General ECG/heart stuff

Question 1

Numbers for normal, tachycardia and bradycardia HR?

Answer 1

Normal: 60-100 bpm
Tachycardia: > 100 bpm
Bradycardia: < 60 bpm

Question 2

How do you calculate HR from an ECG? (if regular)

Answer 2

Count the number of large squares present within one R-R interval.
Divide 300 by this number to calculate heart rate.

Question 3

How do you calculate HR from an ECG? (if irregular)

Answer 3

Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long).
Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute).

Question 4

How would you know if there is sinus rhythm?

Answer 4

the p wave is present

Question 5

What is a normal PR interval?

Answer 5

120-200ms (3-5 small squares)
A prolonged PR interval suggests the presence of atrioventricular delay (AV block).

Question 6

What is first degree heart block?

Answer 6

First-degree heart block involves a fixed prolonged PR interval (>200 ms).

Question 7

What is second degree heart block type 1?

Answer 7

also known as Mobitz type 1 AV block or Wenckebach phenomenon

Progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped.

AV nodal conduction resumes with the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.

Question 8

What is second degree heart block type 2?

Answer 8

also known as Mobitz type 2 AV block

A consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.

Dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wave.

Question 9

What is third degree heart block?

Answer 9

occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction.

Typical ECG findings include the presence of P waves and QRS complexes that have no association with each other, due to the atria and ventricles functioning independently.

Question 10

What is a delta wave?

Answer 10

A slurred upstroke of the QRS complex.

PR interval can be shortened. This may be because the atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall. This is an accessory pathway and can be associated with a delta wave (associated with Wolff Parkinson White syndrome).

Question 11

ECG changes in Wolff-Parkinson-White syndrome

Answer 11

Short PR interval, less than 0.12 seconds
Wide QRS complex, greater than 0.12 seconds
Delta wave

Question 12

Treatment for Wolff-Parkinson-White syndrome?

Answer 12

radiofrequency ablation of the accessory pathway

Question 13

what should you not give to a patient with Wolff-Parkinson-White syndrome and who presents with atrial arrhythmias (e.g., atrial fibrillation or atrial flutter)? Why? What instead?

Answer 13

adenosine, verapamil or a beta blockers

They block the atrioventricular node, promoting conduction of the atrial rhythm through the accessory pathway into the ventricles, causing potentially life-threatening ventricular rhythms.

In this scenario, the usual management is procainamide (which does not block the AV node) or electrical cardioversion (if unstable).

Question 14

Narrow vs broad width of QRS complex?

Answer 14

less than 0.12 = narrow
more than 0.12 = broad

Question 15

What do tall QRS complexes imply?

Answer 15

Tall complexes imply ventricular hypertrophy (although can be due to body habitus e.g. tall slim people).

Question 16

What can delta waves be a sign of?

Answer 16

a sign that the ventricles are being activated earlier than normal from a point distant to the AV node. The early activation then spreads slowly across the myocardium causing the slurred upstroke of the QRS complex.

Question 17

What is considered a pathological Q wave?

Answer 17

A pathological Q wave is > 25% the size of the R wave that follows it or > 2mm in height and > 40ms in width.