ECG

22 Questions

What is the primary function of the ECG machine?

To amplify the potentials detected on the surface of the body

What is the main difference between a Computer/Portable ECG and an Ambulatory ECG (Holter monitor)?

Computer/Portable ECG records a short period, while Ambulatory ECG records continuously for 24-72 hours

What is the purpose of an Event monitor?

To record only 1 or 2 leads when the patient triggers it during clinical signs

What term is used to describe the movement of the waveform away from the baseline in either a positive or negative direction?

Waveform

What term is used to describe the line between waveforms?

Segment

What term is used to describe the normal cardiac rhythm where depolarization begins at the SA node?

Sinus rhythm

What is the term used to describe an abnormal heart rhythm?

Arrhythmia

What is the term used to describe an increase in heart rate?

Tachycardia

What is the term used to describe a decrease in heart rate?

Bradycardia

What does the vertical axis in an ECG represent?

Amplitude in millivolts

What does a wider complex on the ECG indicate?

Fibrosis

What does the P wave represent in an ECG tracing?

Discharge of the SA node

How is left atrial and ventricular enlargement denoted on an ECG?

Wide and notched P wave

In small animals, at what paper speed is ECG conventionally recorded?

50 mm/sec

What determines if the paper speed for ECG can be 25 mm/sec in small animals?

Heart rate below 120 beats/min

What is the sum of all the electrical currents generated by the heart called?

Cardiac vector

What is the direction of the cardiac vector perpendicular to?

The border between depolarized and repolarized areas

What is the purpose of the Einthoven's triangle?

To view the heart from different angles

What does depolarization refer to in the context of cardiac electrophysiology?

The shift in the electrical charge from negative to positive

What follows depolarization during an action potential in excitable cells?

Repolarization

What determines when the next action potential can occur in cells?

Refractory period duration

How are changes in the amplitude, frequency, or shape of signals described in electrophysiology?

'Deflections'

Study Notes

ECG Terminology

Heart Rate: number of heartbeats per minute
Waveform: movement away from the baseline in either a positive or negative direction
Segment: a line between waveforms
Interval: a waveform and a segment
Complex: several waveforms
Tachycardia: increase in heart rate
Bradycardia: decrease in heart rate
Sinus Rhythm: normal cardiac rhythm where depolarization begins at the SA node
Arrhythmia: abnormal heart rhythm

How ECG Works

When cardiac impulses pass through the heart, the electrical current spreads into adjacent tissues
Electrodes can record the APs (action potentials)
A dipole (positive and negative charge separated by a small distance) can generate local current flow and a small electrical field
Standard calibration paper speed is 25 mm/sec in humans, 50 mm/sec in small animals
The horizontal axis represents time in milliseconds
The vertical axis represents amplitude in millivolts

ECG Components

Each component of an ECG tracing reflects an electrical event occurring in a specific part of the heart
The sequence of electrical events follows specific anatomic pathways within the heart
In health, these events are precise and consistent
ECG evaluation includes determination of heart rate, heart rhythm, and waveform morphology (amplitude and duration)

ECG Waves and Intervals

P Wave: represents depolarization of atrial muscle
QRS Complex: represents ventricular depolarization
T Wave: represents ventricular repolarization
PR Interval: represents the time between P wave and QRS complex
QT Interval: represents the time between QRS complex and T wave

ECG Leads

Einthoven's Triangle: electrodes are placed in the 2 arms (RA, LA) and 1 leg (LL)
Lead I: records voltage between LA and RA
Lead II: records voltage between LL and RA
Lead III: records voltage between LL and LA
Standard bipolar leads (I, II, and III) provide information on the frontal plane of the heart

ECG Types

In-hospital ECG: computer, portable, Alivecor Vet monitor, KardiaMobile
Ambulatory ECG (Holter monitor): records continuously for 24, 48, or 72 hours on multiple leads simultaneously
Event monitors: external event monitor and implantable event monitor (implanted subcutaneously)
Veterinarian Dr. Vieira's lecture goals:
- Know the major indications for an ECG
- Understand ECG terminology
- List the ECG waves and describe their significance
- List the most important segments/intervals and their significance

ECG History

Willem Einthoven introduced the term "electrocardiogram" in 1893
Einthoven proposed the placement of electrodes for ECG recording, which is now known as Einthoven's Triangle

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ECG