ECG Flashcards
The instrument used for recording electric activity of heart is …., paper obtained is ….. & speed of paper moving is …..
Electrocardiograph
Electricardiogram
25 mm/sec
Uses & importance of ECG
- Anatomical orientation of heart
- Relative sizes of atria & ventricles
- Heart rate & regularity
- The pacemaker & path taken by AP
- Mscle status esp ventricles.
Mention abnormalities diagnosed by ECG
Dysrhythmias, myocardial ischemia & infarction, electrolyte disturnbance & influence of drugs (digitalis)
P wave represents ….., the ascending limb is for ….., while the descending is for …… , its duration is …..
Atrial depolarization
Right atrial depolarization
Left atrial depolarization
0.1 sec
Q wave represents ….. from …to….
Depolarization of ventricular septum , left to right
R wave represents ………, while S wave represents ……
Activation of ventricular mycodium (mainly left) from endocardial to epicardial surfaces.
Depolarization of the posterior & posterobasal portion of left ventricle & pulmonary conus
The start of isoelectric line after QRS is called …..
J point
T wave represents ….., its duration is …..
Ventricular repolarization
0.16-0.25 sec
GR: In ventricles, epicardium is repolarized before endocardium
Because the high intraventricular pressure presses on subendocardial blood vessels leading to partial ischemia, which delays repolarization in the endocardiak myocardial cells.
GR: Venticular re & depolarization are both upwardly deflected
Because de. is from endocardium to epicardium, while re. is from epicardium to endocardium.
U wave may represent ……., it is promininet in …
Slow repolarization of papillary & Purkinje fibers
Hypokalemia
GR: QRS amplitude is greater than P amplitude
Due to larger & thicker ventricular wall compared to atrial
GR: Duration of QRS is shorter than P complex
Due to presence of rapidly conducting Purkinje fibers in the ventricles.
GR: Atrial repoalrization is not recorded by ECG
It is buried in the QRS complex
PR interval respresents ….
Its duration is ….
Prolongation indicates …..
The time for atrial depolarization (plateau) plus the time for conduction through the AV node
0.12-0.21 sec
An abnormality of the conduction pathway through the AV node
QRS duration represents ….
Its duration is …..
Its prolongation indicates ….
Intraventricular conduction
0.04-0.08 sec
Ventricular hypertrophy and ventricular ectopic focus de. depends on cell-to-cell conduction
Q-T interval indicates …..
Its duration is ……
Ventricular electrical systole, measure for ARP
0.34 TO 0.43 sec
GR: ST segment is isoelectric
Because it represents a time when the entire ventricular myocardium is depolarized
ST interval is elevated in cases of …..
Myocardial ischemia
…… represents the true isoelectric line of ECG
T-P segment
The right leg is connected to …. Because …..
Ground
It acts as an electrical earth to discount other electric currents not produced by the heart preventing interference
A negative electrode is always placed on ….., a positive electrode is always placed on …..
Right arm
Left leg
State Einthoven’s law
The magnitude of any deflection in lead II is equal to the summation of the magnitude of the same deflection in lead I and in lead III.
Einthoven’s law detects …..
Abnormal physical connection
Mention the role of augmented limb leads
They record the potential difference between an exploring electrode on RA, LA or LL respectively and an electrode obtained by connecting the other two limbs
aVR = VR - (VL+VF)/2
Mention the position of precordial leads
V1 : 4th intercistal space left of sternum
V2 : 4th intercistal space right of sternum
V3: between V2 & V4
V4: 5th intercostal space left midclavicular
V5: 5th intercostal space left ant axillary line
V6: 5th intercostal space midaxillary line
The normal direction of vector is ….
Average is …..
-30 to +110 degrees
+60 degrees
Mention causes of left & right axis deviation.
L: 1. Short obese individuals, anatomical shift to left 2. Left ventricular hyoertrophy 3. Left bundle branch block 4. Right ventricular extrasystole R: opposite
Enumerate mechanisms of arrhythmias
- Disorders of impulse formation
a. Altered normal automaticity
b. Triggered activity - Disorders of impulse conduction (eg, reentry)
Mention factors determining firing rate
Maximum diastolic potential
Threshold potential
Slope of phase 4 depolarization
Mention conditions in which myocardial cells can exhibit automaticity properties
Conditions that drive the maximum diastolic potential towards the threshold potential (i.e. increased excitability such as hyperkalemia & catecholamine excess).
Define afterpolarization
Membrane potential oscillation that occur during or immediately following a preceding AP which acts as a trigger.
Mention the cause of afterdepolarization and its effect if exaggerated
Caused by a variety of conditions that raise diastolic intracellular IC Ca conc which can trigger a new AP if they reach the stimulation threshold.
(eg, in ischemia due to decreased activity of active Ca uptake)
Describe acceleration-induced block.
Impulses are blocked at high rates of incomplete recovery of refractoriness. When an impulse arrives & tissue that is still refractory , it will not be conducted (blocked).