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CPR Week 1 > 3.1.4. Basis of the Surface ECG > Flashcards

3.1.4. Basis of the Surface ECG Flashcards

1
Q

What is neuronal input within the heart responsible for?

A

Modulating activity (electrical signal originates within the heart itself)

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2
Q

How many APs per contraction (heart beat)?

A

1

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3
Q

Why do APs take on different morphologies in different parts of the heart?

A

It is a reflection of the ion channel population in each cell and its function

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4
Q

Where does cardiac Ap originate?

A

Specialized cardiac myocytes that exhibit pacemaker activity (SA node)

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5
Q

What nerve is responsible for parasympathetic innervation and what does it do?

A

Vagus. Slows down HR via ACh

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6
Q

What nerve is responsible for sympathetic innervation and what does it do?

A

T1-4 Spinal Nerves. Speeds up HR via Norepinephrine

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7
Q

Why does excitation start in the SA node?

A

Because it is the fastest pacemaker
SA: 70-80 APs/min
AV: 40-60
Purkinje: 15-40

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8
Q

What is the significance of atrial contraction?

A

Provides a “kick” to fill the ventricle

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9
Q

What is the Frank-Starling mechanism?

A

Strength of contraction is proportional to the end diastolic volume/ pressure

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10
Q

How is AP conducted to the ventricle?

A

Slowly (allows complete emptying of atrial contents), through the AV node.

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11
Q

What is the most important difference b/w fast- and slow-response cardiac APs

A

The ion responsible for the phase 0 upstroke:

Fast-response AP = fast inward Na+ current
Slow-response AP = slow inward Ca current

This is why conduction is slow in the AV nodes, but fast in the His-Purkinje system

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12
Q

Which ventricle is excited first?

A

Both, simultaneously

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13
Q

Where is AP conducted from in terms of the heart’s anatomy?

A

Base to Apex, then back Basal after reaching the Ventricles

Endocardium to the Epicardium

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14
Q

How does repolarization occur?

A

Epicardium to Endocardium

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15
Q

In which layer of the heart is the AP the shortest?

A

Epicardium

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16
Q

The total time from impulse initiation in the SA node to

repolarization of the ventricles

A

600 msec

17
Q

What is an ECG?

A

An extracellular recording of the mean cardiac vector over time

18
Q

Does the ECG measure heart contraction?

A

No. Only electrical activity

19
Q

Which part of the body serves as the ground electrode?

A

Left leg

20
Q

Which leads provide frontal plane information?

A

Limb leads

21
Q

Which leads provide horizontal plane information?

A

Chest leads

22
Q

Why does the R wave increase in amplitude for chest leads?

A

Because the left ventricle is larger than the right

23
Q

What is the zone of transition?

A

The lead where R- and S-wave amplitudes are roughly the same

24
Q

Which ECG intervals and durations are important to look out when determining if the heart in functioning properly?

A

PR interval
QRS duration
ST segment
QT interval

25
Q

What does a shortened PR interval mean?

A

Wolfe-Parkinson-White Syndrome

Signals are entering from other areas than the AV node

26
Q

What does a widened QRS duration mean?

A

Slow conduction in Purkinje fibers and/pr ventricular muscles

27
Q

What is someone at greater risk for who has shortened or increased QT intervals?

A

Cardiac arrhythmias

28
Q

What does Bazett’s correction account for?

A

The heart’s affect on the AP duration

29
Q

What is the normal axis of the apex?

A

-30 to 90 degrees

30
Q

What does the ST segment reflect?

A

AP plateau (changes = ischemia)

31
Q

What happens when the heart becomes ischemic?

A

An ATP-sensitive K+ channel opens after sensing the metabolic distress. This causes the AP to shorten dramatically in ischemic cells.

32
Q

What is atrial flutter?

A

Back to back P waves; creates a sawtooth appearance on the ECG

33
Q

What will you see on the ECG of patients with hypokalemia or bradycardia?

A

a U-wave (small bump after the T wave)

34
Q

What can irregularly spaces QRS be a sign of?

A

Atrial fibrillation (no discernible P wave)

35
Q

Medications that can prolong QT

A

Sotalol, Risperidone (antipsychotics), Macrolides, Chloroquine, Protease Inhibitors, Quinidine, Thiazides

36
Q

Congenital long QT syndrome

A
  1. Inherited disorder of myocardial repolarization
  2. Romano-Ward Syndrome
  3. Jarvell and Lange-Nielsen Syndrome (deafness)
  4. Predisposes patients to Torsades de pointes (polymorphic ventricular tachycardia)
37
Q

What is ventricular fibrillation?

A

Completely erratic rhythm. It is fatal w/o immediate CPR and defibrillation

CPR Week 1 (14 decks)

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