Relative refractory periods - ️️occurs towards the end of the T-wave when most
ventricular cells are repolarized and vulnerable to new stimuli; can lead to VT if PVC
lands during this time
Refractory = resistant
Supraventricular Tachycardia (SVT) - ️️§ regular but fast rhythm
§ rate ...
AHN 568 Unit 1
Relative refractory periods - ✔️✔️occurs towards the end of the T-wave when most
ventricular cells are repolarized and vulnerable to new stimuli; can lead to VT if PVC
lands during this time
Refractory = resistant
Supraventricular Tachycardia (SVT) - ✔️✔️§ regular but fast rhythm
§ rate 150-250
§ P wave merged with T wave
§ PRI variable & difficult to measure
§ QRSà typically narrow
§ Common causes: stimulants, electrolyte imbalance, hypoxia
Sinoatrial Node (SA node)
Rate?
Location & Area of intervention?
EKG? - ✔️✔️Natural pacemaker of the heart
Rate: 60-100 bpm
Location: Upper portion posterior portion of the Right Atrium near superior vena cava
EKG: represented as the P wave
Atrioventricular node (AV node)
Rate?
Location? - ✔️✔️A specialized mass of conducting cells located at the atrioventricular
junction in the heart. (back-up pacer of the heart
Rate 40-60 bpm
Location: Near the tricuspid valve
Bundle of HIS
Rate?
Location? - ✔️✔️pathway for electrical signals to be transmitted to the ventricles
Rate: 40-45 bpm
Location: partially in right atrium and upper portion of interventricular septum that
connects the AV node and 2 bundle branches
Purkinjie Fibers
Rate? - ✔️✔️hair-like fibers that spread out from bundle branches into the ventricles;
innervate myocardial cells directly; initiate ventricular depolarization
Rate: 20-40 bpm
Normal Conduction Pathway through the Heart - ✔️✔️SA node
Interatrial tracts
AV node
, Bundle of His
Bundle branches
Purkinje fibers
resting membrane potential - ✔️✔️Electrical charge of cardiac muscle cells at rest
Depolarization - ✔️✔️change in the electrical charge of a stimulated cell from negative
to positive by the flow of ions; Na+ allows for depolarization, except in AV node which
depends on the slow moving Ca2+
Repolarization - ✔️✔️recharging of a cell to its normal polarity; K+ allows for
repolarization
action potential - ✔️✔️as cardiac cells reverse polarity, the electrical impulse generated
during that event creates an energy stimulus that travels across the cell membrane
What ion causes contraction? - ✔️✔️Calcium
Phase 4 - ✔️✔️Phase 4: Resting State
Na+ and Ca2+ channels are closed; increase in K+ permeability to allow for a new cycle
Phase 0 - ✔️✔️Phase 0: Rapid depolarization
Opening of voltage-gated fast Na+ channels; cell fires to initiate transmission of
electrical impulse
Phase 1 - ✔️✔️Phase 1: Depolarization
Peak positive charge; K+ closes, Cl- enters to slow channels, slow Ca2+ channels open
Phase 2 - ✔️✔️Phase 2 Plateau
Opening of voltage gated slow Ca2+ channels and closing of some K+, some Na+
enters to maintain; membrane potential is maintained or plateaued
Phase 3 - ✔️✔️Phase 3 Re-polarization
Opening of voltage-gated K+ channels and closing of Ca2+ channels; K+ moves from
ICF to ECF
Refractory periods - ✔️✔️time from phase 0 until the repolarization of a myocyte or
when enough Na+ have recovered
Absolute refractory periods - ✔️✔️occurs with the early part of the T-wave when most
of the ventricle is depolarized and is "refractory" to new stimuli
Normal P Wave - ✔️✔️Measures: 0.5 - 2.5mm high
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