SA Medical - General Medicine And Imaging of Disease

Stimulation of the pacemaker of the heart causes tachycardia. Tachycardia >100 bpm Increased body temperature Sympathetic stimulation of the heart - 150 to 180 bpm Toxic conditions - digitalis toxicity Vagal stimulation of the heart causes a decrease in heart rate.   Bradycardia <60 bpm. Parasympathetic system - acetylcholine. Carotid sinus syndrome - an atherosclerotic process causes excessive sensitivity of the baroreceptors in the atrial wall. External pressure to the neck causes the atherosclerotic plaque in the carotid sinus to stimulate the baroreceptors, which then stimulate the vagus nerve and cause bradycardia. Abnormal cardiac Rhythms that result from impulse conduction block.  Rarely - Sinoatrial block - P waves are obsured by the QRS complex, and the ventricles pick up the rhythm originating from the atrioventricular node AV node AV block inhibits or completely blocks impulses originating in the SA node.  Ischemia of the AV node or AV bundle Compression

Remember the waves precede the contraction. The PR interval has a normal value of 0.16 seconds and is the delay between the atrial contraction and the beginning of the ventricular contraction. The QT interval has a normal value of 0.35 seconds - the time of ventricular contraction. The heart rate can be determined by the reciprocal of the time interval between each heart beat. During depolarisation process, the average electrical current flows from the base of the heart toward the apex. ECG leads - there are three bipolar limb leads. Lead I: negative lead is connected to the Right arm and the positive terminal is connected to the left arm. Lead II: the negative terminal of the ECG is connected to the right arm and the positive terminal is connected to the left leg. Lead III: the negative terminal is connected to the left arm and the positive terminal is connected to the left leg. Einthoven's Law states that the electrical potential of any limb lead equals the sum of the