lab 10 electrocardiography and cardiovascular sounds II Flashcards
who introduced electrocardiography?
Willem Einthoven
what is the QRS complex?
it is associated with the excitation of the ventricular muscle mass
what is the first point of myocardial excitation?
left ventricle at the apex
what is the first vector?
septal activation
how long does septal activation take?
0.01 seconds
what are the characteristics of septal activation?
the septal vector is oriented from the left ventricle to the right ventricle because the left ventricular component starts earlier and involves a larger segment of myocardium
what is the second vector?
free wall activation
how long does free wall activation take?
0.015-0.025 seconds
what are the characteristics of free wall activation?
the free-wall vector is oriented from the left ventricular endocardium toward the left ventricular epicardium. although a similar activation occurs in the free wall of the right ventricle, the involvement of the larger muscle mass of the left ventricle results in the net force as described; the laterally directed components are approximately equal and opposite, thus they cancel
what is the third vector?
basal activation
how long does basal activation take?
0.005-0.01 sec
what are the characteristics of basal activation?
the base of the ventricle is activated by a vector moving in an apicobasilar direction
to explain the vector’s impact at surface electrodes, what must one consider?
- the orientation of the three vectors with respect to the surface electrodes’ lead axis
- the general determinants of the distantly recorded potentials in a volume conductor
what are the 3 planes? (XYZ)?
X: sinistrodextral, Y: craniocaudal. Z: dorsoventral
what is an orthogonal lead system?
a system that uses electrode positions so the lead axis is equivalent to one of the geometrical axes
what is an example of an orthogonal lead system?
V10, aVF, lead I
what is v10?
it is a unipolar lead with the positive electrode located over the 7th thoracic spinous process
what axis is the V10 equivalent to?
the Z (dorsoventral axis)
what is aVF?
the positive electrode is on the left hindlimb and the reference electrode is the combined right and left thoracic limbs
what axis is aVF equivalent to?
Y axis (craniocaudal)
what is is lead I?
it has the positive electrode on the left thoracic limb and the negative electrode on right thoracic limb
what is the lead I equivalent to?
the Z axis (sinistrodextral)
when is a positive deflection elicited?
when the wave of depolarization moves toward the positive electrode
when is a negative deflection recorded?
when the orientation is reversed so the depolarization moves toward the reference electrode
when does no deflection occur?
when the uncancelled vector is oriented at right angles to the lead axis
what is the recorded potential proportional to?
the magnitude of the net electrical vector and the proximity of the electrode to it
how can the relationship of the recording to the depolarization be summarized?
recorded potential=source potential/distance from source to recording electrode *cos (angle that vector makes with lead axis)
what species have a similar QRS to the dog?
dog, man, monkey, rat, cat
what species have a dissimilar QRS compared to the dog?
horse, goat pig, sheep, cow
what is the series of depolarizations in the horse, goat, pig, sheep, cow?
- initial depolarization of the subendocardial shell surrounding the apex of the left ventricle
- terminal depolarization of the middle and basilar thirds of the interventricular septum in an apico-basilar direction
- generalized depolarization of ventricular muscle mass without creation of a wave of depolarization
what is the main concept of measuring the mean electrical axis of the heart?
that you can consider the ventricular excitation as being represented by a single electrical vector
what is einthoven’s law?
lead I-lead II+ lead III=0
what is the main utility of Einthoven’s law?
to ascribe an angular orientation to the mean electrical axis
how many leads are required to plot the mean electrical axis?
2
what are the three basic methods for estimating the mean electrical axis using the three standard limb leads and three augmented leads?
- measure the algebraic sum of the QRS deflections in leads I, II and III and plot on a triaxial system
- find an isoelectric lead, the algebraic sum of the QRS deflections being zero
- choose the lead with the largest net QRS deflection
what is the normal range of the mean electrical axis in the dog?
40-100 degrees
if the mean electrical axis of the dog is greater than 100 degrees, what is this called?
right angle deviation
what is right angle deviation associated with?
right ventricular hypertrophy
by convension, a one centimeter deflection represents a potential of how much?
1 mV
what is the normal paper speed for small animals?
50mm/sec
what is the normal paper speed for large animals
25mm/sec
what are bipolar leads?
when both electrodes are sufficiently close to the heart to be influenced by it, this is called a bipolar lead system
what is lead I?
the potential difference is recorded between the left(+) and right forelimbs
what is lead II?
the potential difference is recorded between the left hindlimb (+) and right forelimb
what is lead III
the potential differnce is recorded between the left hindlimb (+) and the left forelimb
what are unipolar leads
unipolar leads (unaugmented) measure potentials betwen an exploring electrode in proximity to the potential source versus a distant reference electrode or versus a neutralizing reference
what are augmented unipolar limb leads?
they utilize the standard electrode placements with one electrode serving as the exploring electrode and the remaining two combined as the reference
what aVR
it is the right forelimb considered as positive with the other two as reference
what is aVL?
it is the left forelimb considered as positive with the other two as references
what is aVF
it is the left hindlimb considered as positive with the other two as references
what are precordial unipolar leads?
it is a unipolar lead with the reference as the central terminal of wilson where the limb electrodes are connected through 5000 ohm resistors to a single point which serves as a reference or electrical zero
how do you measure the mean electrical axis?
the positive and negative deflections in lead I and lead III are added. the perpendicular lines are then followed from the positive or negative point determined for each lead in the triaxial system. A line drawn from the triaxial system to the point of the intersected perpendicular lines gives the direction and relative magnitude of the mean QRS vector
what is the P-R interval?
the interval from the BEGINNING of the P wave to the BEGINNING of the QRS complex. it corresponds to the time taken for the excitation to spread from the SA node the beginning of the spread through the ventricular musculature
what is the P-R segment?
it is an isoelectric point measured from the END of the P wave to the BEGINNING of the first deflection away from baseline of the QRS complex
what is the QRS complex?
the Q wave is the first negative defleciton, the R wave is the first positive deflection. the S wave is a negative deflection occurring after a negative and//or positive R deflection
the length of the QRS measures the time for ventricular depolarization
what is the Q-T interval
it is the interval from the BEGINNING of the QRS to the END of the T wave and measures ventricular depolarization and ventricular repolarization. it approximates ventricular contraction
what is the S-T segment?
it is the period from the END of the QRS complex to the BEGINNING of the T wave. it corresponds to the plateau period of the ventricular myocardial action potential and is normally isoelectric or only slightly displaced from it.
what is percussion?
the elicitation of sounds from parts of the body by tapping with fingers or an instrument.
what is auscultation
the detection and study of sounds produced in the body
what causes sounds?
they result from a vibrating body causing vibrations or waves in the air, which, when impinging upon the ear, are perceived as sound.
what are tones?
sounds produced by regular oscillations causing a series of waves vibrating at a uniform rate
what does intensity depend upon?
the amplitude of vibration
what does pitch depend on?
the number of vibrations produced in a given period of time (frequency)
what are transients?
cardiovascular sounds of short duration
what are murmers
cardiovascular sounds of longer duration
what is a phonocardiogram?
the recording of the sounds from the heart
what is the first heart sound?
it occurs at the termination of atrial contraction and onset of ventricular contraction (closing of AV valves)
what is the second heart sound?
it is the closing of the semilunar valves
what is splitting
when the heart sound is split; it is more likely to occur with the second heart sound and during inspiration (the pulmonary lags the aortic) b/c increased negative thoracic pressure draws blood back to right ventricle and prolongs ejection phase
what is the third heart sound?
it is the sound occuring during diastole and is generally due to rapid inflow of blood, usually occurs during end of rapid filling phase when ventricle walls are less flaccid (more taut)
what is the fourth heart sound?
it is the sound produced by atrial systole
which sound is more intense in the dog and man?
the first sound
which sound is often more intense in the horse?
the second heart sound
is splitting common in healthy dogs?
no
is splitting of the second sound common in horses?
yes
what are examples of abnormal sounds?
ejection sounds
systolic clicks
gallop rhythms
what are ejection sounds?
sharp high pitched sounds that occur shortly after first heart sound when aortic and pulmonary valves open and is considered due to forceful ejection of blood into dilated great vessels
what are systolic clicks?
extra sounds that sound like clicking between first and second heart sound
what are gallop rhythms?
due to occurrence of first, second and another heart sound
what are murmurs?
cardiovascular sounds of longer duration
due to turbulent flow due to obstructions in path of blood flow
timing, intensity, pitch over each four valve regions should be noted
when is a stenosis of an AV valve heard?
in diastole
when is a stenosis of a semilunar valve heard?
in systole
when is an insufficiency in an AV valve heard generally
in systole
when is an insufficiency in a semilunar valve heard generally
in diastole
what is the characteristic of an AV valve stenosis?
decrescendo diastolic with a presystolic accentuation if atrium contracts; low pitched, rumbling, rare
what is the characteristics of an AV valve insufficiency?
pansystolic, medium pitched, common
what are characteristics of a semilunar valve stenosis
diamond shaped holosystolic; medium pitched, may be harsh; associated with heart worms; rare
what are the characteristics of semilunar valve insufficiency?
decrescedo diastolic; high pitched; uncommon
what are common non-valvular murmurs?
anemia
ventricular septal defect
patent ductus arteriosus (with left to right sjunt)
when is a murmur due to anemia heard?
during early systole;
when is a murmur associated with a ventricular septal defect heard?
during systole; varies in pitch; rough
when is a continuous murmur of patent ductus arteriosus heard?
the whole time
