Rhythm Mechanisms

Question 1

Sinus Rhythm

Answer 1

Normal heart rhythm - normal electrical activity starting in the SA node, heads down the normal conduction pathway through the atria, antrioventricular (AV) node and bundle, right and left bundle branches, and pukinje fibers.

Fires at rate of 60-100bpm

Rhythm: R-R and P-P intervals are regular
Rate: 60-100bpm
P waves: positive, precedes each QRS complex, all look alike
PR interval: 0.12 to 0.20 sec and constant
QRS duration: 0.11 sec or less

Question 2

Sinus Bradycardia

Answer 2

SA node fires at a rate slower than expected for the patients age

Heart rate is 60bpm or less

Rhythm: R-R and P-P intervals are regular
Rate: Less than 60bpm
P waves: positive, precedes each QRS complex, all look alike
PR interval: 0.12 to 0.20 sec and constant
QRS duration: 0.11 sec or less

Causes: prolonged standing, stimulation of the vagus nerve, coughing, vomiting, straining to have a bowel movement, sudden exposure of the face to cold water.

Other causes: Disease of the SA node, hyperkalemia, hypokalemia, hypothermia, hypothyroidism, hypoxia, increased intracranial pressure, inferior myocardial infraction, medications (calcium blockers, digitalis, beta-blockers, amiodarone, and sotalol), sleep apnea, post heart transplant.

What to do about it: assessment (no symptoms, no treatment needed). If symptomatic, assess patients oxygen saturation level and determine if signs of increased breathing effort are present. Give supplemental oxygen, establish IV access and obtain 12 lead ECG. Atropine is drug of choice for SB

Question 3

Sinus tachycardia

Answer 3

SA node fires at a rate faster than normal for the patients age. Begins and ends gradually.

Rhythm: R-R and P-P intervals are regular
Rate: ventricular rate over 100bpm (max 220bpm)
P waves: positive, precedes each QRS complex, all look alike
PR interval: 0.12 to 0.20 sec and constant
QRS duration: 0.11 sec or less

Causes: acute myocardial infraction, anemia, anxiety, fear, caffeine, dehydration, drugs, exercise, fever, heart failure, hyperthyroidism, hypoglycemia, hypoxia, infection, medications, pain, panic attack, pericarditis, pneumothorax, postural changes, pregnancy, shock, sepsis

What to do about it: what is the underlying cause? (Fluid replacement, pain, removal of offending medication or substances, reducing fever). Lifestyle changes.

Question 4

Sinus arrhythmia

Answer 4

SA node fires irregularly. Sinus arrhythmia usually occurs at a rate of 60-100bpm (most common type of sinus arrhythmia)

Rhythm: irregular and often phasic with breathing (heart rate increases during inspiration, R-R intervals shorten. heart rate decreases with expiration, R-R intervals lengthen)
Rate: 60-100bpm
P waves: positive, precedes each QRS complex, all look alike
PR interval: 0.12 to 0.20 sec and constant
QRS duration: 0.11 sec or less

Causes: occurs with phases of breathing and changes in intrathoracic pressure. Heart rate increases with inspiration and decreases with expiration.

Non respiratory sinus arrhythmia may result from effects of medication or carotid sinus pressure

What to do about it: usually does not require treatment unless accompanied by a slow heart rate that causes hemodynamic compromise. IV atropine may be indicated to treat.

Question 5

Sinoatrial block

Answer 5

Sinoatrial block is called sinus exit block. SA node’s pacemaker cells initiate an impulse, but it is blocked as it exits the SA node, resulting in periodically absent PQRST complexes.

Rhythm: Irregular because of the pause - pause is exact distance of P-P intervals (even multiple) between it
Rate: normal but varies due to pause
P Wave: when present, positive and upright, precedes QRS complex and look alike
PR interval: when present 0.12-0.20sec and constant
QRS duration: 0.11sec or less

Causes: hypoxia, damage or disease to the SA node from CAD, myocarditis, or acute MI; carotid sinus sensitivity; increased fatal tone on the SA node and medication

What to do about it: depend on number of sinus beats blocked. No symptoms, patient is observed. SA block episodes are frequent, IV atropine, temporary pacing, or insertion of permanent pacemaker.

Question 6

Sinus arrest

Answer 6

Disorder of impulse formation. SA node’s pacemaker cells do not initiate an electrical impulse for one or more beats, resulting in absent PQRST complexes.

Rhythm: irregular; more than one missing PQRST and is not the same distance as other P-P intervals
Rate: normal
P Waves: when present, positive and upright, precedes QRS, look a like
PR intervals: when present, 0.12-0.20sec and constant
QRS duration: 0.11sec or less

Causes: damage to or disease of the SA node from CAD, acute MI or rheumatic disease, carotid sinus pressure, a sudden increase of parasympathetic activity on the SA node, stimulation of the pharynx, obstructive sleep apnea, medications

What to do about it: signs and symptoms are observed from carotid sinus sensitivity, vagal stimulation, removal of tight clothing are option. If hemodynamic compromise present, IV atropine, temporary pacing or both.

Question 7

Atrial dysrhythmias: mechanisms

Answer 7

Reflect abnormal electrical impulse formation and conduction in the atria.

Result from altered automaticity, triggered activity, or reentry.

Altered automaticity and triggered activity are disorders of impulse formation.

Reentry is a disorder in impulse conduction

Include:
(altered automaticity) premature atrial complexes (PAC), multifocal atrial tachycardia (MAT), and atrial fibrillation (AFib)
(Reentry) atrial flutter, AVNRT, and AVRT

Question 8

Premature beats

Answer 8

Premature beats are identified by the following site of origin:

-Premature atrial complexes (PACs)
-Premature junctional complexes (PJCs)
-Premature ventricular complexes (PVCs)

Question 9

Premature patterns

Answer 9

Couplet - two premature beats in a row
Runs or Bursts - three or more premature beats in a row
Bigeminy - every other beat is a premature beat
Trigeminy - Every third beat is a premature beat
Quadrigeminy - every fourth beat is a premature beat

Question 10

Premature atrial complex (PAC)

Answer 10

Early beat occurring before the next expected beat

Rhythm: irregular - early beat
Rate: usually within normal range
P waves: premature, positive (upright) that differ in shape from sinus P waves. Early P waves that may or may not be following QRS complex
PR interval: normal or prolonged depending on prematurity of beat
QRS duration: 0.11sec or less (may be wide or absent)

Causes: altered automaticity or reentry. Other - acute coronary syndromes, atrial enlargement, digitalis toxicity, electrolyte imbalance, emotional stress, heart failure, mental and physical fatigue, caffeine, drugs, medications

What to do about it: correcting underlying cause - correcting electrolyte imbalances, reducing stress, reducing or eliminating stimulants, treating heart failure

Question 11

Noncompensatory pause

Answer 11

Follows a PAC, representing the delay during which the SA node resets its rhythm for the next beat

Question 12

Compensatory pause

Answer 12

If the period between the complex before and after a premature beat is the same as two normal R-R intervals

Question 13

How to find out if it’s a noncompensatory or compensatory pause?

Answer 13

To find out whether the pause after a premature complex is compensatory or noncompensatory, measure the distance between R-R intervals of 3 normal beats. Then compare that measurement with the distance between the R-R intervals of 3 beats, one of which includes the premature complex.

Pause is noncompensatory if the period between complex before and after a premature beat is less than two normal R-R intervals

Pause is compensatory if the period between the complex before and after premature beat is the same as two normal R-R intervals

Question 14

Abberrantly conducted premature atrial complexes

Answer 14

If a PAC occurs very early, the right bundle branch can be slow to respond to the impulse. The impulse travels down the left bundle branch with no problem. Stimulation of the left bundle brace subsequent results in stimulation of the right bundle branch. The QRS will appear wide (greater than 0.11sec) because of the delay in ventricular depolarization.

PACs associated with a wide QRS complex are called aberrantly conducted PACs, indicating that conduction through the ventricles is abnormal

Question 15

Nonconducted (or blocked) premature atrial complexes

Answer 15

When a PAC occurs very early and close to the T wave of the preceding beat, only a P wave may be seen with no QRS after it, appearing as a pause. This type of PAC is called nonconducted or blocked PAC because the P wave occurred too early to be conducted

Question 16

Wandering Atrial Pacemaker (WAP) aka Multiform Atrial Rhythm (MAR)

Answer 16

Requires at least three different p waves seen in the same lead

P waves, size, shape, and direction vary, sometimes from beat to beat

Rhythm: irregular
Rate: 60-100bpm (if rate is faster than 100bpm, its termed Multifocal Atrial Tachycardia)
P waves: size, shape, direction may change form beat to beat, may be upright, inverted or biphasic, rounded, flat, pointed, notched, or buried in QRS
PR interval: varies as pacemaker site shifts from SA node to ectopic
QRS duration: 0.11sec or less

Causes: observed in normal hearts, during sleep, can occur with underlying heart disease

What to do about it: usually resolves on its own

Question 17

Multifocal atrial tachycardia

Answer 17

When wandering atrial rhythm is associated with ventricular rate of more than 100bpm

Rhythm: irregular
Rate: over 100bpm
P waves: size, shape, direction may change form beat to beat, may be upright, inverted or biphasic, rounded, flat, pointed, notched, or buried in QRS; at least 3 different P wave configurations
PR interval: varies as pacemaker site shifts from SA node to ectopic
QRS duration: 0.11sec or less

Causes: may involve altered automaticity or triggered activity. May be seen in older adults with severe COPD, coronary syndromes, heart failure, pneumonia, hypoxia, valvular heart disease, digoxin toxicity.

What to do about it: consult cardiologist to start treatments. Beta blocker, calcium blocker, pacemaker.

Question 18

Supraventricular Tachycardia

Answer 18

Begin above the bundle of his. Include rhythms that begin in the SA node, atrial tissue, or AV junction

3 examples of SVT

-Atrial tachycardia (AT)
-Atrioventricular nodal reentrant tachycardia (AVNRT)
-Atrioventricular reentrant tachycardia (AVRT)

Question 19

Atrial tachycardia

Answer 19

3rd most common type of SVT

Regular rhythm that arises from an ectopic focus in the atria at a rate faster than 100bpm and does not require the AV node’s participation to maintain the dysrhythmia

Rhythm: regular
Rate: 101-250bpm
P waves: 1 P wave precedes QRS complex; P wave differ in shape; isoelectric baseline is usually present between P waves; P waves will be negative if rhythm originates in low portion of atrium. Could be hard to distinguish P waves from T waves
PR interval: may be shorter or longer; difficult to measure because P waves could be hidden in the T waves
QRS duration: 0.11sec or less

Causes: acute illness with excessive catecholamine release, digitalis toxicity, electrolyte imbalance, heart disease, infection, pulmonary embolism, stimulant use

What to do about it: applying pulse oximeter, administering oxygen, obtaining vital signs, IV access, 12 lead ECG.

Question 20

Paroxysmal supraventricular tachycardia (PSVT)

Answer 20

Describes a rapid, regular SVT that starts and ends suddenly

PSVT may las for minutes, hours, or days

Question 21

Synchronized Cardioversion

Answer 21

Type of electrical therapy during which a shock is timed or programmed for delivery during ventricular depolarization

Delivering a shock during the QRS complex reduces the potential for the delivery of current during ventricular depolarization including the vulnerable period of the T wave

Question 22

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Answer 22

Most common SVT

Results from a reentry circuit that uses two separate pathways leading into the AV node. One pathway conducts impulses rapidly but has a long refractory period (slow recovery time). The other pathway conducts impulses slowly but has a short refractory period (fast recovery time).

Caused by single or multiple PACs.

Rhythm: regular
Rate: 150-250bpm
P waves: often hidden in QRS, can have a negative P wave after QRS; atria depolarized after the ventricles, the P wave typically distorts the end of the QRS complex
PR interval: not measurable
QRS duration: 0.11 sec or less

Causes: often seen young adults who have no structural heart disease or ischemic heart disease. Occurs in patients with COPD, CAD, valvular heart disease, heart failure and digitalis toxicity. Can be triggered by hypoxia, stress, anxiety, caffeine, sleep deprivation and medications.

What to do about it: pulse oximeter, administering supplemental oxygen, IV access, and sedation.

Question 23

Preexcitation

Answer 23

Refers to the premature activation of the ventricles by a supraventricular impulse arising from an accessory pathway

Question 24

Atrioventricular reentrant tachycardia (AVRT)

Answer 24

Most common type of SVT.

Number of atrial impulses reaching the ventricles may approach 300 - 350bpm, significantly increasing risk of ventricular fibrillation

Question 25

Wolff-Parkinson-White (WPW) Pattern

Answer 25

Most common form of preexcitation

Includes triad of findings that consists of the following:

1. A short PR interval
2. A wide QRS complex
3. A delta wave (initial slurred deflection at the beginning of the QRS complex that may be positive or negative)

Rhythm: regular
Rate: 60-100bpm
P waves: Normal and positive, unless WPW is associated with AFib
PR interval: 0.12sec or less if P waves are observed because impulse travels quickly across accessory pathway, bypassing normal delay in AV node
QRS duration: 0.12sec or more; slurred upstroke of the QRS complex (delta wave)

Causes: no associated heart disease
Symptoms associated with: anxiety, chest discomfort, dizziness, lightheadedness, palpitations, shortness of breath during exercise, signs of shock, weakness.

What to do about it: vegan maneuvers, medications such as adenosine, digoxin, diltiazem, and verapamil should be avoided

Question 26

Atrial flutter

Answer 26

Reentrant rhythm in which an irritable site within the atria fires regularly at a very rapid rate.

Reentry circuit around the right atrium’s tricuspid valve

Atrial waveforms are produced that resemble the teeth of a saw or a picket fence; called flutter waves or “F” waves

Rhythm: atrial reg; ventricular reg or irregular
Rate: atrial rate ranges from 240 to 300bpm; ventricular rate will not exceed 180bpm
P waves: No P waves observed
PR interval: is not measurable
QRS complex: is 0.11sec or less (if the flutter waves are buried in the QRS complex or if an intraventricular conduction delay exists, the QRS will appear wide)

Question 27

Atrial fibrillation (AFib)

Answer 27

Most common dysthymia

Occurs because of altered automaticity in one or several rapidly firing sites in the atria or reentry involving one or more circuits in the atria

Baseline looks erratic; these wavy deflections are called fibrillatory waves or f waves

Rhythm: ventricular rhythm irregular
Rate: atrial rate 300 to 600bpm; ventricular rate variable
P waves: no identifiable P waves, fibrillation waves present; erratic, baseline
PR interval: not measurable
QRS duration: 0.11sec or less

Question 28

Atrial fibrillation (AFib) associated with other dysthymias

Answer 28

Paroxysmal AFib - AFib that last 7 days or less with or without intervention

Persistent AFib - AFib that last more than 7 days

Long standing AFib - AFib that lasts 12 months or longer

Permanent AFib - long standing AFib that is refractory to cardioversion; this term is also used when both patients and his or her physician make a joint decision to stop further attempts to restore or maintain sinus rhythm

Nonvalvular AFib - AFib that occurs in the absence of rheumatic mitral stenosis, a mechanical or bioprosthetic heart valve, or mitral valve repair

Question 29

Premature Junctional Complexes (PJCs)

Answer 29

Rhythm: irregular
Rate: normal
P waves: may occur before, during or after the QRS; if visible, the P wave is inverted in leads II, III, and aVF
PR interval: If a P wave occurs before QRS, the PR interval will be usually 0.12sec or less; no P wave = no PR interval
QRS interval: 0.11sec or less

Has a noncompensatory (incomplete) pause.

Pause represents the delay during which the SA node resets the rhythm for the next beat.

PJCs can occur in patterns - couplets, bigeminy, trigeminy, quadrigeminy

Question 30

Junctional Escape Beat (JEB)

Answer 30

If the junctional complex comes late, it is called a junctional escape beat.

Rhythm: irregular (late beats)
Rate: normal range
P waves: may occur before, during, or after the QRS; if visible, the P wave is inverted in leads II, III, aVF
PR interval: If P wave occurs before the QRS, the PR interval is less than 0.12sec; if no P wave = no PRI
QRS duration: 0.11sec or less

Question 31

Junctional (escape) Rhythm

Answer 31

Several sequential junctional escape beats

Rhythm: regular
Rate: 40-60bpm
P waves: may occur before, during, or after QRS; if visible, the P wave will be inverted in leads II, III, aVF
PR interval: if P wave occurs before QRS, the PRI will be 0.12sec or less; no P wave = no PRI
QRS duration: 0.11sec or less

Question 32

Junctional bradycardia

Answer 32

AV junction paces the heart at a rate slower than 40bpm

Question 33

Accelerated junctional rhythm

Answer 33

AV junction speeds up and fires 61 to 100bpm. Caused by altered automaticity of the bundle of his

Rhythm: regular
Rate: 61 - 100bpm
P waves: may occurs before, during, or after the QRS: if visible, the P wave is inverted in lead II, III, aVF
PR interval: if a P wave occurs before the QRS, the PRI will usually be 0.12sec or less; if no P wave = no PRI
QRS duration: 0.11sec or less

Cause: associated with altered automaticity or triggered activity. Acute MI, cardiac surgery, chronic obstructive pulmonary disease, digitalis toxicity, hypokalemia, rheumatic fever.

What to do about it: monitor

Question 34

Junctional Tachycardia

Answer 34

Ectopic rhythm that begin the pacemaker cells found in the bundle of His

Exists when 3 or more sequential PJCs occur at a rate of more than 100bpm

Rhythm: ventricular rhythm regular, but could be irregular
Rate: 101 to 220bpm
P wave: p wave may be inverted in lead II, III, aVF
PR interval: if P wave occurs before the QRS, the PRI will be 0.12sec or less; if no P wave = no PRI
QRS duration: 0.11sec or less

Causes: disorder of impulse formation (automaticity). Acute coronary syndrome, digitalis toxicity, heart failure, or theophyline administration

What to do about it: consultation, vagal maneuvers, IV adenosine