Heart Block and ECG

ELECTROCARDIOGRAPHY AND HEART BLOCK
• DR. Parijat Biswas

Fig A : AP in ventricular muscle
Depolarisation
Einthovens triangle and law
• The sum of the voltage in
lead I and III is equal to the
voltage in lead II at any
instant of cardiac cycle.
Lead I + lead III = lead II
Arrhythmia
Arrhythmia
• An arrhythmia describes an irregular

heartbeat or an abnormality in cardiac
rhythm. With this condition, a person’s heart
may beat too quickly, too slowly, too early,
or with an irregular rhythm
Types of Arrhythmias
• Abnormal sinus rhythm
tachycardia
Bradycardia
sinus arrhythmia
• Abnormal rhythm due to impulse
conducting block ( heart block)
• Some Common types of cardiac arrhythmias:
• Atrial fibrillation
• Atrial flutter
• Supraventricular tachycardia
• Ventricular tachycardia
• Ventricular fibrillation
• Heart block
Heart Block
Definition
• Interference with the generation and
conduction of cardiac impulses by variety
of arrhythmias and ECG changes is called
heart block.
Heart block is categorise as:
• Sinoatrial block
the impulse from sinus node is blocked before it enter the
atrial muscle. In ECG :sudden cessation of P wave. The
ventricle picks up a new rhythm.
• Atrioventricular block
Types of atrioventricular (AV) Block
• 1st Degree
• 2nd Degree
• 3rd Degree
1st + 2nd degree= incomplete heart block
3rd degree= complete heart block
Causes of atrioventricular (AV) Block
• Ischemia of AV node
• Compression of AV bundle by scar tissue
• Inflammation of AV node or bundle
• Extreme stimulation of heart by Vagus

Causes of 3 rd degree heart block
• Congenital heart diseases
• MI
• Rheumatic fever
• Infective endocarditis
• Cardiomyopathy
• Calcification of the bundle of His

Ventricular escape
• When Rhythmical excitatory signal fails to transmit into
ventricle, the ventricle stop beating for 5 to 20 sec, after that
purkinje fiber develop a rhythm of it’s own and causes
ventricular contraction at a rate of 15 to 40 beats per min. this
phenomenon is called ventricular escape.

Stokes-Adams syndrome
• When A-V block occurs— the cardiac impulse fails to pass from the atria into
the ventricles through the A-V nodal and bundle system— then a new
pacemaker usually develops in the Purkinje system at a new rate somewhere
between 15 and 40 beats per minute. After sudden A-V bundle block, the
Purkinje system does not begin to emit its intrinsic rhythmical impulses until 5 to
20 seconds later. During these 5 to 20 seconds, the ventricles fail to pump blood,
and the person faints during this first 4 to 5 seconds because of lack of blood
flow to the brain. This delayed pickup of the heartbeat is called Stokes-Adams
syndrome. If the delay period is too long, it can lead to death.
Circulatory readjustment during exercise
Circulatory readjustment during
exercise
• Three major e ect occur during exercise that are essential for
circulatory system to supply the tremendous blood flow
required by muscle.
• 1. Increase sympathetic discharge throughout the body

• 2.Increase arterial pressure
• 3. Increase cardiac output
Mass sympathetic discharge
• At the onset of exercise, higher level of the brain stimulates
vasomotor center to initiate mass sympathetic discharge , which
causes:
• Increased heart rate
• Increased stroke volume
• Arterioles of the peripheral circulation are strongly contracted EXCEPT

the arterioles of active muscle
• Capacitance vessels (Vein) are contracted powerfully, which increases

MSFP in turn venous return.
Increase Arterial pressure
Blood Pressure (BP) = CO(cardiac output) x TPR (total peripheral resistance)
= (SV x HR) x TPR
• 1. Vesoconstriction of the arterioles except the active

muscle. Increase TPR
• 2.Increase pumping activity of the heart. Increase stroke

volume
• 3. Increase venous return.

Increases Cardiac Output
• It increases 2.5 fold during exercise commonly .it can be
achived 4-7 fold in marathon runner.
• During exercise mean systemic filling pressure increases

which increases venous return . This results partly from
sympathetic stimulation of the capacitance vessels and
partly from visceral compression.
Increases blood flow in active muscle
during exercise
• The blood flow to the skeletal muscle during exercise can be
increases more then 20 fold . From 1litter/min to as great as
20 L / min.
• During rest blood flow skeletal muscle average 3to 4 ml/
min/ 100gm of muscle. During extreme exercise the rate can
be increases as much as 15 to 25 fold.
• Local regulation
• Vesodilation due to accumulation of metabolites and lack of oxygen
• Nervous control
Thank You

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ELECTROCARDIOGRAPHY AND HEART BLOCK

• DR. Parijat Biswas

• An arrhythmia describes an irregular

• Compression of AV bundle by scar tissue

• Inﬂammation of AV node or bundle

• Extreme stimulation of heart by Vagus

• Calciﬁcation of the bundle of His

• When Rhythmical excitatory signal fails to transmit into

ventricle, the ventricle stop beating for 5 to 20 sec, after that

purkinje ﬁber develop a rhythm of it’s own and causes

ventricular contraction at a rate of 15 to 40 beats per min. this

phenomenon is called ventricular escape.

• 1. Increase sympathetic discharge throughout the body

• Increased heart rate

• Increased stroke volume

• Arterioles of the peripheral circulation are strongly contracted EXCEPT

• Capacitance vessels (Vein) are contracted powerfully, which increases

• 1. Vesoconstriction of the arterioles except the active

• 2.Increase pumping activity of the heart. Increase stroke

• 3. Increase venous return.

• During exercise mean systemic ﬁlling pressure increases

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