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Flashcards in Cardiac Rhythm Analysis Deck (39)
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What are the standard limb leads?

Lead 1 --> RA Neg, LA Pos
Lead 2 --> RA Neg, LL Pos
Lead 3 --> LA Neg, LL Pos


What are bipolar and unipolar leads?

Three standard leads are bipolar, chest leads are unipolar


What does P wave represent?

Atrial depolarization. Normal is smooth, rounded, upright, no more than 2.5mm high


What does PR interval represent?

Time taken from atrial depolarization and delay in conduction at the AV node.

Normal is 0.12 - 0.20 seconds


What does QRS complex represent?

Ventricular depolarization. Normal is 0.06 - 0.10 secs


What do Q waves represent?

Ventricular septum depolarization.
Should be less than 1 box wide and less than 1/4 height of the following R wave, or it is pathological.


What does ST segment represent?

End of ventricular depolarization and beginning of ventricular repolarization. Starts at J point, depression or elevation is anything +- 1mm from the isoelectric line


What does ST elevation represent?

Myocardial injury, pericarditis (Global ST), ventricular aneurysm, electrolyte imbalances


What does ST depression represent?

Myocardial ischemia, NSTEMI, electrolyte imbalance


What does T wave represent?

Ventricular repolarization.
In first 1/2, cells are in absolute refractory.
Normal T wave is upright, rounded, less than 5 boxes in height and larger than P waves.


What does a peaked T wave represent?

Myocardial infarction or hyperkalemia


What does a negative / inverted T wave represent?

Myocardial ischemia, subarachnoid bleed


What does a flattened T wave represent?



What is the QT interval?

Duration of ventricular depolarization and repolarization, in NSR should not exceed 0.44 secs. Should be 1/2 of RR.


What does lengthened QT interval represent?

Longer refractory period, caused by electrolyte imbalances, hypothermia, meds (amiodarone, haloperidol, antibiotics, antidepressants)


Normal Sinus Rhythm: Criteria?

HR 60-100, regular, PR normal, QRS normal


Sinus Bradycardia: Criteria, physiology, significance?

HR < 60, regular, PR normal, QRS normal

Caused by PSNS dominance, electro-conduction is normal but just slower

CO might be low, hypotension, decrease LOC, shock, ischemic chest discomfort. If HR is low an escape rhythm may take over


Sinus Bradycardia: Etiology and treatment?

Myocardial infarction, meds (Ca channel blockers, beta blockers), increased ICP

Treatment if symptomatic: Atropine 0.5mg IV push (can repeat every 3-5 mins max 3mg). If ineffective consider dopamine, epinephrine, cardiac pacing


Sinus tachycardia: Criteria, physiology, significance?

HR 100-150, regular, PR normal, QRS normal

Faster electro-conduction, SNS dominance

Diastolic filling time decreases as HR increases, decreased perfusion to coronary arteries, potential loss CO


Sinus Tachycardia: Etiology and treatment?

Anxiety, pain, shock states, stimulants

Treat underlying cause


Sinus arrhythmia: Criteria, physiology, significance?

Irregular rhythm, PR normal, QRS normal

SA node influenced by variation in PSNS, causes increase in rate during inspiration and decrease in rate during expiration.

Normal variation due to changes in intrathoracic pressure


Sinoatrial block vs Sinus arrest: Criteria, physiology?

Sinus block: Missing PQRST(s), pause length is exact multiple of the underlying R-R (maps out)
SA node generates an impulse on time but is blocked from exiting, atrial cells do not depolarize.

Sinus arrest: Missing PQRST(s), pause length is not an exact multiple of underlying rhythm
SA node fails to initiate an impulse, loss of automaticity, when SA node fires again it can begin at any time


Sinus block + arrest: Etiology and treatment?

Ischemia of SA node, inferior wall MI, sick sinus syndrome, meds (beta blockers, calcium channel blockers)

Review meds, if symptomatic may use atropine / pacing


What is altered atrial automaticity?

Cells other than the nodal cells can abnormally initiate an impulse (ectopic impulse). If it occurs at a fast rate, it will take over the SA impulses


What is re-entry?

Abnormal path of conduction where impulses from the ventricle travel back up to the atria usually through a secondary pathway and cause early atrial depolarization. Can happen several times in a circular pattern


How does thrombus formation occur with atrial rhythms?

Loss of atrial kick or abnormal contraction causes blood stagnating in the atria. 48-72 hrs later a thrombus forms.

RA thrombus --> Goes into lungs, pulmonary embolus
LA thrombus --> Goes into brain, causes stroke, or elsewhere in body


Premature atrial complex: Criteria, physiology, etiology?

Early beat, upright P, different shape than P waves in underlying rhythm

Cells with enhanced automaticity fire a premature ectopic beat which produces abnormal P wave. Sometimes this can depolarize the ventricle but sometimes ventricles in absolute refractory (non-conducted PAC)

Caused by excess SNS / Sympathomimetics, atrial enlargement (CHF), valvular heart disease


Atrial tachycardia: Criteria, physiology, etiology?

HR 150-250, regular rhythm, normal QRS, (PR may be unable to measure)

Re-entry circuit or enhanced automaticity, ectopic site with fast rate becomes pacemaker

Caused by excess SNS / Sympathomimetics, atrial enlargement (CHF), valvular heart disease


Atrial tachycardia: Significance?

1) Increases workload of the heart, increases myocardial O2 demand

2) Decreases diastolic filling time, decrease CAD blood supply

Eventually lead to myocardial ischemia and infarction


Atrial tachycardia: Treatment?

If asymptomatic: Vagal manoeuvres (bearing down, carotid sinus massage), adenosine, beta / Ca blockers, amio

If symptomatic: Synchronized cardioversion