4th Lecture on Arrythmias by Dr. Roomi

HEART PHYSIOLOG PHYSIOLOGY Y (ARRYTHMIAS) BY DR. MUDASSAR ALI ROOMI (MBBS, M. PHIL) Assistant Professor Physiology

ATRIAL FLUTTER

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Atrial flutter is a condition caused by a circus movement movement in the atria. the electrical signal travels as a single large wave always in one direction around and around the atrial muscle mass. Atria beat regularly at a rate of 250 – 350 beats / minute. All impulses from atria are not conducted to ventricles because AV node and purkinje system system have longer refractory period.

ATRIAL FLUTTER (cont..)

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so every second or third impulse is conducted. So there is 2:1 or 3:1 rhythm and ventricular rate is 125 /min.

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in ECG we see saw tooth shaped P waves. waves.

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Atrial flutter responds to carotid massage.

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The radial pulse is regularly irregular. irregular. (MCQ)

ATRIAL FIBRILLATION •

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Atria beat irregularly at a rate of about 400 to 600/ minute. impulses from the atria are conducted to ventricles at irregular intervals. Cause: frequent cause of atrial fibrillation is atrial enlargement resulting from heart valve lesions e.g mitral stenosis. Mechanism:  –

re-entry movements, movements ,

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division of impulses.

ECG findings : P waves are replaced by small, irregular and low voltage records. QRS Complexes Complexes are normal but placed at unequal distances.

ATRIAL FIBRILLATION (cont..) •

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Ventricular rate is 125- 150 / minute. There is pulsus deficit because weak heart beats fail to be transmitted to radial artery Radial pulse: there is irregularly irregular radial pulse (MCQ).

In cases of A. Fib, There is ultimately heart failure because of the rapid heart rate; diastole becomes too short so there is inadequate filling, less stroke volume and less cardiac output. Also because of rapid heart rate, rest period for the heart decreases.

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the efficiency of ventricular pumping is decreased only 20 to 30 percent. Why??

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Treatment: Digoxin, electroshock treatment

Ventricular Fibrillation •

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it is a fatal condition. Patients who die from acute myocardial myocar dial infarction show this  just before before death. Ventricles contract in parts not as a whole, stroke volume decreases, venous return will dilate the heart. ECG findings: There are irregular bizarre waves in ECG. Question: ventricular fibrillation often occurs without atrial fibrillation. Likewise, fibrillation often occurs in the atria without ventricular fibrillation. Why????

MECHANISM OF FLUTTER AND FIBRILLATION •

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SINGLE OR MULTIPLE FOCI THEORY : there is a single or multiple foci which discharge impulses at very rapid rate. CIRCUS MOVEMENT THEORY : there is movement movement of impulses along the same s ame pathway again and again. And this results into circus movement. Causes of circus movements are: 1. 2. 3.

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long pathway Decr De crea ease sed d vel eloc ocit ity y of con ondu duct ctio ion n shortened re refractory pe period

Division of impulses or chain reaction may lead to fibrillation. Suppose in the heart there are refractory areas, which may be because of in part depolarization or may be because of infarcted areas. These areas don’t allow the cardiac

impulse to pass. When a single impulse reaches the refractory area so this single impulse divides into two to avoid the refractory area. And so on leading to fibrillation.

Cardiac Arrest •

A final serious abnormality of the cardiac rhythmicity-conduction system is cardiac arrest.

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This results from cessation of all electric electrical al control signals in the heart.

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That is, no spontaneous rhythm remains. remains.

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Cause: Cardiac arrest is especially likely to occur during deep anesthesia , when many patients develop severe hypoxia because of inadequate respiration. Prognosis (outcome):  –

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In most instances of cardiac arrest from anesthesia, prolonged cardiopulmonary cardiopulmonary resuscitation (many minutes or even hours) is quite successful in reestablishing a normal heart rhythm. In some patients, severe myocardial disease can cause permanent or semipermanent cardiac arrest, which can cause death. To treat the condition, rhythmical electrical impulses from an implanted electronic cardiac pacemaker have been used successfully to keep patients alive for months to years.