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Cardiovascular system anatomy and physiology
Lymphatic system anatomy and physiology
Abnormal heart sounds
Normal heart sounds
Changes in pressure-volume loops
Cardiac and vascular function curves
Altering cardiac and vascular function curves
Law of Laplace
Measuring cardiac output (Fick principle)
Stroke volume, ejection fraction, and cardiac output
Physiological changes during exercise
Cardiovascular changes during hemorrhage
Cardiovascular changes during postural change
Cardiac conduction velocity
Electrical conduction in the heart
ECG normal sinus rhythm
ECG QRS transition
ECG rate and rhythm
ECG cardiac infarction and ischemia
ECG cardiac hypertrophy and enlargement
Control of blood flow circulation
Microcirculation and Starling forces
Blood pressure, blood flow, and resistance
Compliance of blood vessels
Laminar flow and Reynolds number
Pressures in the cardiovascular system
Resistance to blood flow
Action potentials in myocytes
Action potentials in pacemaker cells
Cardiac excitation-contraction coupling
Excitability and refractory periods
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An electrocardiogram is also known as an ECG; the Dutch and German version of the word, elektrokardiogram, is shortened to EKG. It is a tool used to visualize, or “gram,” the electricity, or “electro,” that flows through the heart, or “cardio.” Specifically, an ECG tracing shows how the depolarization wave, which is a wave of positive charge, moves during each heartbeat by providing the perspectives of different sets of electrodes. This particular set of electrodes is called lead II; one electrode is placed on the right arm and the other on the left leg. Essentially, when the wave’s moving toward the left leg electrode, you get a positive deflection. This big, positive deflection corresponds to the wave moving down the septum. To read an ECG, there are a few key elements to keep in mind; one is to figure out the QRS transition.
The chest leads will have a mostly positive deflection, if a depolarization wave is moving towards them. The QRS transition zone refers to where the QRS complex switches from being mostly negative to mostly positive, from the point of view of the chest leads, V1 through V6, which “view” the heart through the horizontal plane. The QRS transition usually happens in lead V3 or V4, depending on factors such as chest lead placement and the exact anatomy of a person’s heart. So, the QRS transition tells us when the overall QRS vector is aligned in the direction of the chest leads; it’s a way of understanding what’s happening to the QRS axis in the horizontal plane.
The QRS transition in an ECG is the point at which the QRS complex changes from positive to negative or vice versa. This change reflects the depolarization of the ventricles, and is caused by the flow of current from the atria through to the ventricles. The QRS transition occurs when the ventricles reach their depolarization peak and is therefore a good measure of how well-paced the heartbeat is.
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