3.2.1. Arrythmias

Question 1

What is a Normal Sinus Rhythm?

Answer 1

Normal Sinus Rhythm - a heart rate between 60-100 bpm; originating in the sinus node and normally conducted to the ventricle (with the normal PR interval)

Question 2

What is an arrhythmia? What causes it?

Answer 2

Arrhythmia - any cardiac rhythm that is not normal sinus rhythm; causes a fall in cardiac outputs; results from alterations of impulse conduction, impulse formation, or both

Question 3

Tachycardia vs Bradycardia?

Answer 3

TACHYCARDIA: ventricular rate > 100 bpm BRADYCARDIA: ventricular rate < 60 bpm

Question 4

What is overdrive suppression?

Answer 4

Overdrive Suppression: when the subsidiary pacemaker cells are inactivated due to the net hyperpolarization seen when the SA node is active

Question 5

What is a subsidiary pacemaker? Conditions required for this?

Answer 5

Subsidiary Pacemaker: cells of the AV node and purkinje fibers of the ventricles that also have spontaneously depolarizing phase 4 AP’s; these cells kick in should the sinus node fail Increased concentration of Na+ required

Question 6

What is Decremental conduction? What does it result in?

Answer 6

Decremental Conduction: slower conduction or even a conduction block; caused by the pre-mature RE-stimulation of the AV node which results in less calcium influx, delaying subsequent conductions. Faster stimulation rates = slower conduction due to reduced Ca2+ channel availability

Question 7

What is reentry?

Answer 7

Reentry: self-perpetuating waves of depolarization; results in tachycardia

Question 8

3 things required for reentry besides a good first date (zing)

Answer 8

presence of adjacent cardiac tissues with different refractory periods unidirectional conduction block slow conduction to allow refractory tissue to recover and allow conduction where it was previously blocked

Question 9

What is anatomic reentry?

Answer 9

Anatomic reentry: obstacle around which reentry occurs is anatomic (i.e. tricuspid annulus or a scar); typically has a regular rate and unchanging, monotonous EKG pattern due to the stable nature of the circuit.

Question 10

What is functional reentry? Where do we usually see this?

Answer 10

Functional Reentry: obstacle is a moving area of temporary block resulting from diffuse abnormalities in the tissue. Usually seen in severely damaged atria or ventricles with large areas of ischemia.

Question 11

Two treatments for recurrent tachycardia/reentry

Answer 11

1. 360 Joules of defibrillation 2. electrical countershock depolarizes the entire myocardium, blocking the recurrent wavefront

Question 12

What is circus movement and what does it require?

Answer 12

Circus Movement: another name for recurrent tachycardias (reentry), due to their “circular and self-regenerating” pattern. This phenomenon is dependant upon the presence of heterogeneities between adjacent portions of the heart that allow for simultaneous block and conduction

Question 13

What are AV-Blocks?

Answer 13

A-V Block: inhibition of atrial conduction; causes an increase in the PR length of EKG

Question 14

What is a first degree AV Block? EKG findings? Symptoms of this?

Answer 14

First-Degree AV block: Conduction between atria and ventricles is delayed due to an abnormal AV node. Prolonged PR interval with each P wave followed by a QRS complex. Asymptomatic.

Question 15

What are the types of second degree AV block?

Answer 15

Mobitz Type I (Wenckebach) Mobitz Type II (Hay)

Question 16

Describe Mobitz Type I (Wenckebach) second degree AV block. What EKG findings are associated with it? What symptoms do we see with this?

Answer 16

Intermittent failure of AV conduction. Progressive lengthening of the PR interval until a beat is “dropped” (P wave not followed by a QRS complex). Usually asymptomatic and rarely progressive to third-degree AV block

Question 17

Describe Mobitz Type II (Hay) second degree AV block. What EKG findings are associated with it and what progress does it make?

Answer 17

Sudden, unpredictable loss of AV conduction. Dropped beats (QRS intervals) not preceded by a change in the length of PR intervals. It is often described as the ratio of P waves to QRS complexes, with a 2:1 block most commonly seen. Often progresses to third-degree AV block and may require prophylactic pacing

Question 18

What is third degree AV block? Discuss the EKG pattern and treatment.

Answer 18

Failure of any impulses to be conducted from atria to ventricles. Atria and ventricles beat independently of each other (AV dissociation), in which ventricles are depolarized by AV nodal or ventricular escape rhythm. As a result, both P waves and QRS complexes are present, but there is no relationship between P waves and QRS complexes. Atrial rate is faster than ventricular rate; usually treated with a pacemaker.

Question 19

What is Wolff-Parkinson-White syndrome and what does it cause electrically?

Answer 19

congenital abnormality where a muscle remnant makes an electrical connection between the atrium and the ventricle; this results in pre-mature excitation of the ventricle through a non-decrementally conducting pathway, changing the pattern of the QRS (has a characteristic delta wave on ECG); May result in a reentry current, leading to supraventricular tachycardia.

Question 20

4 requirements for Wolff-Parkinson White

Answer 20

1. Short P-R interval (< 120 ms) 2. Normal P wave vector (to exclude junctional rhythm) 3. Presence of a delta wave, slurring or notching of the first portion of the QRS complex 4. QRS duration greater than 100 ms

Question 21

What is a Bundle Branch Block (BBB)?

Answer 21

Bundle Branch Block: When a bundle branch or fascicle becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately.

Question 22

What does a BBB do to the electrical pathway?

Answer 22

This results in altered pathways for ventricular depolarization. Since the electrical impulse can no longer use the preferred pathway across the bundle branch, it may move instead through muscle fibers in a way that both slows the electrical movement and changes the directional propagation of the impulses.

Question 23

Effect of BBB on the heart’s activity?

Answer 23

As a result, there is a loss of ventricular synchrony, ventricular depolarization is prolonged, and there may be a corresponding drop in cardiac output. (The affected ventricle depolarizes much more slowly)

Question 24

What does an atrial flutter do and why?

Answer 24

Atrial Flutter: causes an anatomic reentry (macroreentry) due to the tricuspid annulus presenting as the obstacle

Question 25

What in exact terms is an Atrial flutter and what does the EKG look like?

Answer 25

Regular, rapid (250-350/min) arrhythmia originating from the atria. ECG shows a rapid succession of identical, back-to-back atrial depolarization waves, giving a “sawtooth” appearance. Not all atrial impulses are transmitted to ventricles because the AV node is in refractory period.

Question 26

Electrical result of an atrial fibrillation

Answer 26

Atrial fibrillation - irregularly irregular, rapid (350-600/min) impulses from multiple atrial foci depolarize the atria. Chaotic and erratic baseline with no discrete P waves and irregularly spaced QRS complexes.

Question 27

Anatomical result of atrial fibrillation

Answer 27

Associated with right and left atrial enlargement. Atrial contraction is ineffective, causing decreased cardiac output and atrial stasis, and therefore predisposes for emboli formation and subsequent stroke.

Question 28

Treatment for atrial fibrillation

Answer 28

warfarin

Question 29

Electrical pattern for ventricular fibrillation

Answer 29

rapid, irregular ventricular depolarization due to impulses that originate from multiple ectopic ventricular foci. Completely erratic rhythm with no identifiable waves.

Question 30

Treatment for ventricular fibrillation

Answer 30

Fatal arrhythmia without immediate defibrillation.

Question 31

Describe how cell injury, resulting in a less negative resting potential, alters ionic events in depolarization and repolarization.

Answer 31

Will result in different speeds of conduction, which may lead to fibrillation and possible tachycardia or bradycardia (usually more negative and less negative respectively)

Question 32

What type of AV block is this? How do you know?

Answer 32

Mobitz 1: progressive lengthening of the PR interval until a beat is “dropped” (more P waves than QRS waves)

Question 33

What type of AV block is this? How do you know?

Answer 33

First: prolonged PR interval seen

Question 34

What type of AV block is this? How do you know?

Answer 34

Third Degree: complete heart block, atrial rate is greater than the ventricular, no relationship between the two chambers. PR constantly changing without altering ventricular rhythm.

Question 35

What type of AV block is this? How do you know?

Answer 35

Mobitz 2: dropped beats that are not preceded by a change in the length of the PR interval; usually seen as 2:1 block, meaning that there are 2 or more P waves for every QRS response. May see increased QRS length (indicative of total heart disease