Cardiac Dysrhythmias and ECG Interpretation
5
Interpretation Steps
Rate rhythm P-waves PR QRS
3
Lethal Rhythms
VF pulseless VT asystole
2
Types of 2nd Degree
Type I Wenckebach vs Type II
Systematic 5-Step ECG Read
never skip a step, even when the rhythm looks obviousRate
Count R-R intervals. Regular? Use 300 method. Irregular? Count in 6 seconds x 10
Rhythm
Regular or irregular? Regularly irregular or irregularly irregular?
P Waves
Present? Uniform? One before each QRS? Ratio of P to QRS?
PR Interval
Normal 0.12-0.20 sec. Prolonged? Shortened? Progressive lengthening?
QRS Complex
Normal <0.12 sec. Wide = ventricular origin or bundle branch block
Critical Rhythms
Atrial Rhythms
AFib Irregularly irregular, no P waves, fibrillatory baseline
AFlutter Sawtooth pattern, regular atrial rate ~300, ventricular rate depends on block ratio
SVT Narrow complex, regular, rate 150-250, P waves often hidden, responds to adenosine
Ventricular Rhythms
VT Wide complex, regular, rate >100, may have pulse (cardiovert) or no pulse (defib)
VF Chaotic, no organized activity, NO pulse, immediate defibrillation
Torsades Polymorphic VT, twisting QRS axis, associated with prolonged QT, treat with magnesium
Heart Blocks
1st Degree PR >0.20 sec, all P waves conduct, benign, monitor only
2nd Type I Progressive PR lengthening then dropped QRS, usually benign (Wenckebach)
2nd Type II Constant PR then sudden dropped QRS, DANGEROUS, needs pacing
3rd Degree Complete dissociation of P waves and QRS, no relationship, pacing required
2nd degree Type II is MORE dangerous than Type I and requires pacing because it can progress to complete heart block without warning.
rhythm strips on the exam are tricky, practice makes perfect
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2nd degree Type II is MORE dangerous than Type I
Wenckebach (Type I) has a progressive PR prolongation before the dropped beat, which gives the heart a "warning." Type II drops beats without warning and can progress to complete heart block suddenly. Type II needs pacing.
Atropine may not work in infranodal blocks
Atropine speeds up the SA and AV nodes. If the block is below the AV node (infranodal), atropine cannot reach the problem. Type II and 3rd degree blocks with wide QRS are infranodal and need pacing, not atropine.
Synchronized cardioversion is for organized rhythms WITH a pulse
Sync mode times the shock to the R wave to avoid the vulnerable T wave period. Use it for unstable SVT, afib, aflutter, or VT with a pulse. Defibrillation (unsynchronized) is for VF and pulseless VT only.
Adenosine works for SVT only
Adenosine briefly blocks AV node conduction, which interrupts the reentry circuit in SVT. It will NOT convert atrial fibrillation, atrial flutter, or ventricular tachycardia. It may help diagnose aflutter by unmasking flutter waves.
Adenosine Specificity
Adenosine works on SVT. It does NOT work on atrial fibrillation or ventricular tachycardia. Wrong drug = wasted time.
Sync vs Unsync
Synchronized = organized rhythm with pulse. Unsynchronized (defib) = VF or pulseless VT. The machine needs an R wave to sync to.
The SA node is the power station that generates the electrical impulse. It fires at 60-100 beats per minute. If it fails, backup generators (AV node at 40-60, ventricles at 20-40) take over, but at slower rates.
The electrical signal passes through relay stations (AV node, Bundle of His, bundle branches). Heart blocks happen when one of these relay stations fails or delays the signal.
Type I (Wenckebach) is like a relay that gets progressively more tired until it skips one beat, then resets. Type II is like a relay that works fine then suddenly fails without warning. Type II is unpredictable and therefore scarier.
VF is like a house with all the wiring sparking randomly. VT is like one rogue wire sending rapid signals that override everything. Both prevent the pump from working properly.
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