Term
| What Are the Causes of Cardiac Arrhythmias? |
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Definition
Disturbances in automaticity
• Speeding up
• Slowing down
• Leads to abnormal beats from abnormal depolarizations • Abnormal rhythms
Disturbances in conduction
• Too fast: WPW, LGL
• Too slow: AV blocks
Combinations |
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Term
| How Do We Analyze for Abnormalities? on ekg |
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Definition
• The key is analysis of the waveform and the interrelationship of the P wave, QRS complex, and the PR interval
• Another key to determining the arrhythmia is the:
- Rate: difficult to determine at times on a monitor
- Rhythm
- Site of the dominant pacemaker |
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Term
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Definition
• Increased rate of discharge from the SA node
• Indicates, usually, a physiologic demand for increased cardiac output
- Exercise, fever, anxiety, hypovolemia
• Normal appearing narrow QRS complexes
• Regular rhythm
• Rate >100 bpm
• Normal P waves in a 1:1 ratio with the QRS complexes
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Term
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Definition
• Decreased rate of atrial depolarization due to slowing of the sinus node
• Several possible causes:
- Sinus node disease (sick sinus syndrome)
- Increased parasympathetic tone
- Drugs: digoxin, beta blockers, calcium channel blockers
• Normal appearing narrow QRS complexes
• Regular rhythm
• Rate < 60 bpm
• Normal P waves in a 1:1 ratio with the QRS complexes
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Term
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Definition
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• Common among children and young adults
• Heart rate varies with respiration
-Rate slows down during expiration and heart rate speeds up during inspiration
- Mediated by vagal tone
- Total variation is <10%
• In elderly, sinus arrhythmia may occur but it is not related to respiration
- Possible precursor to sick sinus syndrome |
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Term
| Wolff-Parkinson-White Syndrome |
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Definition
• Causes a pre-excitation syndrome
• Normally, electrical stimulus from the SA node
passes through the AV node to the ventricles • PR interval of 0.12–0.20 seconds
• In WPW, there is an accessory pathway (bundle of Kent) between the atrium and the ventricle which will cause pre-excitation of the ipsilateral ventricle
-short PR <.12 sec
-wide QWRS >.10 sec
-delta wave on R wave
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Term
| How Do We Identify Arrhythmias? |
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Definition
• Treat the patient, not the monitor
• Ask three questions:
- Is the QRS normal in appearance?
- Is there a P wave?
- What is the relationship between the P waves and the QRS complexes?
• In this order, this will identify the most life- threatening situations first. |
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Term
| step 1 of identifying arrhythmias |
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Definition
• Is the QRS complex normal in appearance?
• If no, think V Fib, V Tach, or asystole |
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Term
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Definition
• “Single most important rhythm to identify”
• Multiple areas in the ventricles display marked variation in depolarization and repolarization
• There is no organized ventricular depolarization; the ventricles do not contract as a unitàso...
• There is no cardiac output
• Most common mechanism of cardiac arrest resulting from myocardial ischemia or MI
• Coarse V Fib implies a recent onset; fine V Fib implies a considerable delay since onset
• There are no normal-appearing QRSs
• Rate is very rapid and usually too disorganized to count
• Rhythm is rapid and chaotic without pattern or regularity
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Term
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Definition
• Three or more beats of ventricular origin in succession with a rate >100 bpm
• No normal-looking QRS complexes—QRS complexes are wide
• Rhythm is regular
• May either be well tolerated or associated with hemodynamic compromise
- Compromise will depend on:
• Presence or absence of myocardial dysfunction • Rate of V Tach
• Signs/sxs: chest pain, SOB, low BP, shock, pulmonary congestion, decreased level of consciousness, CHF, acute MI |
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Term
| variations of ventricular tachycardia |
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Definition
• V Tach may be:
- Monomorphic, where all QRS complexes have the same shape
- Polymorphic, where the complexes have varying shapes
• No normal-appearing QRS complexes, usually bizarre
with notching, >0.12 seconds in duration • Rate >100 bpm and usually <220 bpm |
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Term
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Definition
• “Twisting of the points”
• Form of V Tach where the QRS complexes
appear to be constantly changing
• Gradual alteration in the amplitude and direction of the QRS complex
• Causes: drug toxicity—TCA, phenothiazines, organophosphate insecticides
- Idiosyncratic reaction to type I antiarrhythmics— quinidine, procainamide, disopyramide
- Hypokalemia, hypomagnesemia
- Eating disorder—bulemia, anorexia
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-undulating pattern |
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Term
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Definition
• Also called ventricular standstill
• Total absence of ventricular electrical activity
- P wave may occur, may have an agonal escape beat, but NO pulse
• With no ventricular depolarization there is no ventricular
contraction
• V Fib may masquerade as asystole so always check in two leads to verify asystole
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Term
| premature ventricular contractions |
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Definition
• Regular QRS complexes with occasional unusual-looking complexes interspersed
• Caused by depolarization that arises in either ventricle before the next expected sinus beatàprematurity
• Since PVCs arise in the ventricle the normal sequence of depolarization is changed—instead of the two ventricles depolarizing together, they depolarize sequentially—conduction occurs more slowly resulting in wide, bizarre QRS complexes
– ST segment and T wave usually in the opposite direction of the QRS complex
[image]
• Uniform/unifocal PVCs: have a constant morphology and are from the same focus
• Multifocal PVCs have variable morphology and arise from different foci
• PVCs may occur as isolated complex or occur repetitively
- >3 PVCs in a rowàV Tach
- If V Tach lasts >30 seconds àsustained V Tach
• QRS is wide and bizarre
• Irregular occurrence |
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Term
| Pulseless Electrical Activity (PEA) |
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Definition
-Normal-looking QRS complexes without a pulse
- The presence of some type of electrical activity other than
V Fib or V Tach but a pulse cannot be detected
- The causes of PEA are widely thought of as the 4Hs and 4Ts
• Hypovolemia • Hypoxia
• Hyper/hypokalemia and metabolic disorders • Hyper/hypothermia
• Toxicity
• Tension pneumothorax
• Tamponade (cardiac)
• Thromboembolism—MI or PE |
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Term
| step 2 of evaluating for cardiac arrhythmias |
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Definition
• Is there a P wave?
• When there are unorganized, very rapid electrical signals between the QRS complexes and NO discernable P wave, the rhythm is atrial fibrillation |
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Term
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Definition
• May result from multiple areas of reentry within the atria or multiple ectopic foci
- Sick sinus syndrome, hypoxia, pericarditis, increased atrial pressure (2° to CHF)
- Usually occurs with heart disease • Exception—“holiday heart” (alcohol)
• Atrial activity is very rapid—~400–700 bpm
- Each electrical impulse results in the depolarization of a small portion
(islet) of the atrial myocardium rather than the whole atrium à - No contraction of the atria as a whole
- No P waves but“fibrillatory waves”—nervous baseline
• Fibrillatory waves are irregular in rhythm and vary in size and shape
• Transmission of multiple atrial impulses into the AV node occurs at random, leading to an irregular rhythm
[image]
• Ventricular rate of A Fib is slower (averages 160– 180 bpm) than seen in atrial tachycardia or atrial flutter
• Atrial rate as a rule cannot be counted
• There is an erratic, wavy baseline
• Irregularly, irregular
• Ventricular depolarization (QRS complex) is usually normal |
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Term
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Definition
• There are P waves present, but they occur rapidly with a “sawtooth” or “picket fence” appearance
• Results from a reentry circuit within the atria
• Atrial rate is most commonly ~300 bpm with a 2:1 block present, making a ventricular rate of 150 bpm
• A flutter seldom occurs in the absence of organic disease
• Atrial rate 220–350 bpm
• Atrial rhythm is regular
• P waves look like “sawtooth” or “picket fence”
- Best seen in II, III, aVf
• Usually a normal QRS pattern
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Term
| step 3 for evaluating cardiac arrhythmias |
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Definition
• What is the relationship between the P waves and the QRS complexes?
• In a normal ECG, every QRS is preceded by a P wave, every P wave has a QRS associated with it, and the PR interval does not exceed 0.20 seconds
• Heart blocks are rhythms that are caused by altered conduction through the AV node
• Three degrees of block
- 1°: PR >0.20 sec, 1:1 ratio of P waves to QRS
- 2°: some P waves are blocked at the AV node
- 3°: complete dissociation between the P waves and QRS |
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Term
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Definition
• Defined as a delay or interruption in conduction between the atria and ventricles
• May be defined by the degree of the block or the site of the block unnecessary/only when symptoms occur |
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Term
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Definition
• A delayed passage of the impulse from the atria to the ventricles—not a true block but a prolonged PR interval
• Usually benign and treatment is usually unnecessary/only when symptoms occur
• Only abnormality is a PR interval of >0.20 seconds
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Term
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Definition
• Some impulses are conducted through the AV node and some impulses are blocked
• Two types:
- Type I, also called Mobitz I or Wenckebach
- Type II, also called Mobitz II |
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Term
| Mobitz I second degree AV block |
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Definition
• Often due to an increased parasympathetic tone or drug effect (digoxin, propranolol, verapamil)
• Usually transient
• Characterized by progressive prolongation of the PR interval—each atrial stimulus has a more difficult time passing through the AV node
• Decreased conduction velocity through the AV node occurs until an impulse is completely blocked
• Normal-looking QRS complexes
• Atrial rate is unaffected but ventricular rate < atrial rate
• Atrial rhythm is regular but ventricular rhythm is irregular
• Normal P waves
• PR interval will vary
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Term
| Mobitz II second degree AV block |
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Definition
• Usually associated with an organic lesion in the conduction pathway (usually below the AV node) and rarely the result of increased parasympathetic tone or drug effect
• PR interval does not lengthen before a dropped beat
• More than one nonconducted beat may occur in succession
• Complete heart block may develop from this • Often associated with a wide QRS complex
– QRS complex may be normal if the block occurs at the level of the bundle of His • Atrial rate is unaffected
• Ventricular rate < atrial rate
• Atrial rhythm is unaffected, but the ventricular rhythm is irregular
– More P waves than QRS complexes
• PR interval may be normal or prolonged, but it will remain constant
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Term
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Definition
• Indicates a complete absence of conduction between the atria and the ventricles
- Atria and ventricles are paced independently of each other
• Atrial rate is always equal to or greater than the
ventricular rate
• P wave will be normal in appearance
• QRS complex may have a normal or abnormal configuration
- Generally normal in appearance if the impulse is initiated above the bundle branch level
- If the block occurs at or below the bundle branch level, the QRS will appear wide due to the abnormal conduction through the ventricles
• QRS rate is usually < atrial rate:
- With an intranodal block, the ventricular rate is 40–60 bpm
- With an infranodal block, the ventricular rate is <40 bpm
- The ventricular rate is determined by the origin of the escape
rhythm
• Both the atrial and ventricular rates are regular • PR interval will vary
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