1st Lecture on Arrythmias by Dr. ROOMI

HEART PHYSIOLOGY(ARRYTHMIAS)

BYDR. MUDASSAR ALI ROOMI (MBBS, M. PHIL)

Assistant Professor Physiology

ARRYTHMIAS• Definition of arrythmia: variation

from the normal rhythm of the heart beat, encompassing abnormalities of the rate, regularity, site of impulse origin and sequence of activation.

• There are two main types of arrythmias:

1. Normotropic arrythmias: when SA node is still the pacemaker of heart.

2. Ectopic arrythmias: when SA node is no more the pacemaker of heart.

ARRYTHMIAS

NORMOTROPIC ARRYTHMIAS• SINUS TACHYCARDIA• SINUS BRADYCARDIA• SINUS ARRYTHMIAS

ECTOPIC ARRYTHMIAS• HEART BLOCKS: SA nodal BLOCKS AV nodal BLOCKS(1st,2nd, 3rd

degree).• EXTRASYSTOLE ( atrial, AV nodal

and ventricular).• PAROXYSMAL TACHYCARDIA (

atrial, AV nodal, ventricular ).• OTHERS ( atrial flutter, atrial

fibrillation, ventricular fibrillation).

SINUS TACHYCARDIA• Normal heart rate (normocardia)

= 60-100 beats/min.• In this case heart rate is greater

than 100 beats/min • Causes:

– Exercise (physiological)– emotional states (physiological)– anxiety (physiological)– hyperthyroidism (pathological)– Epinephrine – Sympathetic stimulation

(physiological)– Atropine (anticholinergic drug)– Increased body temperature e.g.

fever (pathological)

• Calculate the heart rate by the formulae:

• HR = 1500 ss/no. of smallest squares between two successive R waves. (OR)

• HR= 300 big squares/ no. of big squares b/w two successive R waves.

SINUS TACHYCARDIA (cont..)• Effect of temperature on heart rate: With each degree Fahrenheit, heart rate

increases by 10 beat/min (18 beat/min for each degree Celsius) upto 105 F.• beyond 105 F, the heart rate may decrease because of progressive debility of the

heart muscle as a result of the fever. • MECHANISM: Fever causes tachycardia because increased temperature increases

the rate of metabolism of the sinus node, which in turn directly increases its excitability and rate of rhythm.

•increased temperature

•Increase in the rate of metabolism of the sinus node

•Increase in excitability

SINUS BRADYCARDIA• It means a slow heart rate usually

less than 60 beats /min.• Causes of sinus bradycardia:

– Bradycardia in athletes (physiological) ***

– Carotid sinus syndrome (pathological) – Vagal stimulation such as during

vomiting, – cholinergic drugs e.g. pilocarpine.– Hypothyroidism (pathological) – hypothermia, – severe depression, (pathological) – raised intracranial pressure

(pathological) – In some infections e.g. enteric fever

(typhoid fever) there is relative bradycardia.***

– Antiadrenergic (propranolol)

• Calculate the heart rate by the formula:

• HR = 1500/no. of smallest squares between two successive R waves.

SINUS BRADYCARDIA (cont..)• Bradycardia In athletes: • Cardiac output (C.O) = stroke

volume (S.V)* heart rate (H.R).

• In athletes, there is physiological hypertrophy of heart (forceful heart). stroke volume (SV) is permanently increased. So, at rest the cardiac output is maintained at 5.5 L/min by decreasing heart rate.

SINUS BRADYCARDIA (cont..)

• Carotid sinus syndrome: – In some individuals if we apply

slight pressure on carotid sinus, it causes bradycardia.

– It is due to arteriosclerosis or calcification of carotid sinus which increases the sensitivity of baroreceptors and thus causing bradycardia.

• When we perform carotid massage there is slowing of heart rate.

SINUS ARRHYTHMIA

• It is a physiological condition i.e. – heart rate increases during

inspiration and – decreases during expiration.

• This variation of heart rate becomes more marked during deep breathing.

• This variation can be recorded by cardiotachometer.

SINUS ARRHYTHMIA (cont..)

• Mechanism of sinus arrythmia: it involves three possible mechanisims:

1. There is spread of excitation from the inspiratory neurons to nearby vasomotor center to increase heart rate during inspiration.

2. Impulses from stretch receptors in the lungs go to vasomotor centre to increase heart rate when lungs expand during inspiration.

3. Bainbridge reflex: during inspiration there is more negative intrathoracic pressure, so venous return increases to the right atrium. Impulses originate from the low pressure stretch receptors in the wall of atria and large vessels and these impulses go along the sensory fibers in vagus nerve to vasomotor centre to increase heart rate during inspiration.