Chapter 13: Cardiac Arrhythmias And ECG Interpretation

Question 1

What are the main causes of cardiac arrhythmias ?

Answer 1

1) Abnormal rhythmicity of the pace maker.
2) Shift of the pacemaker from the sinus node to another place of the heart
3) Blocks at different places in the spread of the impulse through the heart.
4) abnormal pathways of impulse transmission through the heart.
5) Spontaneous generation of spurious impulses in almost any part of the heart.

Question 2

What is the ratio of HR increase/ increase in each degree of body temperature in Celsius?

Answer 2

18 beats/ 1 degree Celsius

Question 3

How does fever cause tachycardia?

Answer 3

It increases the metabolic rate of the sinus node, which in turn increases the rate of sinus nodal pacing.

Question 4

How does Severe blood lose increase the heart rate ?

Answer 4

Severe blood loss activates sympathetic reflex stimulation of the heart which may increase the HR to a range between 150-180 BPM.

Question 5

How does simple myocardial plegia cause tachycardia?

Answer 5

A week myocardium will not be able to pump blood into the Arterial tree normally. Which will cause reduction in BP and will cause tachycardia

Question 6

Mechanism of bradycardia in athletic heart?

Answer 6

The large ventricular volume and myocardial contractility allows the athletic heart to pump to increase resting stroke volume than the normal heart. This increased blood in the Arterial tree will activate feedback circulatory reflexes or other effects that cause bradycardia.

Question 7

Pathophysiology of carotid sinus syndrome ?

Answer 7

It is caused by the excessive sensitivity of the baroreceptors of the carotid sinus walls. Mild pressure on the baroreceptors of the carotid sinus causes intense vagal acetylcholine effect on the heart leading to bradycardia and sometimes syncope.

Question 8

Physiology of respiratory sinus arrhythmia?

Answer 8

Respiratory sinus arrhythmia results from the spillover of signals from the medullary respiratory center into the adjacent vasomotor center during inspiratory and respiratory cycles of respiration. This spillover causes alternate increase in the number of sympathetic and parasympathetic impulses passed on to the heart, which in ECG is manifested as RSA

Question 9

Blood supply of the AV node ?

Answer 9

In 90% of humans AV node receive it’s blood supply from the AV nodal branch of RCA. In 10% of the people it is left circumflex artery.

Question 10

Blood supply of the bundle of Hiss?

Answer 10

It has dual blood supply from the AV nodal branch of the RCA and the first septal branch of the LAD artery.

Question 11

Blood supply of the SA node?

Answer 11

In 60% it is the SA nodal branch of the RCA in the remaining 40% it can be from the LCA or Left coronary circumflex artery.

Question 12

Blood supply of the right atrium and ventricle?

Answer 12

The RCA branches supply both of them.

Question 13

Blood supply of the left atrium?

Answer 13

Left coronary circumflex artery, it also supplies the posterio-lateral wall of the left ventricle

Question 14

Blood supply of the left ventricle?

Answer 14

The anterior and anterio- lateral walls are supplied by the LAD artery

Question 15

Blood supply of the interventricular septum?

Answer 15

The anterior 2/3 is supplied by the anterior interventricular branch of the septal branch of the left coronary artery. The posterior 1/3 is supplied by the posterior interventricular branch of the RCA

Question 16

What are the key etiologies of AV blocks ?

Answer 16

1) AV nodal ischemia
2) AV nodal compression by the scar tissue
3) Inflammation of the AV node
4) extreme vagal stimulation

Question 17

What is the maximum pathological time prolongation PR interval can have ?

Answer 17

0.35 to 0.45 seconds by then the AV nodal conduction will stop entirely

Question 18

The higher the prolongation of PR interval the severe the acute rheumatic heart disease. True/ False?

Answer 18

True

Question 19

What are the causes of premature contractions?

Answer 19

1) Local area of ischemia
2) small calcified plaques at different parts of the heart that irritate the myocardium
3) toxic irritation of the AV node, purkinje system or myocardium by toxins, infection, drugs, nicotine, caffeine etc.
4) PAC is also frequent in cardiac catheterization.

Question 20

Premature atrial contraction?

Answer 20

PACs are caused by ectopic foci in the atrium, it is usually followed by a prolongation of succeeding PR interval which is called compensatory pause.

Question 21

What is the cause of compensatory pause in PAC?

Answer 21

The premature excitation of the sinus node by the current from the ectopic focus will cause a delay in spontaneous depolarization of the sinus node which is manifested as the compensatory pause in ECG.

Question 22

Cause of PAC ?

Answer 22

It often occurs in healthy athletes, it can also occur due to mild toxic conditions like smoking, alcohol, too much coffee etc.

Question 23

ECG pattern of PVC ?

Answer 23

1) considerably prolonged QRS Complex
2) The QRS Complex has high voltage due to lateralized depolarization of one ventricle ahead of the other.
3) After all PVC QRS the T wave has an exactly opposite Polarity as the preceding QRS. It is because the cardiac muscle fibers that are depolarized first also repolarize first.

Question 24

What are the types of PVCs considered dangerous?

Answer 24

The PVCs results from stray impulse or reentry phenomenon originating around the borders of ischemic or infarcted portions of the heart because they can persipitate lethal ventricular fibrillations.

Question 25

What causes Long QT syndrome?

Answer 25

Disorders that delay repolarization of the ventricles.

Question 26

What is the risk of long QT syndrome?

Answer 26

It increases a patient’s susceptibility to develop a ventricular arrhythmia called Toesades de pointes. Which means twisting of the points.

Question 27

ECG pattern of Toesades induced by LQT syndrome?

Answer 27

The QRS Complex may change over time. With the onset of arrhythmia usually following a premature beat- a pause- and another beat with prolongation of QT interval + arrhythmia/ tachycardia/ ventricular fibrillation.

Question 28

What are the etiologies of Long QT syndrome?

Answer 28

Congenital disorders of mutations of sodium or potassium channel genes.
Acquired Long QT syndrome are more common and are associated with hypomagnesemia, hypocalcemia, hypokalemia, excessive antiarrhythmic drugs such as quinidine or antibiotics like fluoroquinolones or erythromycin.

Question 29

Clinical symptoms of long QT syndrome?

Answer 29

It can be precipitated by physical exercise, intense emotions like fright or anger or being startled by noise.

Question 30

What is the management of acute long QT syndrome?

Answer 30

Magnesium sulfate

Question 31

What is the management of chronic long QT syndrome?

Answer 31

Beta blockers or surgical implantation of cardiac defibrillator.

Question 32

Paroxysmal tachicardia mechanism?

Answer 32

It is tachicardia occur in paroxysm that starts abruptly and ends abruptly. It is hypothesized to be caused by re-entrant circus movement feedback pathways that set up local repeated self re excitation around irritable foci

Question 33

How to stop paroxysmal atrial tachycardia?

Answer 33

By eliciting vagal inhibition through carotid sinus massage or deep exhilation or antiarrhythmic drugs

Question 34

ECG of ventricular tachycardia?

Answer 34

It is marked by paroxysm of ventricular tachicardia with wide QRS+ inverted T wave.

Question 35

Why is Ventricular tachycardia dangerous?

Answer 35

It occurs either due to considerable ischemic damage of the ventricles or due to cardiac irritation caused by the heart failure drug digitalis. VT can precipitate V fib.

Question 36

What is the treatment of VTach ?

Answer 36

Lidocaine - it can decrease the permiability of sodium thereby blocking the activation of irritable foci.
Amiodarone- It can prolonged AP and refractory period in cardiac muscle and slowing AV conduction.
Electrical Cardioversion

Question 37

What are the fundamental mechanisms of ventricular fibrillation?

Answer 37

When the circus movement of re-entry circuit reaches its point of origin when that point is in refractory state of excitation, the circle will complete and there will be no berserk circuit occuring. However, if the pathway around the circle is much longer than normal as in enlarged ventricles or the velocity of conduction is sufficiently slow or the refractory period is significantly shortened , it can cause berserk circus movements of impulses.

Question 38

What is the most common cause of the long circular pathway for V fib electrical circuit?

Answer 38

Enlargement of the ventricles

Question 39

What are the conditions that cause reduction in the velocity of the circus movement current in fibrillation?

Answer 39

Purkinje system blocks, ischemia of the muscles, hyperkalemia etc