Comprehensive Study Notes: Cardiac Arrhythmias (Chapter 25, Nursing Care of Patients With Cardiac Arrhythmias)

Cardiac Conduction System

• SA node rate: 60 \text{ to } 100\ \text{beats per minute}
• Atrioventricular (AV) node rate: 40 \text{ to } 60\ \text{beats per minute}
• Bundle of His
• Right and left bundle branches
• Purkinje fibers

Cardiac Cycle

• One heartbeat
• Electrical representation of contraction and relaxation of atria/ventricles

Components of a Cardiac Cycle

• P wave: first wave; represents atrial depolarization
• PR interval: from beginning of P wave to beginning of QRS complex; normal range 0.12 \text{ to } 0.20\ \text{seconds}
• QRS complex: Q, R, S waves; follows P wave
  • Q wave: first negative (downward) deflection
  • R wave: first positive (upward) deflection
  • S wave: second negative deflection after R (if Q wave exists)
  • Not all waves are present every time
  • Represents ventricular depolarization
• QT interval: beginning of Q wave to end of T wave; normal range 0.34 \text{ to } 0.43\ \text{seconds}
• ST segment: end of QRS complex to beginning of T wave

Electrocardiogram (ECG)

• Shows cardiac electrical activity
• 12-lead electrocardiogram (ECG) = 12 different cardiac views
• Waveforms change appearance in different leads
• Waveforms upright in lead II
• Continuous monitoring often in lead II

ECG Graph Paper

• Calibrated grids for measurement
• Time calibrated horizontally (across)
• Heavy lined blocks of 25 (5 × 5)
• Small square = 0.04\ \text{seconds} wide
• Five small squares = 0.20\ \text{seconds} wide
• Amplitude (height) measured vertically

ECG Graph Paper (continued)

• Example strips labeled: 3 seconds / 6 second strip
• Each small square width: 0.04\text{ s}; 5 small squares = 0.20\text{ s}

Isoelectric Line

• Baseline
• Seen with no electrical activity
• Straight line produced
• Waves deflect upward or downward from isoelectric line

Components of a Cardiac Cycle (continued_1)

• P wave
  • First wave
  • Represents atrial depolarization
• PR interval
  • Beginning of P wave to beginning of QRS complex
  • 0.12 \text{ to } 0.20\ \text{seconds}

PR Interval

• PR interval: duration from start of P wave to start of QRS complex

Components of a Cardiac Cycle (continued_2)

• QRS complex: Q, R, S waves
  • Q wave first negative (downward) deflection
  • R wave first positive (upward) deflection
  • S wave second negative deflection if Q wave, or first negative deflection after R
  • Not every wave is present every time
  • Represents ventricular depolarization

QRS Complex Discussion

• QRS complex with a Q wave
• QRS complex without a Q wave
• QRS complex without a Q or an S wave

QRS Interval

• Beginning of QRS complex to end of QRS complex
• Less than or equal to 0.10\ \text{seconds}

QRS Interval (visual)

• Diagrammatic label: QRS

Components of a Cardiac Cycle (continued_4)

• T wave: ventricular repolarization
• Follows QRS complex

T Wave

• Positive deflection
• T wave inverted/negative deflection may indicate ischemia

QT Interval (revisit)

• Beginning of Q wave to end of T wave
• Normal ranges: 0.34 \text{ to } 0.43\ \text{seconds}
• Varies based on gender, heart rate, age
• Prolonged or shortened QT interval can lead to ventricular arrhythmias

ST Segment

• End of QRS complex to beginning of T wave
• Depressed with nontransmural ischemia
• Elevated with transmural ischemia

ST Segment Inversion/ Depression and Elevation

• ST segment inverted or depressed indicates ischemia risk
• ST segment elevated indicates acute transmural ischemia

Interpretation of Cardiac Rhythms

• Six-step process:
  • Regularity of rhythm
  • Heart rate
  • P wave
  • PR interval
  • QRS interval
  • QT interval

Regularity: Normal Waveforms Are Equal Distances Apart

• R to R waves should be equal distance apart
• P to P waves should be equal distance apart

Heart Rate: Calculate the Rate for a Regular Rhythm

• For a regular rhythm:
  • HR = \frac{60}{\Delta t{RR}} where \Delta t{RR} is the interval between successive R waves in seconds

Heart Rate: Calculate the Rate for an Irregular Rhythm

• For irregular rhythms, estimate rate by counting the number of R waves in a 6-second strip and multiplying by 10
• Example practical approach: count R waves across a 6-second strip and compute HR \approx (\text{R-waves in 6s}) \times 10

EKG Setup and Electrode Placement

• Position the client in a supine position with chest exposed
• Wash the client's skin to remove oils
• Attach one electrode to each extremity (above wrists and ankles) and six chest electrodes
• Avoid chest hair; shave or clip if needed
• Typical lead placement:
  • RA, LA, LL, RL (limb leads)
  • Chest leads: V2, V6, V4, V3, V5 (commonly V1-V6 in standard precordial set)

Lead Locations (Example Layout)

• RA = right arm, LA = left arm, LL = left leg, RL = right leg (ground)
• Chest leads: V1, V2, V3, V4, V5, V6 positioned across the chest

Normal Sinus Rhythm

• What to look for: regular rhythm, normal rate, P waves before every QRS, PR interval 0.12–0.20 s, QRS interval < 0.10 s

Normal Sinus Rhythm Rules

• Rhythm: Regular
• Heart rate: 60 \leq HR \leq 100\ \text{beats per minute}
• P wave: Rounded, upright, before each QRS interval
• PR interval: 0.12 \text{ to } 0.20\ \text{seconds}
• QRS interval: < 0.10\ \text{seconds}

Arrhythmias: General Concepts

• Rhythm disturbances
• Impulse formation disturbed (automaticity issues)
• Disturbance in conduction (blocks, delays)

SA Node Arrhythmias

• Sinus bradycardia
• Sinus tachycardia

Sinus Bradycardia

• Rhythm: Regular
• Heart rate: < 60\ \text{beats per minute}
• P waves: Rounded, upright, before each QRS
• PR interval: 0.12 \text{ to } 0.20\ \text{seconds}
• QRS interval: < 0.10\ \text{seconds}
• Signs/symptoms: None or fatigue, fainting
• Treatment:
  • None if asymptomatic
  • Oxygen, atropine, dopamine or epinephrine, pacing

Sinus Tachycardia

• Rhythm: Regular
• Heart rate: 101 \le HR \le 180\ \text{beats per minute}
• P waves: Rounded, upright, before each QRS
• PR interval: 0.12 \text{ to } 0.20\ \text{seconds}
• QRS interval: < 0.10\ \text{seconds}
• Signs/symptoms: None; may have angina or dyspnea; older adults may be more sensitive
• Therapeutic interventions:
  • Treat underlying cause
  • Medications: Adenosine, beta blockers, calcium channel blockers

Atrial Arrhythmias

• Premature atrial contractions (PACs)
• Atrial flutter
• Atrial fibrillation

Premature Atrial Contractions (PAC)

• Rhythm: PACs interrupt rhythm
• Heart rate: Per underlying rhythm
• P waves: Early beat, abnormal shape
• PR interval: Usually normal
• QRS interval: < 0.10 s
• Signs/symptoms: None
• Therapeutic interventions:
  • None
  • Treat cause
  • Beta blocker

Atrial Flutter

• Flutter waves visible
• Conduction commonly 4:1 (example shown)

Atrial Fibrillation

• Rhythm: Irregularly irregular
• Heart rate: Atrial rate not measurable; ventricular rate:
  • < 100 = controlled response
  • > 100 = rapid ventricular response
• P waves: No identifiable P waves
• PR interval: None measurable
• QRS interval: < 0.10 s
• Signs/symptoms: Palpitations; faint radial pulse
• Therapeutic interventions:
  • Synchronized cardioversion if unstable
  • Medications: Beta blocker; calcium channel blocker
  • Anticoagulation
  • Ablation (after anticoagulation)
  • Surgical maze procedure

Ventricular Arrhythmias

• Premature ventricular contractions (PVCs)
• Ventricular tachycardia (VT)
• Ventricular fibrillation (V-fib)

Premature Ventricular Contractions (PVCs)

• Unifocal PVCs arise from one focus and look the same
• Multifocal PVCs arise from different foci and may look different
• Rhythm: PVCs interrupt rhythm
• Heart rate: Per underlying rhythm
• P waves: Absent in PVCs
• PR interval: None for PVCs
• QRS interval: PVCs > 0.10 s
• Signs/symptoms: Palpitations; fatigue, dizziness; possible severe arrhythmias
• Therapeutic interventions:
  • None
  • Treat cause
  • Antiarrhythmics: Amiodarone IV; Beta blocker; Lidocaine

PVC Pattern Classifications

• Unifocal PVCs look the same (one irritable ventricular area)
• Multifocal PVCs do not look the same (multiple irritable areas)
• Repetitive cycles/patterns:
  • Bigeminy: PVC every other beat
  • Trigeminy: PVC every third beat
  • Quadrigeminy: PVC every fourth beat
  • Couplet: Two PVCs in succession
  • Run of PVCs: Three or more PVCs in a row

Ventricular Tachycardia (VT)

• Rhythm: Usually regular
• Heart rate: 150 \text{ to } 250\$ ventricular beats per minute
• P waves: Absent
• PR interval: None
• QRS interval: > 0.10\ s
• Signs/symptoms: Dyspnea, palpitations, lightheadedness, angina, cardiac arrest
• Therapeutic interventions:
  • If pulseless VT: CPR, defibrillation, epinephrine, amiodarone (Cordarone), lidocaine (Xylocaine)
  • If stable: Antiarrhythmics

Ventricular Fibrillation (V-fib)

• Rhythm: Chaotic, extremely irregular
• Heart rate: Not measurable
• P waves: None
• PR interval: None
• QRS interval: None
• Signs/symptoms: Unconscious; no heart sounds, pulses; respiratory arrest; cyanosis; dilated pupils
• Therapeutic interventions:
  • ACLS protocols: Immediate defibrillation, CPR, epinephrine, amiodarone or lidocaine, endotracheal intubation and oxygen

Asystole

• Rhythm: None
• Heart rate: None
• P waves: None
• PR interval: None
• QRS interval: None
• Signs/symptoms: Unconscious; no heart sounds or pulses; respiratory arrest; cyanosis; dilated pupils
• Therapeutic interventions:
  • CPR
  • ACLS protocols: Endotracheal intubation with oxygen; epinephrine; treat cause

Review of Rhythms

• Dysrhythmias overview covering: atrial fibrillation, premature atrial complexes, premature ventricular complexes, ventricular tachycardia, etc.

Cardiac Pacemakers

• Generate an electrical impulse
• Traditional types: External and temporary; Internal and permanent
• Leads placed in atria, ventricle, or both
• Spike (vertical line) on ECG begins paced beat
• Leadless pacemakers: Newest technology

Dual-Chamber Permanent Pacemaker

• Example of pacing both atrial and ventricular chambers

Pacemaker ECG Tracings

• Atrial-only pacemaker: spike before P wave
• Ventricular-only pacemaker: spike before QRS complex
• Dual-chamber pacemaker: spikes before both P wave and QRS complex

Cardiac Pacemaker Problems

• Failure to sense
• Failure to pace
• Failure to capture

Nursing Care for Pacemakers

• Monitor ECG
• Monitor apical pulse
• Monitor for symptoms (e.g., dizziness, palpitations, changes in pulse)

Patient Pacemaker Education

• Incision care
• Activity restrictions
• Signs of infection to report
• Pacemaker ID card; periodic pacemaker checks
• Microwaves are safe; security devices are generally safe but can trigger
• Revo MRI SureScan pacing system safety
• Electromagnetic device cautions:
  • Avoid MRI, welder, radio tower, touching a running car engine
• If symptomatic, move away from potential EM exposure

Defibrillation

• Electrical shock to reset lethal ventricular arrhythmias (pulseless VT or V-fib)
• Use saline pads or conductive jelly with pads
• Paddles placed firmly against chest:
  • Right chest: second intercostal space, right of sternum
  • Left chest: fifth intercostal space at anterior axillary line
• Must announce “CLEAR” for safety

Placement of Defibrillator Paddles

• Diagrammatic reference to paddle placement (visual aid)

Synchronized Cardioversion

• Allows R wave to be sensed for safe delivery
• Used in arrhythmias if R wave present: VT with pulse; atrial fibrillation; atrial flutter; SVT
• Painful: sedation used
• Low energy: 25 \text{ to } 50\ \text{joules}

Automatic External Defibrillator (AED)

• Automatically analyzes rhythms
• Automatically delivers or prompts operator to deliver electrical shock if shockable rhythm (V-fib or VT) detected

Implantable Cardioverter Defibrillator (ICD)

• Automatically defibrillates when lethal rhythm detected
• Cardioverts when VT detected

Implanted Cardioverter Defibrillator (continued)

• Visual/diagrams of implanted device

Nursing Diagnoses for Arrhythmias

• Decreased Cardiac Output
• Anxiety