Rhythms and Management (Chapter 3) Flashcards
Blockage of which coronary a. can result in MI and/or AV nodal block
RCA
Blockage of this coronary artery often leads to sudden cardiac death, earning it’s name as the “widowmaker”
LCA
Blockage of what artery leads to lateral wall infarct
Left circumflex a.
Blockage of what artery leads to posterior wall MI
RCA (most common) or left circumflex (if pt has a left dominant heart)
What is responsible for the ability of the cardiac myocytes to propagate impulses (i.e. what is responsible for conductivity)
Intercalated disks
Why can you not get tetanic contractions in myocardial cells
Absolute refractory period
The absolute refractory period last until about what point on an ECG
Midway through the T wave
When is the relative refractory period on an ECG
From the top of the T-wave to the end of the T-wave (i.e. the downslope)
What is the supranormal period?
Period right after the relative refractory period where the myocytes are more sensitive stimuli than normal
When is the supranormal period on the ECG
Right after the end of the T-wave (i.e. after the end of the RRP)
Intrinsic rate of the SA node
60-100 beats
What does the AV junction consist of
AV node and the non-branching portion of the Bundle of His
Intrinsic rate of the bundle of His
40-60
Intrinsic rate of the Purkinje fibers
20-40
What is the record of electrical activity b/w 2 electrodes
A lead
What leads make up the frontal plane
I, II, III (standard leads)
aVR, aVL, and aVF are called augmented leads
Lead that is right arm to left arm
Lead I (only one “L”)
Lead that is right arm to left leg
Lead II (2 “L’s”)
Lead that is left arm to left leg
Lead III (3 L’s)
Which frontal plane lead most closely follows the normal pathway of current in the heart
Lead II
General rule for which limb the + electrode is on in a lead
Whichever lead has the most L’s (e.g. III is left arm to left leg, so the + node is on the left leg (2 L’s))
Heart surface viewed by lead I
Lateral
Heart surface viewed by leads II and III
Inferior
Heart surface viewed by aVR
NONE
Heart surface viewed by aVL
Lateral
Heart surface viewed by aVF
Inferior
What horizontal leads monitor the interventricular septum
V1 and V2
What horizontal leads monitor the anterior heart surface
V3 and 4
What horizontal leads monitor the lateral heart surface
V5 and 6
What surface of the heart is not directly viewed by any leads on a standard 12 lead ECG
Posterior surface
15 lead EKG has what additional leads
V4R, V8 and V9
In a normally conducted beat, QRS complex mainly represents electrical activity of what
LV
What leads monitor the inferior heart wall
II, III, aVF
What leads monitor the septum
V1 and 2
What leads monitor the anterior wall
V3 and 4
What leads monitor the lateral wall
I, aVL, V5, V6
What is one horizontal unit on ECG a measure of
0.04 seconds
What is measure by the thicker horizontal lines on the ECG
.2 seconds (made up of 5 single unit intervals)
What does one vertical unit on an ECG measure
.1 mV
What does a thick line on the vertical axis measure
.5 mV (5 single unit intervals)
Normal Q wave is how long?
.04 second (one small box)
About how much vertical distance on the Q wave is considered abnormal
> 1/3 the height of the R wave
Normal duration of QRS complex
.11 s or less
QRS duration in an incomplete bundle branch block
B/w .10 and .12
Duration of QRS complex in a complete BBB
Greater than or equal to .12
From which lead should you measure the QRS complex width
Whichever has the longest duration and the most clear onset and end.
Wider QRS complexes mean what
Delay in conduction through ventricles
What does the U wave represent and where is it on an ECG
Represents Purkinje fiber repolarization and is after the T wave
What conditions may cause deviation in ST-segment
MI, myocardial injury, or infarction
ST depression in a pt with acute coronary syndrome (ACS) represents what
Myocardial ischemia
ST elevation in a pt w/ ACS represents what
Myocardial damage
What part of the ST segment are we most interested in looking at when looking for ST elevation or depression
Early portion next to the J-joint
Normal duration of PR interval
.12-.20
What does the QT interval represent
Total ventricular activity (Depol and repol)
What happens to the QT interval as the HR increases
QT interval decreases
Corrected QT intervals more than what time are considered high risk for life-threatening arrhythmias
> 0.5 s
What normal physiological event can mess with sinus rhythm
Breathing (can cause a respiratory sinus arrhythmia)
What happens to HR during inspiration
Increases
What happens to HR during expiration
Decreases
How can you tell if a sinus arrhythmia is due to breathing or not?
Have the pt hold their breath (if due to breathing it disappears)
Do sinus arrhythmias usually need treatment?
No, but if hemodynamic compromise is present (due to a slow rhythm) atropine may be indicated
When do tachycardias start to cause problems
When ventricular rate is >150 beat/min
When is a tachycardia considered unstable
Serious signs and symptoms w/ HR usually >150
What should you do in an unstable pt w/ a pulse and serious S&S due to tachycardia
Cardiovert!
What is considered tachycardia in an infant
> 200 beats/min