Cardiac Dysrhythmias Notes – Cardiovascular Health Cardiac Dysrhythmias (Ch 26, pp. 692-728)

lOMoARcPSD|20734855




Cardiac Dysrhythmias


Notes – Cardiovascular Health Cardiac

Dysrhythmias (Ch 26, pp. 692-728)

, lOMoARcPSD|20734855




Cardiac Dysrhythmias 1

Notes – Cardiovascular Health Cardiac

Dysrhythmias (Ch 26, pp. 692-728)

Dysrhythmias

• Disorder of the formation or conduction (or both) of the electrical
impulse within the heart
• Can cause disturbances of HR, heart rhythm, or both

Influence on Heart Rate and Contractility

• Sympathetic nerve fibers (aka adrenergic fibers) are attached to heart
and arteries
o Positive chronotropy: stimulation of the sympathetic nervous
system increases HR
o Positive dromotropy: stimulation of the sympathetic nervous
system increases conduction through the AV node
o Positive inotropy: stimulation of the sympathetic nervous
system increases the force of myocardial contraction
o Sympathetic stimulation constricts peripheral blood vessels  increases
BP
o Decreases sympathetic stimulation leads to dilation of arteries  lowers
BP
• Parasympathetic nerve fibers are also attached to heart and arteries
o Negative chronotropy: parasympathetic stimulation decreases HR
o Negative dromotropy: parasympathetic stimulation decreases
AV conduction
o Negative inotropy: parasympathetic stimulation decreases the force
of myocardial contraction
• THUS, manipulation of the autonomic nervous system may increase or
decrease the incidences of dysrhythmias
o Sympathetic stimulation: exercise, anxiety, fever, catecholamine
administration (e.a., dopamine (Intropin), aminophylline,
dobutamine (Dobutrex))  may increase dysrhythmias incidences
o Decreases sympathetic stimulation: rest, anxiety reduction (meditation,
therapeutic communication), beta-blockers  may decrease incidences of
dysrhythmias

, lOMoARcPSD|20734855




Cardiac Dysrhythmias 2




FIGURE 26-1 • Relationship of electrocardiographic (ECG) complex, lead system, and
electrical impulse. The heart conducts electrical activity, which the ECG measures and shows. The
configurations of electrical activity displayed on the ECG vary depending on the lead (or view) of
the ECG and on the rhythm of the heart. Therefore, the configuration of a normal rhythm tracing
from lead I will differ from the configuration of a normal rhythm tracing from lead II, lead II will
differ from lead III, and so on. The same is true for abnormal rhythms and cardiac disorders. To
make an accurate assessment of the heart’s electrical activity or to identify where, when, and
what abnormalities occur, the ECG needs to be evaluated from every lead, not just from lead II.
Here the different areas of electrical activity are identified by color. RA, right arm; LA, left arm;
SA, sinoatrial; AV, atrioventricular; LL, left leg.

, lOMoARcPSD|20734855




Cardiac Dysrhythmias 3

Electrocardiogram

Obtaining and Electrocardiogram

• 12-lead ECG: 6 electrodes on chest, 4 on limbs
o place electrodes of limbs on not-bony areas and areas with without
significant movement
o leads I, II, III, aVR (augmented voltage right arm)
o aVL (augmented voltage left arm)
o aVF (augmented voltage left foot/leg)
o V1-6 (precordial leads)

FIGURE 26-2 • ECG
electrode placement. The
standard left precordial leads are
V1—fourth intercostal space, right
sternal border; V2—fourth
intercostal space, left sternal
border; V3—diagonally between
V2 and V4; V4—fifth intercostal
space, left midclavicular line; V5
—same level as V4, anterior
axillary line; V6 (not illustrated)—
same level as V4 and V5,
midaxillary line. The right
precordial leads, placed across the
right side of the chest, are the
mirror opposite of the left leads.
RA, right arm; LA, left arm; RL,
right leg; LL, left leg.