Chapter 23: Management of Patients W/Arrhythmias and Conduction Disorders

SA Node

primary pacemaker

60-100 bpm

located in the right atrium

Atrioventricular (AV) Node

slows the impulse to allow ventricular filling (“atrial kick” provides 1/3 of total ejected volume)

Bundle of His and Purkinje Fibers

impulse moves down the right/left bundle branches into the Purkinje fibers, triggering ventricular contraction

Systole

depolarization

electrical stimulation

mechanical contraction

systole/diastole

Diastole

repolarization

electrical relaxation

mechanical relaxation

systole/diastole

Autonomic Control of Heart

HR is regulated by ANS, comprising sympathetic (adrenergic) stimulation

Sympathetic (adrenergic) Stimulation

Positive chronotropy (increased heart rate)

Positive dromotropy (increased AV Node conduction)

Positive inotropy (increased force of myocardial contraction)

Vascular effect: constriction of peripheral blood vessels, increased bp

Parasympathetic Stimulation

Negative chronotropy: decreased heart rate

Negative dromotropy: decreased AV conduction

Contractility: decreased force of atrial myocardial contraction 

Decreased sympathetic stimulation dilates arteries, lower bp

Obtaining ECG and Electrode Placement

Preparation: Washing the application area with soap and water, and clipping excess hair, reduces skin impedance and enhances electrode conductivity.

Preventing Artifact: Poor electrode adhesion causes artifact—distorted, irrelevant waveforms that obscure accurate electrical capture

Normal Variations of ECG

Because of these different viewpoints, a normal rhythm tracing will inherently look different across different leads, such as lead I compared to lead II or lead III

Identifying Changes in ECG

A change in the waveform can indicate an actual alteration in how the electrical impulse originates or is conducted, or it may simply result from changing the lead being viewed

Comprehensive Assessment of ECG

To accurately assess the heart and identify exactly where, when, and what abnormalities are occurring, healthcare providers must evaluate the ECG from every lead, not just a single view

P Wave

atrial depolarization

PR Interval

time for sinus stimulation to AV node conduction (0.12-0.20 sec)

QRS Complex

ventricular depolarization

<0.12 sec

ST Segment

early ventricular depolarization (monitored for ischemia)

T Wave

ventricular repolarization

QT Interval

total time for ventricular depolarization and repolarization

Determining Heart Rate Method 1: Regular Rhythms

accurate for regular rhythms

count number os small boxes within an RR interval and divide number 1500 by that number

Ex. 1500/10= 150 bpm

Determining Heart Rate Method 2: Irregular Rhythms

6 second method

alternative for irregular rhythms (less accurate)

count number of RR intervals within a 6 sec strip and multiply number by 10

Ex. 7 RR intervals x 10= 70 bpm

you must count the RR intervals, not QRS complexes because it might lead to an inaccurate high calculated high heart rate

Determining Atrial rate

Methods can also be used to calculate the atrial rate by measuring the PP interval instead of the RR interval

Simple 6 Step Pathway

rate, rhythm, P waves, RR interval, PR interval, QRS complex, ST segment and QT/QTc

Simple 6 Step Pathway: Rate

Count QRS complexes in a 6 sec strip and multiply by 10, or use box methods

Decide: bradycardia (<60), normal (60-100), or tachycardia (>100)

Simple 6 Step Pathway: Rhythm

Regular vs irregular

Measure RR intervals across the strip

If RR distances are equal (or vary <1 small box) its regular

If they vary its irregular

Simple 6 Step Pathway: P Waves

Are P waves present and consistent in shape?

Are there more P waves than QRS, fewer, none?

Simple 6 Step Pathway: PR Interval

Measure form the start of P to start of QRS

Is it within 0.12-0.20 secs, shorter or prolonged?

Ask: is the pr integral constant or does it change beat to beat

Simple 6 Step Pathway: QRS Complex

Measure the width 

Is it narrow (<0.12 secs) or wide (>0.12 secs)

Narrow: supraventricular origin 

Wide: ventricular origin or conduction delay

Simple 6 Step Pathway: ST Segment and QT/QTc

ST: is it isoelectric, elevated, or depressed?

QT: roughly < half the RR interval

If clearly prolonged, think QTc prolongation and risk of torsades

Normal Sinus Rhythm (NSR) ECG Characteristics

Ventricular and atrial rate: 60-100 bpm

Ventricular and atrial rhythm: regular

QRS shape and duration: usually normal, may be regularly abnormal

P wave: normal, consistent shape, always before QRS

PR interval: consistent, 0.12 to 0.20 secs

P:QRS ratio: 1:1

Management Strategies for NSR

Normal electrical conduction from SA node

No medical management required

Represents health heart function

Sinus Bradycardia

occurs when SA node creates an impulse slower than normal rate

Sinus Bradycardia Causes

Metabolic needs (sleep, athletic training, and hypothyroidism)

Vagal stimulation (vomiting, suctioning, and severe pain)

Meds (calcium channel blockers (nifedipine, amiodarone) and beta blockers

Idiopathic sinus node dysfunction

Increased intracranial pressure

Coronary artery disease

Sinus Bradycardia ECG Characteristics

Ventricular and atrial rate: <60 bpm

Ventricular and atrial rhythm: regular

QRS shape and duration: usually normal, may be regularly abnormal

P wave: normal, consistent shape, before QRS

PR interval: consistent, 0.12 to 0.20 secs

P:QRS ratio: 1:1

Sinus Bradycardia Management Strategies

Identify Causes and Symptoms 

No clinical instability/causative factors

Resolve causative factors prevent vagal stimulation, withhold beta blockers

monitor

Clinical instability

Administer atropine 0.5 mg IV bolus (repeat every 3-5 mins, max 3 mg)

If unresponsive to atropine

Emergency transcutaneous pacing or dopamine, isoproterenol, or epinephrine

Sinus Tachycardia (ST)

sinus node creates an impulse faster than normal rate

Sinus Tachy Causes

Physiologic or psychological stress (acute blood loss, anemia, shock, hypervolemia, hypovolemia, heart failure, pain, hypermetabolic states, fever, exercise, and anxiety)

Meds that stimulate sympathetic response (catecholamines, aminophylline, atropine), stimulants (caffeine and nicotine), and illicit drugs (amphetamines, cocaine, ecstasy)

Inappropriate Sinus Tachy

Enhanced automaticity of the SA node

Innate ability of cardiac cells to initiate an electrical impulse

Postural Orthostatic tachycardia Syndrome (POTS)

Tachycardia w/o hypotension and by presyncopal symptoms like palpitations, lightheadedness, weakness, and blurred vision with sudden postural changes

Sinus Tachy ECG Characteristics

Ventricular and atrial rate: >100 bpm (often <120 bpm)

Ventricular and atrial rhythm: regular

QRS shape and duration: usually normal, may be regularly abnormal

P wave: normal, consistent shape, before QRS (may be buried in T wave)

PR interval: consistent, 0.12 to 0.20 secs

P:QRS ratio: 1:1

Sinus Tachy Management Strategies

identify and abolish cause

Vagal Maneuvers: Valsalva, carotid massage, coughing, cold stimulus

Adenosine: Interrupts tachycardia

Hemodynamic instability: Synchronized cardioversion

stable/persistent: Beta blockers, calcium channel blockers, catheter ablation

Premature Atrial Complex (PAC)

electrical pulse starts in the atrium before the next normal impulse of the sinus node

usually seen w/tachycardia

Causes of PAC

Caffeine, alcohol, nicotine, stretched atrial myocardium (hypervolemia), anxiety, hypokalemia, hypermetabolic states, or atrial ischemia, injury, or infarction

PAC ECG Characteristics

Ventricular and atrial rate: depends on underlying rhythm 

Ventricular and atrial rhythm: irregular, early P waves, shorter PP interval, noncompensatory phase

QRS shape and duration: early QRS usually normal, may be abnormal or absent 

P wave: early, different shape, or hidden in T wave; others consistent 

PR interval: early PR shorer but normal (0.12-).2 secs)

P:QRS ratio: usually 1:1

PAC Management Strategies

Infrequent PACs (<6 mins); no treatment necessary. Monitor 

Frequent PACs (>6 mins): medical management → treat underlying cause (Reduce caffeine intake, Correct hypokalemia)

Atrial Fibrillation (A-Fib)

can result from diverse pathophysiological etiologies

results from abnormal impulse formation that occurs when a structural or electrophysiologic abnormalities alter atrial tissue causing a rapid, uncoordinated twitching of atrial musculature

AFib Risk factors

Alcohol use disorder, diabetes, exercise, family history, female sex, heart failure, hyperthyroidism, hypotension, MI, obstructive sleep apnea, smoking, obesity

Paroxysmal A-Fib

Sudden onset w/termination that occurs randomly or after an intervention; lasts <7 days but may recur

Persistent Afib

Continuous, lasting >7 d

Long Standing Persistent Afib

Continuous, lasting >12 mo

Permanent Afib

Persistent but decision has been made not restore or maintain sinus rhythm

Nonvalvular

Absence of moderate to severe stenosis or mechanical heart valve

Afib ECG characteristics

Ventricular and atrial rate: 300-600 bpm; usually 120-200 bpm in untreated afib

Ventricular and atrial rhythm: highly irregular

QRS shape and duration: usually normal, may be regularly abnormal

P wave:no discernible P waves; irregular undulating waves that vary in amplitude and shape are seen and referred to as fibrillatory or f waves

PR interval: can not be measured

P:QRS ratio: many:1

Afib Management Strategies: Stroke Prevention

Antithrombotic drugs: warfarin, DOACs, Factor Xa inhibitors, prescribed via CHA2DS2-VASc risk assessment 

Alternative: left atrial appendage occlusion (LAAO) (WATCHMAN for nonvalvular AF)

Afib Management Strategies: rate Control

Resting ventricular rate <80 bpm

Meds: beta blockers or non-dihydropyridine channel blockers

Afib Management Strategies: Rhythm Conversion

Pharmacologic cardioversion: Flecainide, doferilide, amiodarone

Electrical cardioversion: used to restore sinus rhythm

Requirement: if arrhythmia >48 hrs, anticoagulation or TEE

Afib Management Strategies: Surgical/Advanced Therapies

Options: catheter ablation, maze or mini-maze procedures, convergent procedure

Indication: for rhythms unresponsive to meds or electrical cardioversion

Atrial Flutter

Occurs due to a conduction deficit in the atrium and causes a rapid, regular atrial impulse at a rate between 250 and 400 bpm

Saw tooth on ekg

Atrial Flutter ECG Characteristics

Ventricular and atrial rate: 250 and 400 bpm; ventricular rate usually ranges between 75 and 150 bpm

Ventricular and atrial rhythm: atrial rhythm regular, ventricular rhythm regular but may be irregular due to change in AV conduction 

QRS shape and duration: usually normal, may be regularly abnormal

P wave: saw-toothed shape; referred to as F waves

PR interval: difficult to determine due to F waves

P:QRS ratio: 2:1, 3:1, 4:1

Management Strategies for Atrial Flutter

Vagal maneuvers or trial admin of adenosine (IV rapid admin followed by 20 mL saline flush and elevation of arm) to terminate tachycardia or visualize flutter waves 

Treated w/antithrombotic therapy, rate control, and rhythm control similarly to afib 

Electrical cardioversion is often successful in converting to sinus rhythm

Afib differences from A flutter

Chaotic irregular rhythm, no P waves, irregular RR intervals 

Causes: Hypertension, heart failure, valve disease

Symptoms: Palpations, fatigue, SOB

Treatment: Rate control, rhythm control, anticoagulation

A flutter differences from A fib

Rapid regular sawtooth pattern, flutter waves 

Causes: Similar to afib, Pulmonary disease

Symptoms: Often similar to afib

Treatment: Cardioversion, ablation, rate control, anticoagulation

Junctional Rhythm

no p waves

Occurs when AV node becomes pacemaker of the heart 

inverted p wave

Junctional Rhythm ECG Characteristics

Ventricular and atrial rate: 40-60 bpm

Ventricular and atrial rhythm: regular

QRS shape and duration: usually normal, may be abnormal

P wave: absent before QRS (inverted esp. Lead II) or after QRS

PR interval: consistent, <0.12 sec (if P is before QRS)

P:QRS ratio: 1:1 or 0:1

Management Strategies for Junctional Rhythm

Monitor for signs of reduced cardiac output 

Treatment same as sinus bradycardia

Atropine or pacing may be considered

Emergency pacing may be needed

Atrioventricular Nodal Reentry Tachycardia (AVNRT)

Benign non-life threatening arrhythmia goal is to alleviate symptoms and improve quality of life

Aim of therapy is to break reentry of the impulse

AVNRT ECG Characteristics

Ventricular and atrial rate {150-250 (atrial)}, {120-200 (ventricular)}

Ventricular and atrial rhythm: regular

QRS shape and duration: usually normal (narrow)

P wave: difficult to discern

PR interval: <0.12 sec (if P before QRS)

P:QRS ratio: 1:1, 2:1

Management Strategies for AVNRT

Alleviate symptoms and improve quality of life

Initial treat: catheter ablation (choice treatment)

Acute management: vagal maneuvers (IV adenosine bolus)

Pharm therapies: IV non-dihydropyridine  (CCBs, IV beta blocker, IV digoxin)

Unstable/ refractory causes (Electrical cardioversion)

Premature Ventricular Complex (PVC)

Impulse that starts in the ventricle and is conducted through the ventricles before the next normal sinus pulse

Causes of PVC

Intake of coffee, nicotine, alcohol, cardiac ischemia or infarction, heart failure, tachycardia, digitalis toxicity, hypoxia, acidosis, or electrolyte imbalances (hypokalemia)

PVC ECG Characteristics

Ventricular and atrial rate: depends on underlying rhythm

Ventricular and atrial rhythm: irregular due to early QRS, creates one shorter RR interval

QRS shape and duration: >0.12 sec; bizarre and abnormal (unifocal or multifocal)

P wave:visibility varies (absent, hidden in QRS/T, or before QRS w/different shape)

PR interval: If P before QRS <0.12 sec

P:QRS ratio: 1:1, 0:1

Management Strategies for PVC

Initial treatment: aim to correct underlying cause

Frequent and persistent PVC: may treat w/amiodarone or beta blockers

Note: long term pharmacotherapy is not usually indicated

Ventricular Tachycardia

3 or more PVCs in a row

emergency because pts is nearly always unresponsive

Risk Factors for V-tach

pts w/larger MIs and lower ejection fractions

V-tach ECG Characteristics

Ventricular and atrial rate: Ventricular is 100-200, martial rate depends in underlying rhythm 

Ventricular and atrial rhythm: usually regular

QRS shape and duration: 0.12 secs or more, bizarre normal shape 

P wave: difficult to detect, so atrial rate/rhythm may be indeterminable 

PR interval: very irregular if P waves are seen 

P:QRS ratio: difficult to determine but usually more QRS complexes than P waves 

V-tach Management Strategies: Stable VT

antiarrhythmic meds (amiodarone) or synchronized cardioversion

12 lead ECG, procainamide, sotalol, lidocaine, antitachycardia pacing

V-tach Management Strategies: Unstable VT

treated as V fib w/immediate defibrillation and CPR

Identify and treat underlying causes

V-tach Management Strategies: Symptomatic monophasic VT

Cardioversion is treatment of choice 

V-tach Management Strategies: Long Term

ICD considered for pts w/an ejection fraction less than 35%

V-tach Management Strategies: Torsades de Pointes

Immediate treatment required

Identify causes

Correcting electrolyte imbalances (IV magnesium)

IV isoproterenol pacing if associated w/bradycardia

Ventricular Fibrillation (V-Fib)

Rapid, disorganized ventricular rhythm that causes ineffective quivering of the ventricles

No atrial activity seen

Causes of V-Fib

Acute coronary artery disease, acute MI, untreated Vtach, cardiomyopathy, valvular heart disease, Brugada syndrome, acid-base and electrolyte abnormalities

V-Fib Characteristics

Ventricular and atrial rate: greater than 300 bpm

Ventricular and atrial rhythm: extremely irregular, w/o specific pattern

QRS shape and duration: irregular, undulating waves w/changing amplitudes; no recognizable QRS complexes

Management Strategies for V Fib

Characterized by absence of an audible heartbeat, palpable pulse, and respirations

Immediate electrical defibrillation and CPR are essential for survival

Antiarrhythmic drugs such as amiodarone may be indicated if defib attempts are unsuccessful

Idioventricular Rhythm

impulse starts in conduction system below the AV node

Idioventricular Rhythm ECG characteristics

Ventricular rate: 20 and 40 bpm; if rate exceeds 40, rhythm known as accelerated idioventricular rhythm 

Ventricular and atrial rhythm: regular

QRS shape and duration: bizarre, abnormal shape; duration is 0.12 secs or more

Management Strategies of Idioventricular Rhythm

Commonly causes pt to lose consciousness and experience signs of reduced cardiac output

Interventions follows ACLS guidelines: identify underlying cause administer IV epinephrine, atropine, and vasopressor meds, and initiate emergency transcutaneous pacing as needed

Ventricular Asystole

Flatline, characterized by absent QRS complexes confirmed in 2 different leads 

Ventricular Asystole ECG Characteristics

Characterized by absent QRS complexes confirmed in 2 different leads 

Occasionally P waves may be apparent for short duration

Management Strategies for Ventricular Asystole

Fatal w/o immediate treatment

Treated similarly to PEA, focusing in high quality CPR w/minimal interruptions

Rapid assessment to identity reversible causes (Hs and Ts: hypovolemia, hypoxia, hydrogen ion, hypo/hyperkalemia, hypothermia, tension pneumothorax, tamponade, toxins, and thrombosis 

Initiation of CPR, intubation, and establishment of IV access are the next recommended actions

Asystole

Appearance: Flat line (slight undulations) 

Mechanical Activity: No pulse

P wave and QRS: absent

Management Strategies: CPR, epi/vasopressin

Reversible Causes: Treat underlying cause (if identified)

Pulseless Electrical Activity (PEA)

Appearance: Organized electrical activity (P, QRS present)

Mechanical Activity: No pulse

P wave and QRS: Present, but no pulse

Management Strategies: CPR, Epinephrine/vasopressin, treat H’s and T’s

Reversible Causes: Hs and Ts (hypovolemia, hypoxia, etc.)

1st degree Atrioventricular Block

Occurs when all the atrial impulses are conducted through the AV node into the ventricles at a rate slower than normal

1st degree Atrioventricular block ECG Characteristics

Ventricular and atrial rate: depends on the underlying rhythm

Ventricular and atrial rhythm: depends on underlying rhythm 

QRS shape and duration: usually normal but may be abnormal

P wave: in front of the QRS complex; shows snus rhythm, regular shape

PR interval: greater than 0.20 secs; PR interval measurement is constant

P:QRS ratio: 1:1

Management Strategies for 1st degree atrioventricular block

Rarely causes any hemodynamic effect

Management of AV blocks is based on the cause and stability of the patient directed toward increasing heart rate to maintain normal cardiac output 

If stable w/o symptoms, no treatment may be indicated, or it may involve decreasing/eliminating the cause (withholding meds)

2nd Degree AV Block Type I (Wenchebach)

benign conduction delay at the AV node

PR interval is prolonged

2nd Degree AV Block Type I (Wenchebach) ECG Characteristics

Ventricular and atrial rate: depends on underlying rhythm, but ventricular rate is lower than the atrial rate

Ventricular and atrial rhythm: PP interval is regular, RR interval gradually shortens until there is another long RR interval 

QRS shape and duration: usually normal, may be abnormal

P wave: in front of the QRS complex; shape depends on underlying rhythm

PR interval: becomes longer w/each succeeding complex until there is a P wave not followed by QRS

P:QRS ratio: 3:2. 4:3, 5;4, and so forth

Management Strategies for 2nd Degree AV Block Type I (Wenchebach)

Same general AV block management as 1st degree block based in symptoms and cause

2nd Degree AV Block Type I (Mobitz II)

serious arrhythmia where electrical impulses are intermittently blocked below the AV node (His-Purkinje system), causing unexpected dropped QRS complexes without prior PR interval lengthening

2nd Degree AV Block Type I (Mobitz II) ECG Characteristics

Ventricular and atrial rate: depends on underlying rhythm, but ventricular rate is lower than the atrial rate

Ventricular and atrial rhythm: PP interval is regular, RR interval is usually regular but may be irregular depending on P:QRS ratio

QRS shape and duration: usually abnormal, may be normal

P wave:  in front of the QRS complex; shape depends in underlying rhythm

PR interval: constant for those P waves just before QRS complexes

P:QRS ratio: 2:1, 3:1, 4:1, 5:1, and so on

Management Strategies for 2nd Degree AV Block Type I (Mobitz II)

Same general AV block management, but if the block is related to necessary meds or other conditions, permanent pacemaker implantation may be indicated

temporary pacemaker may be necessary for severe symptomatic bradycardia