Chapter 11 - Guyton Flashcards
P wave
< 2.5 mm tall and < 0.12 sec long, immediately precedes atrial contraction (wider would signify longer duration for atria to depolarize)
PR interval
0.12 - 0.20 sec long (normal value of 0.16 sec), this time is needed for the ventricles to fill with blood!
QRS complex
up to 0.10 sec, immediately precedes ventricular contraction
T wave
positive when QRS positive, ventricles recover from depolarization (.25-.35 seconds after depolarization), ventricular repolarization
Why can atrial repolarization not be seen on the ECG?
masked by the QRS complex
QT interval
0.37 sec for men and 0.40 for women, this represents the time of ventricular contraction, heart rate can be determined with the reciprocal of the time interval between each heartbeat
How can you calculate HR with the ECG?
HR = 60 sec / R-R interval = BPM, usually take average from 3 cycles
Explain the flow of electrical current in the heart?
ventricular depolarization starts at the ventricular septum and the endocardial surfaces of the heart, average current flows positively from the base of the heart to the apex, at the end of depolarization the current reverses from 1/100 of a second and flows toward the outer walls of the ventricles near the base (S wave)
Lead I of Bipolar Limb Leads
negative terminal of the ECG is connected to the right arm and the positive terminal is connected to the left arm
Lead II of the Bipolar Limb Lead
negative terminal of the ECG is connected to the right arm and the positive terminal is connected to the left leg
Lead III of the Bipolar Limb Lead
negative terminal of the ECG is connected to the left arm and the positive terminal is connected to the left leg
Q wave
when initial inflection is negative
R wave
first positive deflection
S wave
negative deflection following the R wave
QS
all negative
R prime
second positive inflection that occurs after the S wave, only in abnormal ECGs
Use of lower case in ECG?
to notate an inflection that is not as strong
Einthoven’s Law
electrical potential of any limb equals the sum of the other two (I + III = II)
Chest (Precordial) Leads
V1 - V6, very sensitive to electrical potential changes underneath the skin
Augmented Unipolar Limb Leads
aVR (+ electrode right arm, - electrode left arm), aVL (+ electrode left arm), aVF (+ electrode left leg)
P pulmonale
Right atrial enlargement/abnormality - we would expect a large P wave > or = 2.5mm tall (no change in duration) in II, III, AVF, V1
P mitrale
Left Atrial Enlargement, wide P wave > 0.12 sec, amplitude normal or increased
Right Ventricular Hypertrophy
R wave > S wave in right Chest Leads (V1 or V2), Right Axis Deviation, Right Ventricular Strain Pattern, T wave inversions, Main characteristic: too much voltage to the right hand side
T wave inversions
T waves usually tend to go in same direction as QRS complex, If not, it is considered a strain pattern (or T wave inversion)
Left Ventricular Hypertrophy
Horizontal or Left Axis Deviation; This criteria tends not to be universally used; Person who can run a sub 5 min mile may present with this type of EKG
Right Bundle Branch Block (RBBB)
Wide QRS Complex, RSR’ in V1 and V2 often with ST-T changes
Left Bundle Branch Block (LBBB)
Wide QRS complex with broad or notched R wave in V5, V6, I, Loss of normal septal R wave in V1, Loss of normal septal Q wave in V6
Left Anterior Hemiblock (LAHB)
QRS complex < 0.12 sec + QRS axis > -45 degrees
Left Posterior Hemiblock (LPHB)
QRS complex < 0.12 sec + QRS axis > +120 degrees
Transmural MI
Q wave MIs, depolarization is completely blocked, damaged cardiac muscle remains partly or completely depolarized the entire time, injured muscles emit negative charges throughout each heartbeat, causes of current of injury:
local ischemia, mechanical trauma, infection
Subendocardial MI
Non Q wave MIs, subendocardial layer is vulnerable to ischemia associated with: angina pectoris, subendocardial infarction
Common ECG changes.
ST segment depression in the anterior or inferior leads, T-wave inversion, down-sloping into the T-wave is abnormal (“J-point”), up-sloping is normal
changes can be localized in the inferior leads
Acute Phase MI
S-T elevation; tall, positive (hyperacute) waves
huge
Evolving Phase MI: next day
Deep T wave inversions in leads showing S-T elevation, Development of significant Q-waves
Resolving Phase (Old MI)
significant Q waves appear, Partial or complete regression of ST-T changes
Sinus Bradycardia
HR < 60bpm, often seen in trained people, SA node is beating slow
Sinus Tachycardia
HR > 100 bpm
Atrial arrhythmias
PACman (premature atrial conduction), premature beat due to refractory period in SA node, occurs either with or without conduction, usually P wave present, compensatory pause
Premature Junctional Beat (PJC)
beat from AV junction, Premature beat usually without P wave, Depolarized by the atria before it reaches its critical threshold
Junctional Escape Beat
Beat from AV junction when normal pacemaker (SA node) fails, usually NO P wave, different from PJC in the R-R interval (much longer)
PVCs
premature before the next normal beat is expected
QRS wide; T wave and QRS are in opposite directions, compensatory pause, R on T phenomenon, couplets, Bigeminy (PVC-normal cycle-PVC-normal cycle), Trigeminy
SVT
3 or more consecutive PACs, no P-wave present
Atrial flutter
atrial stimulation rate ~ 300 bpm, flutter waves present, represented by ratio of atrial beats: vent. beats, forces AV junction to become pacemaker for ventricles
Atrial fibrillation
stimulated at very rapid rate, up to 600 bpm, presence of f waves or fib. waves, forces AV junction to becomes pacemaker for ventricles
Junctional Escape Rhythm
starts with junctional escape beat and continues to be paced by AV junction, 40-60 bpm, QRS and T-wave are normal
Accelerated Junctional Rhythm
Accelerated junctional rhythm has 60-100 bpm; Junctional tachycardia has 101-180 bpm
Ventricular Tachycardia
3 or more PVCs in a row
Ventricular Fibrillation
presence of f waves, fine or coarse fibrillation
Asystole
ya dead bro
1st Degree AV Heart Block
PR interval is prolonged (>0.2 sec)
2nd Degree AV Heart Block
mobitz 1 (Wenkebach): progressive lengthening of the PR interval until a beat is dropped; mobitz 2: nonconducted sinus P wave without progressive prolongation of PR interval
3rd Degree AV Heart Block
P waves are present; atrial rate faster than the ventricular rate; P waves bear NO relation to QRS; PR intervals variable
Wolff-Parkinson-White Syndrome
QRS complex widened; PR interval shorted; Appearance of delta wave; Often surgically repaired and relatively common