Transcript Slide 1
Disease of Cardiac System prepared by : Asaad Torkman & Mohammad Mosa Electrocardiogram (EKG, ECG) Definition : It is electrical activity generated by the heart can be measured by an array of electrodes placed on the body surface. For standard 12-leads ECG, 10 electrodes (six on the chest and four on the limbs) are placed on the body. The 12 Lead ECG Each of the 12 leads represents a particular orientation in space, as indicated next paragraph. (RA = right arm, LA = left arm, LF = left foot). Leads divided to three types. 1- Bipolar limb leads . 2- Augmented unipolar limb leads. 3- Unipolar (+) chest leads. Bipolar limb leads (frontal plane): Lead I: RA (-) to LA (+) (Right Left, or lateral) Lead II: RA (-) to LF (+) (Superior Inferior) Lead III: LA (-) to LF (+) (Superior Inferior) Augmented unipolar limb leads (frontal plane): Lead aVR: RA (+) to [LA & LF] (-) (Rightward) Lead aVL: LA (+) to [RA & LF] (-) (Leftward) Lead aVF: LF (+) to [RA & LA] (-) (Inferior) Leads I,II and VL look at the left lateral surface of the heart. Leads III and VF look at the inferior surface of the heart. Lead VR looks at the right atrium. Unipolar (+) chest leads (horizontal plane) Leads V1, V2, V3: (Posterior Anterior) Leads V4, V5, V6:(Right Left, or lateral) Leads V1 and V2 look at the right ventricles. Leads V3 and V4 look at the septum between the ventricles and the anterior wall of the left ventricle. Leads V5 and V6 look at the anterior and lateral walls of the left ventricle. THE CARDIAC AXIS cardiac axis the average directions of spread of the depolarization wave through the ventricles as seen from the front. Leads VR and II look at the heart from opposite directions. Seen from the front , the depolarization wave normally spreads through the ventricles from 11 o’clock to 5 o’clock ,so the deflections in lead VR are normally mainly downward (negative) and in lead II mainly upward (positive). The Shape of the ECG : P- wave: Depolarization of the right and left atria. QRS complex: Depolarization right and left ventricular. ST-T wave: Ventricular repolarization. U wave: Origin for this wave is not clear - but probably represents "after depolarisations" in the ventricles. PR interval: Time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex). The normal PRI is ,12- ,20 seconds. QRS duration: Duration of ventricular muscle depolarization. QRS is normally <,12 seconds. QT interval: Duration of ventricular depolarization and repolarization. RR interval: Duration of ventricular cardiac cycle (an indicator of ventricular rate). PP interval: Duration of atrial cycle (an indicator of atrial rate) Heart rate calculation Count the number of large squares between 2 consecutive R waves and divide into 300 OR memorize this scale 1 large squares = 300 bpm 2 large squares =150 bpm 3 large squares =100 bpm . Normal Sinus Rhythm Normal sinus rhythm occurs when the electrical impulse starts at a regular rate and rhythm in the sinus node and travels through the normal conduction pathway. Normal Sinus Rhythm The rules for this rhythm : REGURALITY : The R-R intervals are constant ; the rhythm is regular. RATE : The atrial and ventricular rates are equal ; heart rate is between 60 and 100 beats per minute. P WAVE : The P waves are uniform . There is one P wave in front of every QRS complex . Normal sinus rhythm PRI : the PR interval measures between 0.12 and 0.20 seconds ; the PRI measurement is constant across the strip. QRS : the QRS complex measures less than 0.12 seconds Sinus node Dysrhythmias Dysrhythmias are disorders of the formation or conduction (or both) of the electrical impulse within the heart. Types of sinus dysrhythmias : 1-SINUS BRADYCARDIA: The rate less 60bpm. Sinus Bradycardia associated with athletic training fainting attacks, hypothermia and myxoedema heart attack. Sinus Bradycardia The rules for this rhythm: REGULARITY: The R-R intervals are constants the RATE: The atrial and ventricular rates are equal; heart rhythm is regular. rate is less than 60 beats per minute. Sinus Bradycardia P-WAVE: There is a uniform P wave in front of every QRS complex. PRI: the PR interval measures between .12 and .20 seconds; The PRI measurement is constant across the strip. QRS: The QRS complex measures less than .12 seconds. 2-Sinus Tachycardia Sinus Tachycardia: The rate above 100bpm. Sinus tachycardia is associated with exercise, fear, pain, hemorrhage and thyrotoxicosis. SINUS TACHYCARDIA The rules for this rhythm : REGULARITY : The R-R intervals are constant; the rhythm is regular . RATE : The atrial and ventricular rates are equal ; the heart rate is usually 150 -250 beats per minute QRS : the QRS complex measures less than 0.12 seconds . SINUS TACHYCARDIA P WAVE : there is one P wave in front of every QRS complex . The configuration of the P wave will be different than that of sinus P wave ; they may be flattened or notched . Because of the rapid rate , the P waves can be hidden in the T waves of the preceding beats. PRI : the PRI is between 0.12 and 0.20 seconds and constant across the strip . The PRI may be difficult to measure if the P wave is obscured by the T wave . 3-Sinus Arrhythmia Similar to normal sinus rhythm except that PP and RR intervals are irregular because the SA node discharges at a variable frequency Atrial Dysrhythmias 1-Premature Atrial complex (PAC): The rules for this rhythm: REGULARITY: Since this is a single premature ectopic beat , it will interrupt the regularity of the underlying rhythm . RATE: The overall heart rate will depend on the rate of the underlying rhythm . Atrial Dysrhythmias P -WAVE: The P wave of the premature beat will have a different morphology than the P waves of the rest of the strip . It may be hidden within the T wave of the preceding complex. PRI: The PRI should measure between .12 and .20 seconds , but can be prolonged ; the PRI of the ectopic will probably be different from the PRI measurements of the other complexes . QRS: The QRS complex measurement will be less than0 .12 seconds. 2-Atrial fibrillation This is a result of many sites within the atria firing electrical impulses in an irregular fashion causing irregular heart rhythm. The rules for this rhythm: RATE: The atrial rate cannot be measured because its so chronic ; research indicates that it exceeds 350 beats per minute. P-WAVE: In this arrhythmia the atria are not depolarizing in an effective way ;instead ,they are fibrillating . Thus , no P wave is produced . 2-Atrial fibrillation PRI: Since no P waves are visible , no PRI can be measured . REGULARITY: The atrial rhythm is immeasurable; all atrial activity is chaotic . The ventricular rhythm is grossly irregular, having no pattern to its irregularity . QRS: The QRS complex measurements should be less than .12 seconds. 3-Atrial Flutter Atrial Flutter: In this abnormal rapid heart rhythm the abnormal tissue generating the rapid heart rate is also in the atria, however, the atrioventricular node is not involved. The rules for this rhythm : REGULARITY : the atrial rhythm is regular .The ventricular rhythm will be regular if the AV node conducts impulses through in consistent pattern . If the pattern varies , the ventricular rate will be irregular. 3-Atrial Flutter P WAVE : When the atria flutter they produce a series of well-defined P waves . When seen together , these “ flutter “ waves have a saw tooth appearance. RATE : Atrial rate is between 250 and 350 beats per minute . PRI: Because of the unusual configuration of the P wave ( flutter wave ) and the proximity of the wave to the QRS complex, it is often impossible to determine a PRI in this arrhythmia . Therefore , the PRI is not measured in atrial flutter . QRS : The QRS complex measures less than 0.12 seconds.