ECG and Dysrhythmias

SA node

located in the right atrium next to the superior vena ceva. It beats at 60-100bpm and it sets the heart rate

intermodal pathways

pass on the signal from the SA node and cause atrial contraction

AV node

located in the right atrium next to the lower septum and the tricuspid valve. It beats at 40-60bpm and strengthsns the signal of the SA node by slowing down the passing of the signal from the atria to the ventricles allowing for proper atrial contraction and ventricular dystole

Bundle of His

located in the ventricular septum, it splits into the right and left bundle branches. It beats at 40bpm and is not a pacemaker. It just passes the signal on

Purkinje Fibers

located in the ventricular muscle. These cells cause the myocardium to contract. Ventricular systole occurs once the signal reaches here

phase 0 of conduction

sodium channels open and sodium enters the cell. The membrane potential becomes positive. this is the depolarization phase

phase 1 of conduction

potassium begins to leave the cell and the membrane potential goes to zero

phase 2 of conduction

calcium enters the cell at the same rate that potassium leaves. It is a plateau phase

phase 3 of conduction

Calcium channels close but potassium continues to leave the cell. The membrane potential becomes negative. This is the repolarization phase

phase 4 of conduction

The cell is at rest. Sodium is outside the cell, potassium is inside. Membrane potential is -90

phase 0-the middle of phase 3 of conduction

the full refractory period in which there can’t be a reaction to cause electrical conduction

the second half of phase 3 of conduction

partial refractory period. Here if there is a strong enough stimulant the cell can go into early depolarization which leads to dysrhythmias

V1

ECG lead at intercostal space 4, right border of sternum

V2

ECG lead at intercostal space 4, left border of sternum

V3

ECG lead between V2 and V4

V4

ECG lead at intercostal space 5 on the midclavicular line

V5

ECG lead at the same height as V4 on the anterior axillary line

V6

ECG leaf at the same height as V4 on the midaxillary line

0.2 seconds

on the ECG how much time passes over 1 big square

P wave

represents atrial depolarization and moving of conduction from the SA node through the atria

QRS complex

represents ventricular depolarization and atrial repolarization. It is usually 0.12 seconds long

Q wave

negative wave that represents depolarization of the ventricular septum

R wave

positive wave that representsv depolariation of the ventricles

S wave

negative wave that represents depolarization of the ventricular base

T wave

positive wave representing repolarization of the ventricles

U wave

usually isn’t visible on the ECG. It represents repolarization of the purkinje fibers

PR interval

represents time from the SA node stimulation to just before ventricular depolarization

0.12-0.2 seconds

normal length of PR interval

ST segment

represents the beginning of ventricular depolarization. It is on the isoelectric line

QT interval

represents the total time of ventricular depolarization and repolarization

longer, shorter

the QT interval is _____ in bradycardia and _____ in tachycardia

0.32-0.4 seconds

normal length of QT interval

P-P interval

shows regularity of atrial conduction

R-R interval

shows regularity of ventricular conduction

methods to measure HR on the ECG

300 divided by number of large squares in the R-R interval

or

10 times the number of R-R intervals in 6 seconds (30 large squares)

the rhythm is not from the SA node

what does it mean if there is no P wave before the QRS

P pulmonale

pointy P wave that means there is too much pressure on the right ventricle

P mitrale

a second hump in the P wave due to hypertrophy of the left atrium

AV block

an elongated PR interval is a sign of what?

diversion of conduction to a different pathway

a shortened PR interval is a sign of what?

pericarditis

a lowered PR interval is a sign of what?

ventricular conduction

if the QRS complex is longer than 0.1 seconds this means there is damage to ______

fibrosis, VT, and acessory pathway

causes of an elongated QRS

acute or old MI

a deep or widened Q wave is a sign of what?

causes of elongated QT interval

MI, AV block, myocarditis, hypothermia, hypokalemia, hypomagnesiumia, myocardial and antipsychotic medications

MI, pericarditis, and LVH

causes of elevated ST interval

ischemia or reciprical prolapse in MI

causes of ST prolapse

ischemia or a PE

a negative T wave is a sign of what?

hyperkalemia

a sharp T wave is a sign of what?

ischemia

mismatch between the oxygen need in the muscles and what is being provided. It is seen as ST prolapse on the ECG

infarction

cellular damage due to lack of blood flow and necrosis. IT is seen as ST elevation on the ECG

sharp T wave and ST elevation

signs of the beginning of an MI on the ECG

pathological Q wave and upside down T wave

signs of a developing MI on an ECG

permanently deep Q wave with normal ST and T

signs of an MI that occured a month before on the ECG

V1, V2, V3, V4

an anterior MI can be seen on which leads?

V1, V2

a septal MI can be seen on which leads?

aVL, V5, V6, I

a lateral MI can be seen on which leads

II, III, aVF

an inferior MI can be seen on which leads?