Understanding EKGs - Ch 3

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EKG Tech Exam

What is cardiac dysrhythmia?

Any abnormality in the rate, regularity or sequence of cardiac activation.

What are the two myocardial cell groups?

Myocardial cell groups: 1. The myocardial working cells 2. The specialized pacemaker cells of the electrical conduction system

What are myocardial working cells?

Responsible for generating the physical contraction of the heart muscle.

What are the functions of myocardial working cells?

1. contraction 2. relaxation

What are the walls of the atria and ventricles constructed of?

Myocardial working cells

How is a myocardial contraction produced?

When the permeated contractile filaments of the myocardial working cells are electrically stimulated, a contraction is produced.

What generates blood flow?

The physical contraction of myocardial tissue

What is required to produce the physical contraction in a heart?

Organized electrical activity

What happens to the size of the atria and ventricles when the myocardial tissue contracts and blood is ejected from the chambers?

The size of the atria and ventrical decreases

How are the myocardial working cells and specialized pacemaker cells different?

The specialized pacemaker cells DO NOT contain contractile filaments & DO NOT have the ability to contract.

What are the specialized pacemaker cells (aka specialized group) responsible for?

Controlling the rate & rhythm of the heart by coordinating regular depolarization.

Where are the specialized group cells found?

In the electrical conduction system of the heart.

What are the primary functions of the specialized myocardial pacemaker cells?

The generation and conduction of electrical impulses

Cardiac muscle cells have the ability to contract in response to which stimuli? (Hint: 4)

1.Thermal 2.Chemical 3.Electrical 4.Mechanical

Atrial muscles contract ____________.

simultaneously

Ventrical muscles contract ___________.

together

What does threshold refer to in heart anatomy?

The point at which a stimulus will produce a response.

Why does cardiac muscle function on an all-or-none principle?

When a stimulus is strong enough for a cardiac cell to reach the threshold, ALL the cells will respond and will contract. If no stimulus, none of the cardiac muscles will contract.

What is high sodium (Na) blood levels?

Hypernatremia

What is low sodium (Na) blood levels?

Hyponatremia

What are the four primary characteristics of cardiac cells?

1. Automaticity 2. Excitability (irritability) 3. Conductivity 4. Contractility (rhythmicity)

Which characteristic of cardiac cells is automatic and mechanical?

Contractility

Pertaining to cardiac cells, what are the electrical functions of the heart?

1.Automaticity 2.Excitability 3.Conductivity

What is the ability of the cardiac pacemaker cells to generate their own electrical impulses spontaneously without external (or nervous) stimulation?

Automaticity

What intrinsic spontaneous depolarization frequency produces contraction of myocardial muscle cells?

Automaticity

What characteristic is specific to the pacemaker cell sites of the electrical conduction system (i.e., the SA node, AV junction, and the Purkinje network fibers)?

Automaticity

What is the ability of cardiac cells to respond to an electrical stimulus?

Excitability (or irritability)

What characteristic is SHARED by all cardiac cells?

Excitability and Conductivity

A weaker ____________ can cause a contraction when a cardiac cell is highly irritabile.

stimulus

What is the ability of cardiac cells to receive an electrical stimulus and then transmit it to other cardiac cells?

Conductivity

What characteristic of cardiac cells form synctium, because they function collectively as a unit?

Conductivity

When there is more than one unit, what is the correct term to describe synctium?

Syncytia

What is the ability of cardiac cells to shorten and cause cardiac muscle contraction in response to an electrical stimulus?

Contractility

What is the coordination of cardiac muscle cells to produce a regular heartbeat?

Contractility

What is the mechanical function of the heart?

Contractility

Why are both mechanical and electrical cardiac function influenced by electrolyte imbalances?

Because myocardial cells are bathed in electrolyte solutions.

What is an electrolyte?

An electrolyte is a substance (compound) whose molecules dissociate into charged components (ions) when placed in water.

What happens when electrolytes are placed in water?

Positive or negative charged ions are produced.

What is an ion with a positive (+)charge?

cation (pronounced kation)

What is an ion with a negative (-) charge?

anion (pronounced aneon)

What are the THREE major cations that affect cardiac function?

1.Potassium (K) 2.Sodium (Na) 3.Calcium (Ca)

What is the fourth cation?

4.Magnesium (Mg)

What are the three intracellular (inside the cell) cations?

1.Potassium (K) 2.Magnesium (Mg) 3.Calcium (Ca)

What is the extracellular (outside the cell)cation?

Sodium (Na)

How does K (Potassium) affect major cardiac function?

Potassium performs a major function in cardiac depolarization and repolarization.

What is an increase in potassium blood levels?

Hyperkalemia

What is a decrease in potassium blood levels?

Hypokalemia

What role does Sodium (Na) play in cardiac function?

Na (Sodium) plays a vital part in depolarization of the myocardium.

An increase in sodium blood levels is known as:

Hypernatremia

A decrease in sodium blood levels is known as:

Hyponatremia

What role does Calcium (Ca) play in cardica muscle?

Causes an important function in myocardial depolarization and myocardial contraction.

What is an increase in calcium blood levels?

Hypercalcemia

What is a decrease in calcium blood levels?

Hypocalcemia

When the cardiac cells are at rest, what is happening to the Potassium (K) and Sodium (Na)ions?

In their resting state, K is greater on the inside and Sodium is greater on the outside of the cardiac cell.

Which ions diffuse through the membrane more readily? (Hint: Potassium or Sodium)

Potassium

What is the sodium-potassium exchange pump?

Potassium and Sodium ions are moved in and out of the cell through the cell membrane.

What is the charge of the inside of a cardiac cell during the polarized or resting state?

Negative

What is recorded on the EKG strip during the resting period?

A baseline or isoelectric line

What happens to the sodium at the end of cardiac depolarization?

Actively returns to the outside of the cell and potassium returns to the inside of the cell.

How does the sodium and potassium exchange occur?

This exchange takes place via the sodium-potassium exchange pump.

What happens to the cardiac cell when they have returned to the recovered, or repolarized state?

The cardiac cell is now read to be stimulated again.

Which is slower, repolarization or depolarization?

Repolarization

Which is faster, depolarization or repolarization?

Depolarization

What is the LAST area to be depolarized in a healthy cardiac muscle?

The first area to be repolarized

Cardiac muscle tissue has a __________________ to ensure that the muscle is totally relaxed before another action potential or depolarization can be initiated.

refractory period

What is the refractory period of atrial muscle?

Approximately .15 seconds

What is the refactory period of the ventricle muscle?

Approximately .25 - .3 seconds

Which rate of contractions are potentially faster, ventricles or atria?

Atria

When do the cardiac cells have a brief resting period?

After electrical impulse stimulation and myocardial contraction

What is this brief resting period of the cardiac cells?

Cardiac repolarization

During the repolarization period, what two stages does the heart go through?

1. Absolute refractory period 2. Relative refractory period

During most of the process of repolarization, the cardiac cell: (Hint: 2 responses)

1. Is unable to respond to a new electrical stimulus.2. Cannot spontaneously depolarize

What is the state of an activity in which the cardiac cell cannot spontaneously depolarize?

Absolute Refractory Period

What is the period when repolarization is almost complete & the cardiac cell can be stimulated to contract prematurely if the stimulus to contract prematurely if the stiumulus is much stronger than normal?

Relative refractory period

What is the second part of the refractory period that follows the absolute refractory period?

Relative refractory period

Where is the relative refractory period shown on the EKG strip?

The downslope of the T wave

What is another name for the relative refractory period?

Vulnerable period of the cardiac cells

Where is the absolute refractory period on the EKG strip?

The beginning of the QRS complex to the peak of the T wave

The primary function of the myocardial working cells include:

Contraction and relaxation

The ability of cardiac pacemaker cells to generate their own electrical impulses spontaneously without external, or nervous, stimulation is known as:

Automaticity

Which characteristic is specific to the pacemaker sites of the electrical conduction system (i.e., the SA node, the AV junction, and the Purkinje network fibers)?

Automaticity

The ability of cardiac cells to respond to an electrical stimulus is referred to as:

Excitability

Excitability is also referred to as:

Irritability

The ability of cardiac cells to receive an electrical stimulus and then transmit the stimulus to other cardiac cells is known as:

Conductivity

What characteristic shared by all cardiac cells?

Conductivity

Cardiac muscle cell groups that function collectively as a unit are known as:

Syncytia

Which is a slower process, repolarization or depolarization?

Repolarization

The period when repolarization is almost complete and the cardiac cell can be stimulated to contract prematurely if the stimulus is stronger than normal is known as:

Relative refractory period

Cardiac depolarization may be thought of as the period during which __________ ions rush into the cell.

Sodium

At the end of cardiac depolarization, __________ ions return to the inside of the cell.

Potassium

The resting state of a cardiac cell, wherein the inside of the cell is electrically negative relative to the the outside of the cell, is called:

Polarized state

The point at which a stimulus will produce a cell response is called the:

Threshold

An increase in potassium blood levels is known as:

Hyperkalemia

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