1. Einthoven\'s Triangle - A.) Explain the differences between the “P-wave” vector with the “R-wave” vector based on the electrical and anatomical properties of the heart. B.) Often the “R-wave” vector with the “T-wave” vector have similar directions and magnitudes. Explain why that might be. Solution Ans: 1. The QRS complex is made up of three waves. These waves indicate the changing direction of the electrical stimulus as it possess through the heart’s conduction system. The largest wave in the QRS comples is the R wave. The R wave represent the electrical stimulus as it possess through main portion of the ventricular walls. The walls of the ventricles are very thick due to the amount of work they have to do and consequently, more voltage is required. This is why the R wave is by far the biggest wave generated during normal condition.as against T wave vector. P-wave : The P-wave represents spread of electrical activity through the atrial musculature after the sino-atrial node discharges. In man the P-wave begins about 0.02 second before the atrial contraction. Variations in direction of migration of the electrical disturbance may produce variations in configuration of the P-wave. One of the practical problems in electrocardiology is identification of the P-waves. Identification may be difficult when the P-wave is iso-electric, or when rapid heart rates cause the P-wave to be superimposed on the T-wave. 2. Postpacing precordial T-wave inversion (TWI), known as cardiac memory (CM), mimics ischemic precordial TWI, and there are no established ECG criteria that adequately distinguish between the two. On the basis of CM properties (postpacing sinus rhythm T vector approaching the direction of the paced R vector). The CM induced by right ventricular pacing would manifest a TWI pattern different from that of precordial ischemic TWI, thereby discriminating between the two. On the basis of the key attribute of CM (T-wave vector in sinus rhythm approaching the direction of the abnormally activated QRS complex), The right ventricular endocardial pacing would result in a precordial TWI with frontal-plane T-vector direction different from that of ischemic precordial TWI. Although precordial TWI was originally described with proximal LAD lesions, ischemia in the territory of the left circumflex (LCx) and occasionally right coronary artery (RCA) can also cause precordial TWI. T-Wave: Passage of the QRS disturbance through the ventricle is presumed to leave the ventricle in a disturbed state both electrically and metabolically. Reconstitution of the resting electrical state of ventricles develops while the ventricular muscle is still contracting and the dipoles developed during the electrical reconstitution or recovery in the ventricle give rise to the T-wave. A negative wave is sometimes seen following the P-wave and represents the recovery disturbance or to T-wave of the atrium. The recovery disturbance is labeled Ta. Ordinarily Ta is buried in the QRS c.