HEART PHYSIOLOGY(ARRYTHMIAS)BY

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

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).

Premature Contractions

Definition: A premature contraction is a contraction of the heart before the time that normal contraction would have been expected.

Synonyms: extrasystole, premature beat, or ectopic beat.

Depending upon the site of ectopic impulse, we divide the extrasystoles into three types i.e.

1. Atrial extrasystole

2. Junctional/AV nodal extrasystole

3. Ventricular extrasystole

Causes of Premature Contractions:

(1)Local areas of ischemia

(2) small calcified plaques at different points in the heart, which press against the adjacent cardiac muscle so that some of the fibers are irritated;

(3) toxic irritation of the A-V node, Purkinje system, or myocardium caused by drugs, nicotine, or caffeine.

(4) cardiac catheterization

Premature Atrial Contractions

ectopic origin of the beat is in the atria near the A-V node

The P wave of this beat occurred too soon in the heart cycle; the P-R interval is shortened.

compensatory pause: the interval between the premature contraction and the next succeeding contraction is slightly prolonged, which is called a compensatory pause

Pulsus Deficit: difference b/w the heart rate and radial pulse rate.

Premature atrial contractions occur frequently in otherwise healthy people.

Indeed, they often occur in athletes whose hearts are in very healthy condition.

CAUSE: Mild toxic conditions resulting from such factors as smoking, lack of sleep, ingestion of too much coffee, alcoholism, and use of various drugs can also initiate such contractions.

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A-V Nodal or A-V Bundle (junctional) Premature Contractions

The P wave is missing from the ECG.

the P wave is superimposed onto the QRS-T complex

A-V nodal premature contractions have the same significance and causes as atrial premature contractions.

Premature Ventricular Contractions (PVC’s)

1. The QRS complex is usually considerably prolonged.

2. The QRS complex has a high voltage

3. After almost all PVCs, the T wave has an electrical potential polarity exactly opposite to that of the QRS complex i.e. T wave is inverted.

Premature Ventricular Contractions (PVC’s)

Causes of PVCs: Some PVCs are relatively benign in their effects on overall

pumping by the heart; they can result from such factors as cigarettes, coffee, lack of sleep, various mild toxic states, and even emotional irritability.

Conversely, many other PVCs result from signals that originate around the borders of infarcted or ischemic areas of the heart.

Risk of PVCs: may lead to V. fibrillation.

PAROXYSMAL TACHYCARDIA

Definition: there is paroxysms of tachycardia, they appear suddenly and may remain for sometime.

Paroxysmal means a series of rapid heart beats suddenly start and then suddenly stop.

Types: Supraventricular tachycardias (SVTs)

ATRIAL

AV NODAL

Ventricular tachycardias

Atrial Paroxysmal Tachycardia

• An ectopic focus in the atria start discharging at a rate of 100 – 150 impulses.

• Heart follows these depolarizations.

• ECG Findings: P wave is inverted and is partially superimposed on the T wave of previous heartbeat.

Can be stopped with: vagal reflex e.g carotid massage or

occulocaridac reflex

Antiarrythmic drugs: quinidine or procainimide

AV NODAL/ JUNCTIONAL TACHYCARDIA

• an ectopic focus in AV node or junctional tissue discharges impulses at a rate of 100 -150 /minute. Heart follows these discharges.

• There is no P wave, just only QRS complexes at a fast rate.

• Supra ventricular tachycardias (SVTs) can be controlled by vagal stimulation done by carotid massage or by occulocaridac reflex. (when firm pressure is applied over the eye ball there is slowing of heart rate. Afferent pathway for occulocardiac reflex is along the trigeminal nerve, then from the vasomotor centre impulses are sent to heart rate.

Ventricular Paroxysmal Tachycardia It’s a serious condition and it indicates considerable myocardial damage.

• Digitalis (digoxin) may also cause it.

In many cases V. tachycardia results into ventricular fibrillation.

Factors which lead this tachycardia into ventricular fibrillation are:

shortened refractory period of ventricular muscle

longer pathway that the impulse has to travel

slow velocity of conduction of cardiac impulse

Treatment: Quinidine increases refractory period of cardiac muscle and can eliminate the problem