conduction disorders- Heart Blocks

Question 1

What are the types of Heart blocks?

Answer 1

1. AV Blocks

2. Bundle branch blocks

Question 2

What is the aetiology of AV blocks?

Answer 2

-Physiological: ↑ vagal tone
-Pathophysiological:
Idiopathic fibrosis of the conduction system
Ischemic heart disease
Cardiomyopathy (e.g., due to amyloidosis or sarcoidosis)
Infections (e.g., Lyme disease, bacterial endocarditis)
Hyperkalemia (> 6.3 mEq/L)
-Iatrogenic
Side effect of certain drugs (e.g.,beta blockers, calcium channel blockers, digitalis)
Cardiac interventions (e.g., surgery, alcohol septal ablation)

Question 3

what are the types of AV blocks?

Answer 3

1st degree
2nd degree: mobitz type 1 (wenkeback) and mobitz type 2
3rd degree: complete block

Question 4

what is first degree AV block?

Answer 4

1. def:
   PR interval > 200 ms
   No interruption in atrial to ventricular conduction
   Rate of SA node = heart rate
2. Characteristics:
   May be found in healthy individuals, e.g., in athletes with ↑ vagal tone
   Usually asymptomatic
   Often discovered incidentally on ECG.
3. Treatment:
   Clinical assessment for underlying diseases (e.g., structural heart diseases, electrolyte imbalances)
   Usually no specific treatment necessary
   Follow-ups to evaluate progression of the disease
   Pacemaker
   If the patient also exhibits wide QRS complexes on ECG → identify the level of AV block (within or below the bundle of His) using intracardiac electrogram → if conduction time from the bundle of His to the ventricles is > 100 ms: pacemaker placement
   Symptomatic patients: unpleasant awareness of the heartbeat due to loss of atrioventricular synchrony (pacemaker syndrome)

Question 5

what is second degree AV Block- Mobitz Type 1/Wenckeback?

Answer 5

Usually asymptomatic
May present with symptoms of reduced cardiac output, resulting in hypoperfusion (e.g., dizziness, syncope) and bradycardia
Irregular pulse
Treatment
Asymptomatic patients
Clinical assessment for underlying diseases (e.g., structural heart diseases, electrolyte imbalances)
Usually no specific treatment necessary
Follow-ups (ECG and cardiac monitoring) to evaluate progression of the disease
Symptomatic patients
Hemodynamically stable
Monitoring with transcutaneous pacing pads
If symptoms not reversible → placement of a permanent pacemaker
Hemodynamically unstable
Atropine
Temporary cardiac pacing (if not responsive to atropine)
Emergency management of bradycardia

Question 6

what is mobitz type 2 second degree block?

Answer 6

-Definition:
Single or intermittent non-conducted P waves without QRS complexes
The PR interval remains constant.
The conduction of atrial impulses to the ventricles follows regular patterns:
2:1 block: regular AV block that inhibits conduction of every other atrial depolarization (P wave) to the ventricles (heart rate = ½ SA node rate)
3:1 block: regular AV block with 3 atrial depolarizations but only 1 atrial impulse that reach the ventricles (heart rate = ⅓ SA node rate)
3:2 block: regular AV block with 3 atrial depolarizations but only 2 atrial impulses that reach the ventricles (heart rate = ⅔ SA node rate)
-Second-degree atrioventricular blocks
Symptoms/clinical findings
Bradycardia → ↓ cardiac output
Fatigue
Dyspnea
Chest pain
Dizziness, syncope
-Treatment
Hemodynamically stable patients:
Monitoring with transcutaneous pacing pads
Clinical assessment for underlying diseases (e.g., structural heart diseases, electrolyte imbalances)
If symptoms are not reversible → placement of a permanent pacemaker
Hemodynamically unstable patients:
Atropine
Temporary cardiac pacing
Emergency management of bradycardia
The second-degree AV block Mobitz type II may progress to a third-degree block and is an unstable condition that requires monitoring and treatment!

Question 7

what is 3rd degree AV block?

Answer 7

1.Definition
Third-degree AV block is a complete block with no conduction between the atria and ventricles.
AV dissociation: on ECG, P waves and QRS complexes have their own regular rhythm but bear no relationship to each other
A ventricular escape mechanism is generated by sites that are usually located near the AV node or near the bundle of His.
The more distant the site of impulse generation:
The slower the ventricular escape mechanism
The wider and more deformed the QRS complex
Block proximal to bundle of His: narrow QRS complexes
Block distal to bundle of His: wide QRS complexes
The worse the prognosis
Sudden onset of a third-degree AV block results in asystole, which lasts until the ventricular escape mechanism takes over. This asystole may lead to Stokes-Adams attacks.
Third-degree AV blockThird-degree atrioventricular block and ventricular escape rhythm

2. Symptoms/clinical findings
Symptoms depend on:
Rate of ventricular escape mechanism
Bradycardia (< 40 bpm) with cerebral hypoperfusion (fatigue, irritability, apathy, dizziness, syncope, cognitive impairment), heart failure, dyspnea
Length of asystole 
Nausea, dizziness
Stokes-Adams attacks 
Cardiac arrest

3. Treatment
   Hemodynamically stable patients:
   Monitoring with transcutaneous pacing pads
   Clinical assessment for underlying diseases (e.g., structural heart diseases, electrolyte imbalances)
   No reversible causes → placement of a permanent pacemaker
   Hemodynamically unstable patients:
   Atropine
   Temporary transcutaneous or transvenous cardiac pacing
   In the event of low blood pressure, administer dopamine.
   In the event of heart failure, administer dobutamine.

Question 8

what do you do in cardiac arrest?

Answer 8

1.UNRESPONSIVE ?
2.SHOUT FOR HELP
3.OPEN AIRWAY
4.NOT BREATHING
NORMALLY ?
5.CALL EMERGENCY NUMBER
(999 IN UK)
6. 30 CHEST
COMPRESSIONS
2 RESCUE BREATHS
30 COMPRESSIONS
7.If the ECG shows a shockable rhythm – ventricular fibrillation or pulseless ventricular tachycardia then an unsynchronized shock of 150–200 J biphasic (360 J monophasic) is
delivered without delay via paddles or self-adhesive pads
followed immediately by 2 minutes of CPR. For a nonshockable rhythm – asystole or pulseless electrical activity, 2 minutes of CPR is delivered with 1 mg of intravenous
adrenaline (epinephrine)

Question 9

what are the causes of sudden cardiac arrest?

Answer 9

Cardiac arrhythmias (e.g. ventricular fibrillation)
Sudden pump failure (e.g. acute myocardial infarction)
Acute circulatory obstruction (e.g. pulmonary embolism)
Cardiovascular rupture (e.g. aortic dissection, myocardial
rupture)
Vasomotor collapse (e.g. in pulmonary hypertension)

There are two mechanisms of sudden unexpected cardiac
arrest:
 Ventricular fibrillation or pulseless ventricular tachycardia
(VF/VT)
 Non-VF/VT (asystole and pulseless electrical activity also
known as electromechanical dissociation)

Question 10

how is VF/VT treated?

Answer 10

Ventricular fibrillation or pulseless ventricular tachycardia
is readily treated with IMMEDIATE defibrillation,
cardiopulmonary resuscitation (CPR) and drugs.
Intravenous amiodarone is the first-line drug in refractory
VF/pulseless VT. When treating VF/VT cardiac arrest,
adrenaline 1 mg is given after the third shock and then
every 3–5 min. Amiodarone 300 mg is also given after
the third shock, particularly if VT/ VF have recurred after
defibrillation.
One paddle is placed to the right of the upper sternum
and the other over the cardiac apex

Question 11

how is non VT/asystole treated?

Answer 11

Asystole is more difficult to treat but the heart may
respond to atropine. However atropine is not longer
recommended for routine use. More recently,
vasopressin has been shown to be successful. If there
is any sign of slow electromechanical activity (e.g.
bradycardia with a weak pulse), emergency pacing
should be used. Continued CPR is critical and drug
management is rarely effective.
 Pulseless electrical activity: several potentially reversible
causes are listed in the universal algorithm (Fig. 14.32).
It carries a very poor prognosis. Effective treatment
involves co

Question 12

what is the difference between cardioversion and DEfic?

Answer 12

When the arrhythmia has definite QRS complexes, the
delivery of the shock should be timed to occur with
the downstroke of the QRS complex (synchronization)
(Fig. 14.33). The machine being used to perform the cardioversion will do this automatically if the appropriate button is
pressed. There is a crucial difference between defibrillation
and cardioversion: a non-synchronized shock is used to defibrillate.

Question 13

what is cardioversion used for?

Answer 13

Typical indications for DCC include:
 Atrial fibrillation
 Atrial flutter
 Sustained ventricular tachycardia
 Junctional tachyarrhythmias.
If atrial fibrillation or flutter has been present for >48 hours,
it is necessary to anticoagulate the patient adequately for
3 weeks before elective cardioversion to reduce the risk of
embolization. Alternatively, cardioversion may be performed
if intra-atrial thrombus is ruled out using a transoesophageal echo,

Question 14

What is temporary pacing used for?

Answer 14

Bradycardia due to slow intrinsic heart rate or AV block
2 types:
Transvenous and transcutaneous
Permanent is used for complete heart block

Question 15

what is intra aortic balloon pumping used for?

Answer 15

1. Acute heart failure. Balloon pumping is used to
   improve cardiac output when there is a transient or
   reversible depression of left ventricular function, such as in a patient with severe mitral valve regurgitation who is awaiting surgical replacement of the mitral valve, or in a patient with a ventricular septal defect that is due to septal infarction. It may also be used to support patients awaiting heart transplantation.
2. Unstable angina pectoris. Balloon pumping is used to treat unstable angina pectoris by improving coronary
   flow and decreasing myocardial oxygen consumption
   by reducing the ‘afterload’. This technique may be
   successful, even when medical therapy has failed. It is
   followed by early angiography and appropriate definitive therapy such as surgery or coronary angioplasty