Dysrhythmias

Normal Conduction Pathway

• The cardiac conduction system begins with the sinoatrial (SA) node, the heart's natural pacemaker, which generates electrical impulses at a rate of 60-100 beats per minute. The impulse then travels through the atria to the atrioventricular (AV) node, which delays the impulse briefly before it continues through the Bundle of His, bundle branches, and Purkinje fibers to stimulate ventricular contraction.

Sinus Dysrhythmias

• Sinus tachycardia: Heart rate >100 bpm with normal P waves and regular rhythm, often caused by physiologic stress, fever, hypoxia, or medications. Assessment should focus on identifying the underlying cause while monitoring for signs of decreased cardiac output if rates exceed 150 bpm.
• Sinus bradycardia: Heart rate <60 bpm with normal P waves and regular rhythm, commonly seen in athletes, during sleep, or with increased vagal tone. It may also result from medications like beta-blockers or calcium channel blockers, hypothyroidism, or increased intracranial pressure.

Atrial Dysrhythmias

• Atrial fibrillation (A-fib): Characterized by chaotic atrial electrical activity resulting in irregular, often rapid ventricular response with absence of P waves, replaced by fibrillatory waves. Increases stroke risk due to blood stasis in atria, requiring anticoagulation therapy based on CHA₂DS₂-VASc score assessment.
• Atrial flutter: Presents with regular, rapid atrial activity (typically 250-350 bpm) creating characteristic "sawtooth" flutter waves (F waves), usually with 2:1 or 4:1 AV conduction. Management focuses on rate control, rhythm conversion, and anticoagulation similar to atrial fibrillation.

Ventricular Dysrhythmias

• Premature Ventricular Contractions (PVCs): Early, wide QRS complexes (>0.12 seconds) originating from ventricular tissue, often followed by a compensatory pause. Isolated PVCs in healthy individuals may be benign, but frequent PVCs (>30% of beats) or patterns like couplets, triplets, or R-on-T phenomenon require further evaluation.
• Ventricular tachycardia (VT): Three or more consecutive PVCs at a rate >100 bpm, presenting with wide QRS complexes, possible AV dissociation, and absence of preceding P waves. VT is a medical emergency that can rapidly deteriorate to ventricular fibrillation, especially in patients with structural heart disease.
• Ventricular fibrillation (VF): Characterized by chaotic, rapid ventricular depolarizations resulting in no effective contractions, appearing as irregular, erratic waveforms without discernible QRS complexes. VF is immediately life-threatening, requiring immediate defibrillation and CPR.

Heart Blocks

• First-degree AV block: Prolonged PR interval (>0.20 seconds) with all atrial impulses conducted to ventricles. Usually asymptomatic and requires no specific treatment, but warrants monitoring for progression to higher-degree blocks.
• Second-degree AV block, Mobitz I (Wenckebach): Progressive PR interval prolongation until a P wave fails to conduct, creating a pattern of grouped beats. Often caused by increased vagal tone or inferior wall MI affecting AV node.
• Second-degree AV block, Mobitz II: Constant PR interval with intermittent non-conducted P waves, resulting in a regular pattern of dropped QRS complexes. More concerning than Mobitz I as it often progresses to complete heart block and may require pacemaker placement.
• Third-degree AV block (Complete Heart Block): Complete dissociation between atrial and ventricular activity, with ventricles controlled by escape pacemaker (junctional or ventricular). Presents with regular P waves, regular QRS complexes, but no relationship between them.

ECG Interpretation Basics

• Systematic ECG interpretation should follow a consistent approach: rate, rhythm, P waves, PR interval, QRS duration, QT interval, ST segment, T waves, and overall impression. When analyzing dysrhythmias, focus particularly on the relationship between P waves and QRS complexes, regularity of the rhythm, and QRS morphology.

Clinical Manifestations

• Dysrhythmia symptoms vary widely based on the specific rhythm, rate, and underlying cardiac function. Common presentations include palpitations, lightheadedness, syncope, chest pain, dyspnea, fatigue, and in severe cases, signs of cardiogenic shock or sudden cardiac arrest. The nurse must correlate ECG findings with clinical presentation to determine urgency of intervention.

Pharmacological Management

• Antiarrhythmic medications are classified according to the Vaughan Williams classification (Class I-IV) based on their mechanism of action. Class I agents (sodium channel blockers) include procainamide and lidocaine; Class II (beta-blockers) include metoprolol and atenolol; Class III (potassium channel blockers) include amiodarone and sotalol; and Class IV (calcium channel blockers) include verapamil and diltiazem.

Electrical Interventions

• Synchronized cardioversion delivers a timed electrical shock synchronized with the R wave to terminate tachydysrhythmias while avoiding the vulnerable period of ventricular repolarization. It is indicated for unstable tachycardias with pulses, including atrial fibrillation, atrial flutter, and ventricular tachycardia with adequate perfusion.
• Defibrillation delivers an unsynchronized high-energy shock to completely depolarize the myocardium, terminating chaotic electrical activity in pulseless ventricular tachycardia or ventricular fibrillation. Unlike cardioversion, defibrillation does not synchronize with the cardiac cycle and uses higher energy levels (typically 120-200 joules biphasic).

Synchronized Cardioversion Procedure

1. Ensure equipment is ready (cardioverter, oxygen, suction, emergency medications)
2. Explain procedure to patient if conscious; administer sedation as ordered
3. Attach monitoring electrodes and ensure sync mode is activated (look for markers on R waves)
4. Select appropriate energy level (50-100J for atrial flutter/SVT, 120-200J for atrial fibrillation, 100J for VT)
5. Ensure all personnel are clear of patient and bed
6. Press and hold discharge buttons until shock is delivered (may be delayed due to synchronization)
7. Reassess rhythm and patient's hemodynamic status

Permanent Management Options

• Permanent pacemakers provide electrical stimulation to maintain adequate heart rate when the heart's intrinsic pacemaker function is compromised. Modern pacemakers are programmable with various modes (e.g., VVI, DDD) that determine which chambers are sensed and paced. Nursing care includes monitoring for complications like infection, lead displacement, and device malfunction.
• Implantable cardioverter-defibrillators (ICDs) combine pacemaker functions with the ability to detect and terminate life-threatening ventricular arrhythmias through antitachycardia pacing, cardioversion, or defibrillation. ICDs are indicated for patients at high risk for sudden cardiac death, including those with prior cardiac arrest, sustained VT, or severe left ventricular dysfunction.

Nursing Assessment

• Comprehensive assessment of patients with dysrhythmias includes cardiac monitoring, vital signs with orthostatic measurements, assessment of peripheral perfusion (capillary refill, skin temperature, color), level of consciousness, urine output, and presence of symptoms like chest pain, dyspnea, dizziness, or palpitations. The nurse should also evaluate for precipitating factors such as electrolyte imbalances, hypoxia, drug effects, or cardiac ischemia.

Nursing Interventions

• Priority nursing interventions for dysrhythmias include maintaining a patent airway, administering oxygen as needed, establishing IV access, continuous cardiac monitoring, frequent vital sign assessment, and preparation for emergency interventions. For specific dysrhythmias, interventions may include medication administration, preparing for cardioversion/defibrillation, or initiating temporary pacing as ordered.

Patient Education

• Patient education for dysrhythmia management includes medication teaching (purpose, dosage, administration, side effects), recognition of symptoms requiring medical attention, lifestyle modifications to reduce triggers, and specific instructions for device management if applicable. For patients with ICDs, provide psychological support and education regarding device activation, electromagnetic interference precautions, and driving restrictions.

Similar Dysrhythmias

Treatment Decisions

• Treatment decisions for dysrhythmias are based on hemodynamic stability, underlying cause, and specific rhythm identified. Stable dysrhythmias often allow time for pharmacological interventions, while unstable presentations require immediate electrical intervention. The ACLS algorithms provide standardized approaches based on rhythm and patient stability.

ECG Pattern Recognition

• Develop systematic pattern recognition by focusing on key characteristics: regularity (regular vs. irregular), rate (bradycardia, normal, tachycardia), P wave presence and morphology, PR interval, QRS width, and relationship between P waves and QRS complexes. Practice with multiple examples of each dysrhythmia to build recognition skills.

NCLEX Preparation Strategies

• For NCLEX questions related to dysrhythmias, focus on patient safety, prioritization of care, and recognition of life-threatening conditions. Practice questions that require you to identify rhythms from ECG strips, determine appropriate nursing interventions, and recognize complications of treatments or devices.

Self-Assessment Checklist

• Use this checklist to ensure comprehensive understanding of cardiac dysrhythmias before your NCLEX examination.