Cardiac Rhythms

Cardiac Rhythms

Introduction to Cardiac Rhythms

  • The heart beats due to electrical activity in the cardiac muscle, involving two main processes:   - Depolarization: Electrical impulse that initiates contraction of the heart.   - Repolarization: The heart muscle relaxes following contraction.

  • An Electrocardiogram (ECG) records the electrical activity of the heart but does not visualize cardiac structures. It helps identify areas of the heart with inadequate blood flow (perfusion).

ECG Waveforms and Intervals

  • Key waveforms and intervals observed in an ECG:   - P wave: Represents atrial depolarization.   - PR interval: Indicates time taken for the cardiac impulse to travel from the AV node; duration is 0.12 – 0.20 seconds.   - QRS complex: Represents ventricular depolarization; duration is 0.08 – 0.12 seconds.   - ST segment: Follows QRS and precedes ventricular repolarization; duration is 0.08 – 0.12 seconds.   - T wave: Reflects ventricular repolarization.   - QT interval: Duration for ventricular repolarization to complete; normal range is 0.36 - 0.44 seconds.

Cardiac Cycle and Electrical Activity

  • Waveform functions:   - P wave: Indicates atrial squeeze (depolarization).   - QRS complex: Indicates ventricular squeeze (depolarization).   - T wave: Indicates ventricular relaxation (repolarization).

  • The ECG waveforms are labeled alphabetically, initiating with the P wave. Depolarization transmits electrical impulses causing heart contractions, while repolarization involves relaxation and preparation for the next impulse.

Timing and Measurement of ECG

  • Small Boxes in ECG:   - Each small box equals 0.04 seconds.   - Five small boxes make up one large box, equating to 0.20 seconds.

  • Large Boxes in ECG:   - Each large box is 0.20 seconds.

  • Six-Second Method to Estimate Heart Rate:   - Count the number of large boxes (30 total in a 6-second strip) and the number of QRS complexes, then multiply by 10 to estimate beats per minute (bpm).     - Example: If 6 QRS complexes are counted in 6 seconds:       - 6imes10=60extbpm6 imes 10 = 60 ext{ bpm}.

Rhythm Analysis

  • Normal Heart Rate: Ranges from 60-100 bpm.

  • Bradycardia: Heart rate less than 60 bpm.

  • Tachycardia: Heart rate above 100 bpm.

  • ECG rhythm can be regular or irregular.

Steps for ECG Analysis

  1. Calculate heart rate.

  2. Determine if the heart rhythm is regular.

  3. Assess for P waves.

  4. Measure PR interval.

  5. Measure the duration of the QRS complex.

  6. Assess ST segment.

  7. Observe for changes in T wave.

  8. Measure the length of QT interval.

ST Segment and T Wave Changes

  • ST Segment: Should demonstrate a 1 mm change in elevation or depression from baseline; changes may indicate alterations in cardiac perfusion or electrolyte imbalances.

  • T Wave Changes:   - Peaking may indicate hyperkalemia (high potassium levels).   - Inversion may signify cardiac perfusion alteration (e.g., ischemia).

  • QT Interval: Should not exceed 0.45 seconds; prolonged QT may lead to lethal dysrhythmias.

Normal Sinus Rhythm

  • Normal conduction pathway begins at the SA node and proceeds to the AV node, then through the bundle of His, left and right bundle branches, leading to the Purkinje fibers.

Sinus Bradycardia

  • Definition: Heart rate slower than 60 bpm due to delayed electrical impulses from the SA node.

  • Causes: Genetic factors, sleep apnea, increased intracranial pressure, eating disorders, increased exercise tolerance, hypothyroidism, vagus nerve stimulation from frequent coughing or bowel straining.

  • Associated Conditions: Lyme disease, typhoid fever, malaria, medications, normal aging, and prolonged hypoxia.

  • Medications Causing Bradycardia:   - Parasympathomimetics: Acetylcholine   - Beta Blockers: Metoprolol   - Digitalis Glycosides: Digoxin   - Calcium Channel Blockers: Diltiazem   - Antiarrhythmics: Amiodarone   - Chemotherapy Agents: Thalidomide   - Lithium.

Impact on Health

  • Clients can be asymptomatic or symptomatic:   - Symptomatic signs: Fatigue, increased shortness of breath, dizziness.

  • Risk for falls due to symptoms.

Lab Testing for Bradycardia

  • Electrolytes: Potassium (K), Magnesium (Mg), Calcium (Ca).

  • Thyroid Hormone Panel: Assess for hypothyroidism.

  • Troponin Test: Measures cardiac-specific proteins to diagnose heart attacks or assess heart damage.

  • Toxicology Tests: Blood and urine.

Nursing Process

  • Role of Nurse:   - Implement fall precautions for symptomatic clients.   - Identify causes of bradycardia.   - Instruct on lifestyle changes to reduce injury risk.

  • Assessment Cues:   - Monitor for decreased cardiac output, dizziness, chest pain, near-syncope, mental status changes, shortness of breath.

Treatment and Therapies

  • Asymptomatic Clients: Observed with no active interventions.

  • Symptomatic Clients:   - Administer IV Atropine 1 mg (repeat every 3-5 minutes, max 3 mg).   - Temporary Transcutaneous Pacemaker for continuous instability or symptom severity.

Sinus Tachycardia

  • Definition: Occurs when the SA node fires at a rate over 100 bpm due to excessive sympathetic stimulation or decreased parasympathetic activity. Prolonged tachycardia can lead to decreased cardiac output.

  • Causes: Fluid volume loss (dehydration, bleeding), fluid volume excess, pain, fever, MI, shock, hyperthyroidism, stress.

  • Medications Affecting Heart Rate: Atropine, catecholamines, theophylline, illicit drugs (cocaine, amphetamines), caffeine, nicotine.

Sinus Tachycardia: Clinical Presentation

  • Symptoms may include:   - Palpitations   - Dizziness   - Lightheadedness   - Elevated temperature   - Chest pain   - Difficulty breathing—risk of falls if symptomatic.

Nursing Process for Sinus Tachycardia

  • Assessment: Recognize cues indicating instability (increased respiratory rate, low blood pressure).

  • Treatment and Therapies:   - Identify and manage triggers (fever, pain)   - Administer medications as ordered (e.g., adenosine for Supraventricular Tachycardia).

Premature Ventricular Contractions (PVCs)

  • Definition: Early heartbeat originating in the ventricles, disrupting normal rhythm.   - Features:     - Early beat with a wide, bizarre QRS complex.     - No clear P wave preceding it; followed by a compensatory pause.

Clinical Presentation of PVCs

  • Patients may report feeling a “skipped beat” or a “thump” in the chest after a compensatory pause.

  • PVCs may be benign in healthy individuals or occur due to cardiac muscle damage, electrolyte imbalances, caffeine, or alcohol.

Analysis and Monitoring

  • ECG Characteristics: PVCs appear more irregular due to early QRS complexes; QRS duration exceeds 0.12 seconds.

  • Holter Monitor: Used for outpatient monitoring of PVC episodes.

Nursing Process for PVCs

  • Evaluate frequency and pattern of PVCs; ensure safety and minimize risk from contributing factors like smoking and caffeine.

Treatment for PVCs

  • Medications: Beta-blockers, antiarrhythmics (e.g., Flecainide, Amiodarone).

  • Catheter Ablation: Considered if conservative measures fail after 30 days.

Premature Atrial Contractions (PACs)

  • Definition: Benign occurrences leading to early heartbeats from atrial tissues, possibly related to cardiac conditions or certain medications.

  • Generally asymptomatic; PACs do not pose significant health risks.

Nursing Considerations for PACs

  • Identify and modify lifestyle factors; mostly reassurance is needed for patients.

First-Degree Heart Block

  • Definition: A delay in conduction through the atria to the AV node, evident by a prolonged PR interval > 0.20 seconds.

  • Causes: Age, cardiac disease history, electrolyte imbalance, or medications.

  • Symptoms: Generally asymptomatic or may present with fall risks.

Nursing Role for First-Degree Heart Block

  • Assess medications history, interpret ECG for PR interval abnormality, and take adequate interventions accordingly.

Atrial Fibrillation (A-Fib)

  • Definition: An arrhythmia where multiple electrical stimuli cause chaotic atrial activity, decreasing cardiac output and risk of blood clots.

  • Associated conditions include uncontrolled glucose levels, hypertension, hyperthyroidism, and lifestyle factors.

Clinical Presentation of A-Fib

  • Patients may experience irregular pulse, hypotension, palpitations, shortness of breath, lightheadedness, and other symptoms affecting daily activities.

Nursing Management for A-Fib

  • Safety precautions for clients on anti-coagulants; educate on bleeding risks and healthy lifestyle modifications.

Atrial Flutter

  • Definition: A rapid, regular atrial rhythm (240-400 bpm) with multiple flutter waves on the ECG. The ventricular rate typically remains normal.

  • Risk factors and symptoms similar to A-Fib, with divergence specific to the regularity and rate of atrial contractions.

Supraventricular Tachycardia (SVT)

  • Definition: A rapid heart rhythm arising from above the ventricles, with heart rates typically of 100-220 bpm.

  • Clinical manifestations can occur abruptly; management focuses on stabilizing the patient and restoring normal rhythm.

Nursing Process for SVT

  • Thorough assessment, monitoring vital signs, and readying for potential intervention methods such as vagal maneuvers or IV adenosine administration for rhythm control.

This guide encompasses the intricate details of cardiac rhythms, their diagnostic approaches, clinical significance, and nursing roles in managing various conditions within cardiac studies. It provides comprehensive insights useful for understanding and interpreting cardiac rhythms effectively in clinical practice.