ECG Flashcards
waht is a wave?
a deflection, positive or negative, away from the isoelectric line
what is a complex?
several waves
a segment?
a straight line between waves/complexes
Interval?
a segment and a wave
Timing on ecg?
Vertical lines
1 small box = 0.04sec
1 large box = 0.2 sec
voltage on ecg?
horizontal lines
0.10mV=1small box
Normal duration of
PR
QRS
QT
cQT
PR: 120-200 ms (3-5ss)
QRS <=120ms (3ss)
QT <= 0.5 RRinterval
cQT=QT/ (square root from RR interval)
Heart rate calculation
No. Of beats in 300 large squares = beats in 1 min
300/(number of large squares between two R waves)
OR (number of QRS) x 6 in the rhythm strip
1500 small squares = 1 minute
1500/(number of small squares between two R waves)
a broad T wave means what?
A broader T wave ↔ ↑ heterogeneity of repolarization among cardiac muscle cells →it takes longer (temporal dispersion of refractoriness). This is the substrate for re-entry.
QT interval:
what does it measure and what does its prolognation mean?
A long QT interval (a measure of the duration of repolarization) may identify the patient at risk for ventricular arrhythmias and sudden death.
The QT prolongation of hypocalcemia has somewhat less risk. This is the only cause of QT prolongation where the duration of the T wave is not prolonged—a normal T wave just occurs later.
Upward or downward QRS complexes and concordant T waves in which leads?
In the young:
Upward & concordant: **I, II, III, aVF, V3-V6 **
DOwnward & concordant: aVR, V1, V2
In older adults, T waves are upward in V2 and sometimes V1 despite the fact that QRS are downward.
Physiological Q waves represent what?
Normal parameters?
Physiological Q waves represent the upwards depolarisation of the septum (in II, II, aVF)
In V6, V5 leads, the Q wave represents Lefto to Right septal depolarisation.
Normally, q wave is <0.04s (<1ss wide), no deeper than 25% of subsequent R wave.
Left Bundle Branch distribution and actions
Left bundle branch (LBB) branches into:
- Left anterior fascicle (LAF).LAF depolarises ant & lat walls of LV.
- Left posterior fascicle (LPF).
LPF depolarises the post & inf surfaces of LV simultaneously. - Septal branch
Normal cardiac axis
Normal cardiac axis – leads I,II, II have positive QRS complexes.
Normal cardiac axis - -30˚ to 90˚, if the axis lies beyond aVL (-30˚) → left axis deviation (LAD).
If beyond aVF (90˚) →right axis deviation (RAD).
Left Axis Deviation due to & appearance:
due to LAF bkock
Left anterior descending artery pathology (ischemia, infarction),
LVH,
cardiomyopathy.
As the axis moves towords the left, III begins to delelop s wave, even further, lead II will also develop an s wave. Lead I retains a stron r wave At the limit of normality, the axis lies at a VL = lead II is isoelectic (r wave= s wave).
In the LAD: negative leads II & III, strongly positive – lead I
Right axis deviation due to
due to LPF block usualy, diffuse ischemia/infarction, cardiomyopathy. Local ischemia rarely ahs a significant effect because of extensive anastomosis of blood supply.
Loss of a large part of LV myocardium due to MI (left lateral infarction), shifts the axis to the right and vice versa.
QRS complexes in LAD & RAD
In both LAD and RAD – QRS complexes are wider (but still within normal range) due to a slight delay of depolarisation in the affected area.
DIagnostics of LVH
Sokolow-Lyon: S wave in V1 + R wave in V5 or V6 (whichever higher) ≥3.5mV
OR R wave in V5 or V6 > 2.3mV
Cornell: R in aVL + S in V3 > ♂2.8mV or ♀2.0mV
RVH diagnostics
R wave > 7ss in lead V1
or
R:S ratio >1 in V1 suggests RVH.
In what lead is P wave normally negative?
aVR
Normal P wave measurments
Normal Pwave is
<2.5ss (0.11s)
and
<2.5mm amplitude.
RA enlargement
RA enlarges downward and to the right → amplitude of P wave↑ (>2.5mm (2.5 ss) in II, III, AVF) in inferior leads, but the width is still normal.
LA enlargement
LA enlargement →prolongation of P wave (> 2.5ss). Also, increased asynchrony results in notched P wave (two peaks = P mitrale). If the peaks are >0.05s (1ss) apart, it is indicative of LA enlargement. May produce a negative deflection after a P wave in V1 (>1ss in width and depth)
