EKGs

Question 1

What are common causes of a wide QRS complex?

Answer 1

Bundle branch block

Fascicular block

Pacing

Pre-excitation / WPW

Drug-induced

Question 2

if electrical activity has to travel outside of the ventricular conduction system, this makes the ____ wide.

Answer 2

QRS

Question 3

What EKG findings are characteristic of a right bundle branch block?

Answer 3

Prolongation of QRS to >120ms

rSR’ pattern or notched R wave in V1

Wide S wave in Lead I and V6

• (if this same pattern exists but the QRS is between 100-120ms, this is an incomplete RBBB. )*
• (Secondary T wave inversions in the right precordial that show a dominant R’ (V1-3)*

Question 4

Findings in V1 with RBBB:

Answer 4

rSR’ pattern or notched R wave

Question 5

Findings in V6 with RBBB:

Answer 5

Wide S wave

Question 6

What are potential clinical causes of a RBBB?

Answer 6

(Normal in ~3%)

Organic heart disease

• Atrial septal defect
• Pulmonary hypertension
• Valvular lesions

Degenerative changes in conduction system

Chronic coronary artery disease

Pulmonary embolism

Question 7

What EKG findings are characteristic of a LBBB?

Answer 7

Prolongation of QRS to >120 ms

rS or QS wave in V1

Broad and notched or slurred R wave in Lead I and V6

Absence of Q waves in Lead I and V6

• (if same pattern but QRS is between 100-120ms = incomplete LBBB)*
• (T wave changes opposite to the major QRS deflection)*

Question 8

What are potential clinical causes of a LBBB?

Answer 8

Organic disease

• Hypertensive heart disease
• Coronary artery disease
• Cardiomyopathy
• Valvular heart disease (aortic stenosis)

Degenerative changes in conduction system

Question 9

Findings in V1 with LBBB:

Answer 9

rS or QS wave in V1

Question 10

Findings in V6 with LBBB:

Answer 10

Broad and notched or slurred R wave

Absence of Q waves

Question 11

The left anterior fascicle is ____(superior/inferior) and _____ (leftward/rightward).

The left posterior fascicle is ____(superior/inferior) and _____ (leftward/rightward).

Answer 11

The left anterior fascicle is SUPERIOR and LEFTWARD.

The left posterior fascicle is INFERIOR and RIGHTWARD.

Question 12

EKG findings of a Left Anterior Fascicular Block:

Answer 12

(Look at limb leads)

QRS width less than 120ms (unless coexistant RBBB)

QRS axis is < -45 or -30 degrees (leftward shift)

qR in aVL

rS in aVF

Question 13

EKG findings of a Left Posterior Fascicular Block:

Answer 13

Limb leads

QRS width less than 120 ms unless coexistant with RBBB

Axis >120 degrees (right shift)

rS in aVL

qR in aVF

Rare - need to rule out other causes of right axis deviation

Question 14

A right axis shift might suggest a _____ block, whereas a left axis shift might suggest a ____ block.

Answer 14

A right axis shift might suggest a left posterior fascicular block, whereas a left axis shift might suggest a left anterior fascicular block.

Question 15

An isolated fascicular block is usually _____, although it may indicate underlying _____.

Answer 15

An isolated fascicular block is usually insignificant, although it may indicate underlying heart disease.

Question 16

When a fascicular block is combined with a _____, this is known as a bifascicular block.

Answer 16

When a fascicular block is combined with a RBBB, this is known as a bifascicular block.

Question 17

When a fascicular block is combined with a RBBB, this is known as a _______.

Answer 17

When a fascicular block is combined with a RBBB, this is known as a bifascicular block.

Question 18

If a patient with a bifascicular block begins having symptoms (e.g. syncope), theu may need a _____.

Answer 18

pacemaker

Question 19

What problems might necessitate a pacemaker?

Answer 19

Symptomatic bradycardia due to dysfunction of:

• sinus node,
• AV node, or
• infranodal system

Question 20

This EKG tracing suggests what about the patient?

Answer 20

They are being ventricularly paced

Question 21

What is structurally abnormal in a WBW patient?

Answer 21

There is a bypass tract present between the atria and ventricles. This allows electrical activity to spread to the AV node normally, but some activity will encounter the bypass tract and travel through this route.

Signals will be appropriately delayed at the AV node but NOT at the bypass tract, so the P wave is immediately followed by the QRS.

The bypass tract depolarizes slowly, however, so the QRS complex is wide.

Question 22

Drugs that serve as ___-channel blockers might cause a widened QRS complex. Why?

Answer 22

Na-channel blockers

This slows the phase 0 of cardiac myocytes, because phase 0 relies on these channels for rapid depolarization.

Blocking Na channels thus slows QRS.

Question 23

Examples of Na-channel blockers:

Answer 23

Class I anti-arrhythmics (e.g. flecainide)

Tricyclic antidepressant (e.g. amitriptylline)

Question 24

Potential causes of a small QRS complex:

Answer 24

Dampening effect of fluid, air, fat between heart and electrodes (e.g. pericardial or pleural effusion, obesity, emphysema, or pneumothorax)

Loss of viable myocardium (e.g. end-stage ischemic or non-ischemic heart failure)

Diffuse infiltration or myxoedematous involvement aka protein infiltration (amyloidosis, hypothyroidism)

Question 25

What voltage defines a small QRS complex?

Answer 25

Amplitude of all QRS complexes in limb leads are <5 mm

Amplitude of QRS in precordial leads are <10mm

Question 26

______ abnormalities can cause abnormalities in repolarization.

Answer 26

Electrolyte abnormalities can cause abnormalities in repolarization.

Question 27

Electrolyte abnormalities can cause abnormalities in _____.

Answer 27

Electrolyte abnormalities can cause abnormalities in repolarization.

Question 28

The potassium current is responsible for phase(s) ____.

Answer 28

2/3 - repolarization

Question 29

Hyperkalemia ____ the slope of phase 2/3.

Question 30

Overall consequences of hyperkalemia:

Answer 30

K current is responsible for phase 2/3, so hyperkalemia increases the slope of phase 2/3 causing peaked T waves and shortened QT intervals.

Makes the resting membrane potential less negative which inactivates Na channels - widens the QRS and prolongs the PR, causes loss of ST segment, “sinusoidal” QRS/QT, and prone to VT/VF.

Question 31

What is indicated by this EKG?

Answer 31

Late hyperkalemia

Question 32

Hypokalemia ___ the slope of phase 2/3, which delays _____.

Answer 32

Hypokalemia decreases the slope of phase 2/3, which delays ventricular repolarization.

Question 33

EKG findings of Hypokalemia:

Answer 33

T wave flattening and inversion

ST depression

Prominant U waves

Apparent long QT interval due to fusion of T and U

(Prone to arrhythmias)

Question 34

The calcium currents are responsible for phase(s) ____ in cardiac myocyte APs.

Answer 34

Phase 2/3

Question 35

Hypercalcemia _____(speeds/slows) repolarization.

Answer 35

SPEEDS

Question 36

EKG findings of hypercalcemia:

Answer 36

Short QT interval (due to short ST segment)

Osborne wave

Question 37

Hypocalcemia ____(speeds/slows) repolarization.

Answer 37

SLOWS

Question 38

EKG findings of hypocalcemia:

Answer 38

Long QT interval (due to long ST segment)

Question 39

What electrolyte abnormality is responsible for each tracing?

Answer 39

Question 40

What is a normal QTc value?

Answer 40

<440 in men

<460 in women

(QTc = QT/sqrtRR)

Question 41

Most common types of Long QT Syndrome:

Answer 41

Loss of function mutation of I_ks

Loss of function mutation of I_kr

Gain of function mutation of I_Na

Question 42

What drugs are commonly associated with long QT?

Answer 42

Antipsychotics - e.g. haldoperidol, quetiapine, olanzapine

Antiarrhythmics - e.g. quinidine, procainamide, sotalol, amiodarone

Antidepressants - e.g. amitriptyline, citalopram

Antihistamines - e.g. diphenhydramine, loratidine

Antibiotics - e.g. macrolides, fluoroquinolones