CARDIOLOGY Chapter 12 - Guyton Flashcards

1
Q

Mean QRS vector

A

+59 degrees is the avg. direction of vector during depolarization, means the apex of heart is positive with respect to base of heart

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2
Q

Axis for each standard bipolar lead and each unipolar limb lead.

A

Lead I axis is 0 degrees, b/c electrodes lie exactly in the horizontal direction; Lead II axis is about +60 degrees b/c electrodes lie on upper right corner of torso and lower left corner of leg; Lead III axis is +120 degrees; aVR axis is +210 degrees; aVF axis is +90 degrees; aVL axis is -30 degrees

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3
Q

Normal T wave

A

all three bipolar limb leads is positive, which is also the polarity of most of the normal QRS complex

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4
Q

Hypertrophy

A

Left ventricle (Left axis shift) caused by hypertension, aortic stenosis, aortic regurgitation, causes a slightly prolonged QRS and high voltage; Right ventricle (right axis shift) caused by pulmonary, hypertension, pulmonary valve stenosis, interventricular septal defect

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5
Q

Bundle branch block

A

left block causes left axis shift b/c right ventricle depolarizes much faster than left ventricle, cause prolonged QRS complex

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6
Q

Increased Voltages in Standard Bipolar Limb Leads

A

Sum of voltages of Leads I-III > 4mV it is considered high voltage EKG; caused by increased ventricular muscle mass (hypertension, marathon runner)

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7
Q

Decreased voltages in standard bipolar limb leads.

A

caused by cardiac muscle abnormalities, old infarctions cause decreased muscle mass, low voltage EKS, and prolonged QRS caused by conditions surrounding heart fluid in pericardium, pleural effusion, emphysema; caused by anterior-posterior rotation of apex of heart

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8
Q

Heart position

A

left shift - caused by expiration, lying down and excess abdominal fat; right shift - exact opposite (skinny, inspiration, standing up)

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9
Q

Prolonged QRS Complex

A

Caused by prolonged conduction of cardiac impulse through the ventricles; Normal QRS is btwn 0.06-0.08 secs, prolonged QRS is caused by cardiac hypertrophy, purkinje system block, or conduction block (if QRS exceeds 0.12 sec)

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10
Q

Unusual QRS complex

A

caused by local conduction blocks which may cause multiple QRS peaks

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11
Q

Axis of the Current of Injury

A

At end of S wave ventricles are fully depolarized (J point), difference between J point and T-P segment is Current of Injury, voltages are plot on the coordinates of 3 leads to determine electrical axis, negative end of vector will originate in the injured/ischemic area of the heart

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12
Q

Anterior and Posterior Infarctions

A

Chest leads determine if current of injury is anterior/posterior; if negative, chest lead is area of negative potential, indicates anterior lesion; if positive current of injury, chest lead indicates posterior lesion; negative end of current of injury vector point towards abnormal cardiac muscle

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13
Q

Recovery from Coronary Thrombosis

A

T-P segment shows a current of injury following acute coronary thrombosis; improves over several weeks when at rest; exercise may cause ischemia of this recovered area, resulting in a current of injury

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14
Q

T wave abnormalities

A

Ventricular repolarization usually occurs in the opposite direction as depolarization which causes an upright T wave in the 3 standard leads; prolongation of repolarization may change T wave axis; Left bundle branch block causes late depolarization and thus a late repolarization of the left ventricle; Mild ischemia particularly in the apex of the heart prevents apex from repolarizing first, inverting T wave; Digitalis toxicity prolongs depolarization in certain part of heart, causes a biphasic T wave

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