Electrocardiogram Flashcards
What is the purpose of a 12 lead ECG?
to get 12 views of the heart and assess cardiac rhythm and diagnose the location, extent, and acuteness of myocardial ischemia and infarction and evaluate changes in activity
What are the electrode locations for the limb leads when taking an ECG?
Right Arm (RA)- infraclavicular fossa medial to the right deltoid Left Arm (LA)- infraclavicular fossa medial of left deltoid Right Leg (RL)- right side of abdomen (ground electrode) Left Leg (LL)- left side of abdomen below rib cage
What are the electrode placements of the chest for precordial leads of an ECG?
V1-4th intercostal space to right of sternum
V2-4th intercostal space to left of sternum
V3- midway between V2 and V4
V4- 5th intercostal space to left of midclavicular line
V5- left anterior axillary line at V4 level
V6- left midaxillary line at V4 and V5 levels
How many bipolar limb leads are there in a 12 lead ECG? How many augmented uni-polar limb leads? How many uni-polar leads?
3 bipolar limb leads
3 augmented uni-polar limb leads
6 uni-polar leads
Where is the positive and negative input for the bipolar limb leads in a 12-lead ECG?
Lead 1: Positive- left arm Negative- Right Arm
Lead 2: Positive- Left Leg Negative- Right Arm
Lead 3: Positive- left leg Negative- Left Arm
Where is the positive and negative input for the augmented uni-polar limb leads in a 12-lead ECG?
aVR: (+) Right Arm (-) Left arm and left leg
aVL: (+) Left Arm (-) right arm and left leg
aVF: (+) Left Leg (-) right arm and left arm
Where is the positive and negative input for the uni-polar precordial leads in a 12-lead ECG?
V1- (+) 4th IC space R of sternum (-) Central Terminal
V2- (+) 4th IC space L of sternum (-) Central Terminal
V3- (+) between V2 and V4 (-) Central Terminal
V4- (+) 5th IC space L of midclavicular line (-) Central Terminal
V5- (+) L ant axillary line at V4 level (-) Central Terminal
V6- (+) L midaxillary line at V4/V5 level (-) Central Terminal
What is the central terminal for the unipolar precordial leads?
the negative or reference input which is composed of a compound electrode formed by electrically combing the output of the LA, RA, and LL electrodes
What does the P wave on an ECG represent?
Atrial depolarization
What does the PR Interval on an ECG represent?
What is the normal duration of the PR interval?
time for atrial depolarization and conduction from the SA node to the AV node.
Normal duration is .12 to .2 seconds
What does the QRS Complex on an ECG represent?
What is the normal duration of the QRS complex?
Ventricular depolarization and atrial repolarization.
Normal Duration is .06 to .1 seconds
What does the QT interval on an ECG represent?
What is the normal duration of the QT interval?
time for both ventricular depolarization and repolarization
Normal Duration is .2-.4 seconds depending on HR
What does the ST Segment on an ECG represent?
Isoelectric period following QRS when the ventricles are depolarized
What does the T wave on an ECG represent?
Ventricular repolarization
What is normal sinus rhythm?
atrial depolarization begins in the SA node and spreads normally through the electrical conduction system with a HR between 60-100 bpm
What is sinus bradycardia?
sinus rhythm with a heart rate less than 60bpm
What is sinus tachycardia?
sinus rhythm with HR over 100bpm
What is sinus arrythmia?
a sinus rhythm but with beat-to-beat variations due to impulse formations being faster or slower
What is sinus arrest?
a sinus rhythm, except with intermittent failure of the SA node impulse formation or AV node conduction that results in an occasional absence of P or QRS waves
What are premature atrial contractions and how do they occur?
PACs are when the P wave is premature with an abnormal configuration
PACs occur when an out of place focus in the atrium initiates an impulse before the SA node
What is the clinical significance of premature atrial contractions?
PACs are very common and usually benign but can progress into Atrial flutter, Afib, or tachycardia
Typically can occur due to increased caffeine intake, stress, smoking, or alcohol or due to any type of heart disease
What is atrial flutter?
an ectopic very rapid atrial tachycardia with an atrial rate of 250-350bpm
On ECG the P waves usually have a saw-tooth appearance
What is the clinical significance of atrial flutter?
What are the signs and symptoms of atrial flutter?
usually occurs with valvular disease (especially mitral), ischemic heart disease, cardiomyopathy, HTN, acute myocardial infarction, COPD, and pulmonary emboli
SxS include palpitations, lightheadedness, and angina due to rapid HR
-stagnation of blood may predispose to thrombi in the atria
What is atrial fibrillation (Afib)?
How does it commonly appear on an ECG?
a common arrythmia where the atria are depolarized between 350 and 600 times a minute
ECG shows characteristically irregular undulations of ECG baseline with no discrete P-waves
What is the clinical significance of Atrial fibrillation?
What are the signs and symptoms of Afib?
- can occur in healthy hearts and in patients with coronary artery disease, HTN, and valvular disease
- stagnation of blood may predispose to thrombi in the atria
SxS include palpitations, fatigue, dyspnea, syncope, and chest pain
What is a 1st degree Atrioventricular (AV) block?
What is the clinical significance of this type of block?
PR interval is longer than .2 seconds but relatively constant from beat to beat
usually has no significance in change of cardiac function and PR interval may be longer due to many reasons including medications
What is a 2nd degree Atrioventricular (AV) block?
What are the two major types?
an AV conduction disturbance in which impulses between the atria and ventricles fail intermittently
2 major types are Mobitz type 1 block (Wenckebach block) and Mobitz type 2 block
What is the difference between a Mobitz type 1 block and a Mobitz type 2 block?
Mobitz 1- progressive prolongation of PR interval until one impulse is not conducted
Mobitz 2- consecutive PR intervals are the same and normal followed by nonconduction of one or more impulses. If heart rate is slow, cardiac output will decrease with the blocked impulse
Both types may progress to 3rd degree AV blocks
What is a 3rd degree Atrioventricular (AV) block?
What is the clinical significance of this type of block?
Also known as a complete heart block because all impulses are blocked at the AV node and none are transmitted to the ventricles which causes the atria and ventricles to be paced independently with atrial rate being higher than ventricular rate
- this is considered a medical emergency and requires a pacemaker
- patient may faint due to low ventricular rate
- common causes include acute MI, heart surgery, digitalis, or a degenerative change of the conduction systems
What is a premature ventricular complex?
How do they normally appear on an ECG?
A type of ventricular arrhythmia due to premature depolarization in the ventricles due to an ectopic focus
On ECG the p-wave us usually absent and the QRS complex has a wide an aberrant shape
What is the difference between bigeminy and trigeminy PVCs?
Bigeminy: normal sinus umpulse is followed by a PVC
Trigeminy: PVC occurs after every two normal sinus impulses
What is the clinical significance of a PVC?
usually benign and asymptomatic but patient can have palpitations due to PVC, it is a very common arrythmia which occurs in both healthy and diseased hearts
common causes include anxiety, caffeine, stress, smoking, and all forms of heart disease
What is ventricular tachycardia?
How does it typically present on an ECG?
3 or more consecutive PVCs at a ventricular rate of over 150bpm
P waves are absent and QRS complexes are wide and aberrant on ECG
What is the significance of a ventricular tachycardia that lasts over 30 seconds?
this is a life threatening arrhythmia that requires immediate medical attention due to patients no being able to maintain an adequate blood pressure and eventually become hypotensive
What are common causes of ventricular tacchycardia?
MI, cardiomyopathy, and valvular disease
What is ventricular fibrillation?
How does it appear on an ECG?
ventricles do not beat in a coordinated fashion but fibrillate or quiver asynchronously and ineffectively which causes there to be no cardiac output and renders patient unconcious
ECG shows characteristic fibrillatory waves with an irregular pattern that is either coarse or fine
What is the clinical significance of ventricular fibrillation?
What are the common causes of V-fib?
a lethal tachyarrhythmia requires immediate defibrillation
MI, cocaine use, or heart disease of any kind
What can a depressed ST segment on an ECG be a sign of?
subendocardial ischemia (could also be due to digitalis toxicity or hypoalkemia)
What can an elevated ST segment on an ECG be a sign of?
earliest sign of acute transmural infarction and can also indicate a benign early repolarization pattern in a normal heart
What would qualify as a significant elevation or depression of the ST segment on an ECG?
1+ mm deviation from the isoelectric baseline
What might a Q wave that is longer than .04 msec and larger than 1/3 the amplitude of the R wave indicate?
a key marker of infarction that signifies the loss of positive electrical voltages due to necrosis
What does an inversion of the T wave represent?
a key sign of MI which occurs hours or days after the infarction as a result of the delay in repolarization produced by the injury
May also occur with right and left bundle branch blocks, after a CVA, and appear as a normal T wave pattern in children
