KINS 4640 Rate and Rhythm

rate

cardiac cycles per minutes

normal SA node rate

60-100 bpm

sinus bradycardia

sinus rhythm <60 bpm

sinus tachycardia

sinus rhythm >100 bpm

overdrive suppression

the SA node fires fastest, so it suppresses all slower backup pacemakers

inherent backup (ectopic rates)

atrial 60-80; junctional (AV) 40-60; ventricular 20-40 bpm

rate method 1

count large boxes between R waves: 300, 150, 100, 75, 60, 50

rate if <60 bpm

count cycles in a 6 second strip and add a 0

rate method 2 (regular rhythm)

1500/number of small boxes between R waves (0.04 × 1500 = 60 s)

rate method 3 (irregular rhythm)

1500/mm from first to last R, x number of cycles in between ( 1500/98 × 5 = 76.5 bpm)

rhythm checklist

do P and R rates match? one P per QRS? do the waves look alike? check PR and QRS widths

normal PR interval

0.12-0.20 s (start of P to start of QRS) long = AV block

QRS width check

Q to end of S in limb leads >0.12 s = bundle branch AV block

5 arrhythmia cases

irregular rhythms, escape, premature beats, tachyarrhythmias, heart blocks

wandering pacemaker

irregular, normal rate (<100), 3+ different P wave shapes, variable PR

multifocal atrial tachycardia (MAT)

like wandering pacemaker but fast (>100); 3+ P shapes; common in COPD

atrial fibrillation (AFib)

no real P waves, wavy chaotic baseline, irregularly irregular RR; atria quiver at 350+

what irregular rhythms share

P shape varies, atrial rate irregular, ventricular rhythm irregular

escape rhythm

a backup focus takes over and paces at its own inherent rate

escape beat

a backup focus briefly escapes and fires just one beat

PAC (premature atrial contraction)

early beat with an odd-looking P wave; normal narrow QRS; timing resets

PVC (premature ventricular contraction)

early, wide, tall/deep QRS with no P; ventricles not full; compensatory pause after

unifocal vs multifocal PVCs

unifocal = all the same shape; multifocal = different shapes

R on T phenomenon

PVC lands on T wave; can trigger VT/VF (dangerous)

bigeminy/trigeminy/quadrigeminy

PVC every 2nd/3rd/4th beat

frequent PVCs

>5/min

run of PVCs

3 or more in a row = ventricular tachycardia; NSVT lasts <30 s

atrial flutter

identical sawtooth P waves, 250-350 bpm; several P waves per QRS

AFib vs flutter

flutter = identical regular sawtooth; AFib = variable chaotic, no clear P waves (350-450)

ventricular tachycardia (VT)

3+ PVCs in a row, 150-250 bpm, wide QRS, no P waves; very bad

ventricular fibrillation (VF)

chaotic, no P or QRS, 350-450; no cardiac output; emergency, defibrillate now

asystole

flatline, no electrical activity; the very worst

heart block

conduction delayed or stopped (SA node, AV node or below); seen as prolonged time

1st degree AV block

PR >0.20 s, same long PR every beat; every P conducts

2nd degree type I (wenckebach)

PR gets longer each beat until a QRS drops; problem at AV node

2nd degree type II (mobitz II)

pr constant, but some P waves do not conduct in a set ratio (2:1, 3:1) problem in bundles; more dangerous

3rd degree (complete) AV block

no P-QRS relationship; atria and ventricles beat independently

3rd degree junctional escape

above/at AV: narrow normal QRS, 40-60 bpm

3rd degree ventricular escape

below AV: wide PVC-like QRS, 20-40 bpm

bundle branch block (BBB)

wide QRS, 0.12 s or more

right BBB

rabbit ears RSR’ in v1/v2; right ventricle depolarizes late

left BBB

broad notched skyscraper R in v5/v6 (deep S in v1); left ventricle depolarizes late