Flashcards in EKG Conference Deck (28)
The action potential duration is represented by what part of the EKG?
- usually 230-450 msec
What occurs during the P-R interval?
Depolarization of Atria, Bundle Branches, Purkinje & Bundle of His
What is the term for the following:
1. Area of EKG that includes a waveform
2. No waveform
When does the SA node depolarize on the EKG?
Before the P wave
When is the plateau of the action potential, as reflected on the EKG?
S-T Segment (no waveform)
If all the QRS complexes were tall, how would this be seen clinically?
HYPERTROPHY of the ventricles (in football players for example)
- seen via XRAY --> hypertrophy of the ventricles
Everyone has the same Q-T interval. True or False?
NO FIXED QT INTERVAL SINCE EVRYONE HAS A DIFFERENT BASE HR
When does depolarization of the ventricles occur?
How is the speed of the Action Potential reflected on an EKG?
the timing of QRS --> narrow QRS = fast AP
slurred QRS = slow AP
What are the slow activating AP of the heart? When are these cells depolarized on the EKG?
1.Sa and AV node
1. Before the Pwave
2. During the middle of the p wave = AV Nodal (activated before atrial depolarization)
How does the His Bundle enter the left and right bundle branches?
through the SEPTUM
- first place depolarization of the heart is spread (depolarization starts here as well)
The EKG provides info on contractile ability and strength of the heart. True or False
- but we can infer from the EKG various changes
What si the value in seconds of one small box? A large box?
Small - 0.04 seconds
Large - 0.2 seconds
How do you calculate HR on EKG?
300/ # of boxes between each QRS
What is the main change during a tachycardia?
- diastole is decreased, so with length-interval relationship the systole is shortened so that diastole can be prolonged a little to allow increases filling
What are the values for the following
1. P-R Interval
3. Q-T interval
1. 120-200 (.12 -0.2)
2. 70-100msec (0.07-0.1)
3. 230-450 (0.23-0.45)
4. cycle length less than 0.6 seconds (600 msec) & greater than 100 beats/min
5. cycle length greater than 1 second (1000 msec) & les than 60 beats/min
Of the precordial leads, which is strongest and why?
- closest to left ventricle so positive deflection is largest
Describe the location of the precordial leads.
V1 - 4th intercostal space at the right sternal border
V2 - 4th intercostal space at the LEFT sternal border
V3 - is placed halfway between V2 and V4
V4 - 5th intercostal space at the left midclavicular line
V5 - same level as V4 at the left ANTERIOR axillary line
V6 - same level as V4 at the left midaxillary line
V1 and V2 = septal leads. Electrical activity of the inter-ventricular septum is best measured in these leads.
V3 and V4 = anterior leads. Electrical activity of the anterior (front) wall of the left ventricle is best measured in these leads.
V5 and V6 = left precordial or lateral precordial leads.
A notched QRS is often the sign of what?
Bundle Branch block
-As conduction through the myocardium is slower than conduction through the Bundle of His-Purkinje fibres,
- since NOT conducting through His-Prukinje system (and through muscle) - the action potential is slower and QRS is widened!!
-The QRS complex often shows an extra deflection which reflects the rapid depolarisation of the left ventricle followed by the slower depolarisation of the right ventricle.
Can an EAD or DAD be seen on an EKG?
- no membrane potentials seen directly on EKG
What is the mnemonic to distinguish Left & Right bundle branch block?
A mnemonic to distinguish between ECG signatures of Left bundle branch block (LBBB) and right, is WiLLiaM MaRRoW; i.e., with LBBB, there is a W in lead V1 and an M in lead V6, whereas, with RBBB, there is an M in V1 and a W in V6.
What are the:
1. Inferior Leads
2. Lateral Leads
4. Antero septal
1. Leads II, III, avF
2. V5, V6, avL, I
3. V1-V2 = septal
V3-V4 = anterior
In PVC, what has changed due to changes in AP?
- Ca handling
After a PVC, will arterial pressure be higher or lower? Why does a PAUSE occur?
HIGHER than normal
= increased after load
- SA blocked in AV node since ventricle is still in refractory period --> recovers after this pause
- increase contractility due to PESP
What is the last part of the heart to be activated? The first?
1. Epicardial Surface (endo to epi)
Why does repolarization cause a positive waveform? Where does repolarization start?
1. Vector of depolarization is in the same direction as the vector of depolarization
(even though it is an opposite electrical event)
2, EPICARDIAL SURFACE
What Repolarizes first, epicardium or endocardium?
- shorter AP & quicker depolarization because there is a K+ current
- epicardial cells have more iTo
= shorter AP as a result