heart exam II arrhythmias

kms

arrhythmia

abnormality of cardiac rhythm

bradycardia

abnormally slow heart rhythm

tachycardia

abnormally fast heart rhythm

supraventricular arrhythmias

originates in atria or av node

ventricular arrhythmias

originate in his-purkinje system or ventricles

main causes of arrhythmias

altered impulse formation
altered impulse conduction
can be both

automaticity

spontaneous depolarization of cardiac conducting cells

pacemaker current (if)

phase 4 depolarization current

pacemaker current is activated by

hyperpolarization

main ions involved in pacemaker current

slow na⁺ influx

slow ca²⁺ influx
decreasing k⁺ efflux

role of na⁺/ca²⁺ exchanger

brings in additional na⁺ after ca²⁺ release from sr

sa node intrinsic rate

60–100 bpm

av node / bundle of his rate

50–60 bpm

purkinje fibers rate

30–40 bpm

what determines pacemaker rate

slope of phase 4 depolarization
threshold potential
maximum diastolic potential

steeper phase 4 slope means

faster depolarization → faster heart rate

more negative resting potential does what

slows conduction

less negative threshold does what

slows conduction

why sa node dominates

fastest depolarization suppresses others

how cardiac cells are connected

gap junctions via intercalated discs

resting membrane potential

myocardial/purkinje: ~ -90 mV
av node: ~ -60 mV

effect of adjacent cells on pacemaker cells

hyperpolarizes pacemaker cells
slows heart rate

decoupling cells causes

ectopic rhythms

sympathetic stimulation effect

increases if and ca²⁺ → faster threshold → ↑ heart rate

parasympathetic stimulation effect

decreases if and ca²⁺ → slower threshold → ↓ heart rate

escape beat

occurs when sa node fails → other pacemaker fires

escape rhythm

sustained takeover by latent pacemaker

enhanced automaticity causes

catecholamines
hypoxemia
ischemia
electrolyte imbalance
drugs

abnormal automaticity definition

injured cells spontaneously depolarize

early afterdepolarization (ead)

occurs during repolarization
can cause tachyarrhythmias

delayed afterdepolarization (dad)

occurs after repolarization
if threshold reached → new action potential

normal conduction

sequential depolarization from sa node

role of refractory period

prevents backward/repeated activation

functional block

cell still repolarizing

fixed block

damaged tissue

re-entry mechanism

impulse re-circulates in loop

when re-entry occurs

slowed conduction allows reactivation

accessory pathway definition

abnormal atria-ventricle connection

accessory pathway effect

bypasses av node → faster conduction

accessory pathway result

pre-excitation + reentry

sinus bradycardia definition

sa node < 60 bpm

causes of sinus bradycardia

aging
ischemic heart disease
cardiomyopathy
athletes (↑ vagal tone)

sick sinus syndrome

intrinsic sa node dysfunction

sick sinus syndrome features

bradycardia
may alternate with tachycardia

junctional rhythm

from av node
inverted (retrograde) p wave

ventricular rhythm

30–40 bpm
widened qrs

AV block (first degree)

pr interval
→ > 0.2 sec

pattern
→ every p wave has qrs

significance
→ usually benign

AV blocks (second degree)

definition
→ intermittent failure of conduction

features
→ dropped qrs
→ qrs may be widened

AV block (third degree)

definition
→ no communication between atria & ventricles

key finding
→ p waves and qrs independent

ventricles depolarize via
→ escape rhythms

sinus tachycardia

→ sa node >100 bpm

causes of sinus tachycardia

fever
hypoxemia
hyperthyroidism
anemia
hypovolemia

atrial premature beats

cause
→ ectopic atrial focus

ecg features
→ early abnormal p wave
→ normal qrs

if av node refractory
→ no qrs (blocked)

atrial flutter rate

180–350 bpm

atrial flutter mech

large reentry circuit

atrial fibrillation

rate
→ 350–600 bpm

ecg
→ no p waves
→ irregularly irregular

mechanism
→ multiple reentry circuits

PSVT (paroxysmal supraventricular tachycardia)

features
→ sudden onset/termination
→ rate 140–250 bpm
→ narrow qrs

most common type
→ avnrt

AVNRT

two pathways
→ fast pathway (long refractory)
→ slow pathway (short refractory)

mechanism
→ apb blocks fast pathway
→ signal goes down slow pathway
→ reenters fast pathway → loop

ecg clue
→ retrograde p waves

brugada syndrome

cause
→ sodium channel defect

risk
→ sudden death (vf)

wolff parkinson white

cause
→ accessory pathway

ecg findings
→ short pr interval
→ delta wave
→ widened qrs

ventricular premature beats (VPB)

definition
→ ectopic ventricular firing

ecg
→ wide qrs
→ no preceding p wave

patterns
→ bigeminy (every other beat)
→ trigeminy (every third beat)
→ couplets (2 in a row)
→ triplets (3 in a row)

causes
→ caffeine
→ hypoxia
→ electrolyte imbalance

gap junctions

allow current spread between cells

phase 4 slope

determines pacemaker rate

re-entry loop diagram meaning

impulse circles instead of stopping

accessory pathway diagram

bypasses av node → early ventricular depolarization

delta wave

early slurred upstroke in qrs