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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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Parts of an ECG
An electrocardiogram - an ECG - or the dutch and german version of the word - elektrokardiogram or EKG, is a tool used to visualize “gram” the electricity “electro” that flows through the heart “cardio”.
An ECG tracing specifically shows how the depolarization wave moves during each heartbeat - which is a wave of positive charge - looks from the perspective of different sets of electrodes.
This particular set of electrodes is called lead II, with one electrode on the right arm and the other on the left leg, so essentially when the wave’s moving toward the left leg electrode, you get a positive deflection, like this big positive deflection correspond to the wave moving down the septum.
To read an ECG there are a few key elements to keep in mind, one of them includes figuring out the rate and rhythm. There are a couple ways of figuring out the heart rate on an ECG.
The first one is called the “box method” because you count the number of boxes between heartbeats. Each small box represents 0.04 seconds, and each big box is five small boxes, so each big box is 0.2 seconds.
To do that, you can count the number of small boxes between R waves since R waves are tall and pointy and easy to see in lead 2 of an ECG strip.
You can find an R wave that has a peak that falls at the beginning of a box, and then count up how many boxes until the same point on the next R wave.
Let’s say that there are 4 big boxes and 1.5 small boxes between two R waves, meaning there are 4 x 5 + 1.5 = 21.5 small boxes, and that means there’s 0.04 seconds x 21.5 or .86 seconds between heartbeats.
Now, to get something a little more meaningful we can take the inverse which is 1 over 0.86 beats per second, or 1.16 beats per second.
Now there’re 60 seconds in a minute, so multiplying that by 60 we end up with 70 beats per minute—the heart rate!
Now, if the distance between two R waves is exactly 1 big box, then the heart rate would be 300 beats per minute—really fast. If R waves are two big boxes apart or 0.4 seconds apart, then the heart rate is 150 beats per minute.
Three big boxes apart is 100 beats per minute, four, five, and six big boxes apart is 75, 60, and 50 beats per minute respectively.
Remembering these numbers makes it easier to make a rough estimate. For example, if there are three to four large boxes between R waves, then the heart rate must be between 75 and 100 beats per minute.
Another method to determine the heart rate is to count the number of beats in ten seconds, which is the standard length of time on the rhythm strip portion of a 12-lead ECG.
The heart is a muscle that regularly beats to pump blood throughout the body. An electrocardiogram (ECG) is a test that records the electrical activity of the heart, which shows how fast and strong the heartbeats are.
The heart rate refers to the number of contractions of the heart per minute. This one can vary according to an individual's age, but usually, the normal heart rate for adults falls between 60 and 100 beats per minute. The rhythm refers to the pattern of electrical impulses that cause the heartbeat. The normal cardiac rhythm is a regular sinus rhythm, which means that each heartbeat follows a predictable pattern. There may be abnormal rhythms, such as atrial fibrillation and ventricular fibrillation, both serious and life-threatening conditions.
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