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Twelve-Lead Electrocardiography - part 4

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các tâm thất được kích hoạt, nhưng bởi vì các gói còn lại là bị chặn, vách ngăn được kích hoạt bởi các sợi Purkinje từ bó bên phải, tạo ra một vector từ phải sang trái qua vách ngăn. Do đó, sự lệch đầu tiên của QRS của chúng tôi sẽ được tiêu cực dẫn V1 và tích cực trong động cơ V6 dẫn. | 46 Chpater 7 Intraventricular Conduction Delays The BBBs the ventricles to be activated but because the left bundle is blocked the septum is now activated by Purkinje fibers from the right bundle producing a right-to-left vector across the septum. Thus the first deflection of our QRS will be negative in lead V1 and positive in lead V6. Our normal initial R in lead V1 becomes a Q and our normal initial Q in lead V6 becomes an R. Next the right ventricle is activated but usually does not produce an R wave in V1 possibly for two reasons. The first is that the vector of right ventricular depolarization traveling from endocardium to epicardium toward lead V1 is partially counterbalanced by the continuing right-to-left vector in the opposite direction through the septum with its greater muscle mass. The second explanation is that upon normal activation of the right ventricle a large slow vector immediately begins to spread into the larger mass of the left ventricle across muscle from right to left also helping to counterbalance what would usually be our normal small R wave in lead V1. Nevertheless it is worthwhile to note that occasionally the right ventricular forces spreading from endocardium to epicardium are still strong enough in LBBB to produce a tiny R wave in leads V1 and V2 Figure 7.6 . Finally the right ventricle finishes depolarizing before the slow wave of depolarization has finished spreading from right to left across the left ventricle. This leaves the vector spreading through the left ventricle unopposed and completes the wide deep QS that we see in lead V1 in LBBB. Figure 7.6. Left bundle branch block with small R waves in V1 and V2. BBBs ST Segments and T Waves 47 While producing a deep QS in lead V1 these same right-to-left forces are producing a wide positive deflection in leads V5 and V6. Usually the QRS in the left precordial leads V5 and V6 is monophasic as seen in Figure 7.7 meaning that it goes in only one direction in this case upwardly without a