An action potential has several phases; hypopolarization, depolarization, overshoot, repolarization and hyperpolarization. Hypopolarization is the initial increase of the membrane potential to the value of the threshold potential.

A substance that decreases membrane permeability to sodium would likely decrease the probability of generating an impulse.

The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement. In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell.

How does an action potential differ prom simple depolarization? A depolarization is any change in a neuron that makes it more positive than resting potential, but an action potential only occurs when the depolarization reaches the threshold level.

Action potential in a neuron, showing depolarization, in which the cell’s internal charge becomes less negative (more positive), and repolarization, where the internal charge returns to a more negative value.

The main difference between the two is: depolarization is described as the loss of resting membrane potential as a result of the alteration of the polarization of cell membrane. repolarization is described as the restoration of the resting membrane potential after every depolarization event.

Early repolarization (ER), also recognized as “J-waves” or “J-point elevation”’ is an electrocardiographic abnormality consistent with elevation of the junction between the end of the QRS complex and the beginning of the ST segment in 2 contiguous leads[9,10].

Repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels. Hyperpolarization occurs due to an excess of open potassium channels and potassium efflux from the cell.

Repolarization is the return of the ions to their previous resting state, which corresponds with relaxation of the myocardial muscle. 8. Depolarization and repolarization are electrical activities which cause muscular activity.

These results are in agreement with the hypothesis that the slow phase of repolarization is due to an inward current generated by Na+-Ca2+ exchange, as latter mechanism is known to be sensitive to the intracellular and extracellular concentrations of both Na+ and Ca2+.

Normal sinus rhythm is defined as the rhythm of a healthy heart. It means the electrical impulse from your sinus node is being properly transmitted. In adults, normal sinus rhythm usually accompanies a heart rate of 60 to 100 beats per minute. However, normal heart rates vary from person to person.

In the heart, electrical activity (depolarization and repolarization) proceeds in a sequential manner. From the SA node, the wave of depolarization moves through both atria (P wave), resulting in atrial contraction.

Phase zero

A wave of depolarization traveling toward a positive electrode results in a positive deflection in the ECG trace. A wave of depolarization traveling away from a positive electrode results in a negative deflection. A wave of repolarization traveling away from a positive electrode results in a positive deflection.

Normal ECG values for waves and intervals are as follows: RR interval: 0.6-1.2 seconds. P wave: 80 milliseconds. PR interval: 120-200 milliseconds.

The P wave indicates atrial depolarization. The P wave occurs when the sinus node, also known as the sinoatrial node, creates an action potential that depolarizes the atria.

The Abnormal P wave Elevation or depression of the PTa segment (the part between the p wave and the beginning of the QRS complex) can result from atrial infarction or pericarditis. If the p-wave is enlarged, the atria are enlarged.

An ECG Can Recognize the Signs of Blocked Arteries. Since the test identifies anomalies of heart rhythm, impaired blood flow to the heart, otherwise known as ischemia, says WebMD, can also be identified. The electrical signals may be fainter or diverge from expected patterns.

A person with heart disease may have a normal ECG result if the condition does not cause a disturbance in the electrical activity of the heart. Other diagnostic methods may be recommended if heart disease is suspected.

An echocardiogram is a common test. It gives a picture of your heart using ultrasound. It uses a probe either on your chest or sometimes can be done down your oesophagus (throat). It helps your doctor check if there are any problems with your heart’s valves and chambers, and see how strongly your heart pumps blood.

Even though lying on your left side may change your heart’s electrical activity, there’s no evidence that it increases your risk of developing a heart condition if you don’t already have one.

What do EF results mean? A normal LVEF reading for adults over 20 years of age is 53 to 73 percent. An LVEF of below 53 percent for women and 52 percent for men is considered low. An RVEF of less than 45 percent is considered a potential indicator of heart issues.

In end stage heart failure, the body can no longer compensate for the lack of blood the heart pumps….A person with end stage heart failure may experience symptoms of cardiovascular disease, including :

• difficulty breathing.
• fatigue (lack of energy)
• abdominal pain.
• severe, unexplained weight loss.
• irregular heartbeat.

Neurons can undergo depolarization in response to a number of stimuli such as heat, chemical, light, electrical or physical stimulus. These stimuli generate a positive potential inside the neurons. When the positive potential becomes greater than the threshold potential, it causes the opening of sodium channels.

The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage-gated sodium channels into a neuron. As additional sodium rushes in, the membrane potential actually reverses its polarity.

The T wave represents ventricular repolarization. Generally, the T wave exhibits a positive deflection. The reason for this is that the last cells to depolarize in the ventricles are the first to repolarize.

An ECG Can Recognize the Signs of Blocked Arteries. Unfortunately, the accuracy of diagnosing blocked arteries further from the heart when using an ECG decrease, so your cardiologist may recommend an ultrasound, which is a non-invasive test, like a carotid ultrasound, to check for blockages in the extremities or neck.

Absence of the P wave with a flat baseline may indicate: Fine atrial fibrillation. Sinoatrial arrest (with a secondary escape rhythm)

It represents the electrical depolarization of the atria of the heart. It is typically a small positive deflection from the isoelectric baseline that occurs just before the QRS complex. It can sometimes have abnormalities in morphology or timing that can be indicative of significant clinical pathology.

Absence of P waves suggests either. No normal atrial depolarization, e.g., atrial fibrillation, atrial standstill. The P waves are hidden within the QRS complexes, e.g., ventricular tachycardia, junctional tachycardia.

♥P waves can also be absent if the impulse does not travel up into the atria. A Premature Junctional Contraction is an early beat that occurs prior to the next sinus beat. Similar to a PAC EXCEPT P wave is inverted on the PJC!!

When a person has a normal sinus rhythm on their EKG, these beats are in a regular, orderly rhythm. Each should look like the previous and will be as evenly spaced with each other.

ECG features of normal sinus rhythm

1. Regular rhythm at a rate of 60-100 bpm (or age-appropriate rate in children)
2. Each QRS complex is preceded by a normal P wave.
3. Normal P wave axis: P waves upright in leads I and II, inverted in aVR.
4. The PR interval remains constant.

Symptoms can include:

1. A racing or fluttering heart.
2. Shortness of breath.
3. Sweating.
4. Headache.
5. Dizziness or lightheadedness.
6. Fainting.

These junctional tachycardias are most often observed in the setting of digitalis toxicity, recent cardiac surgery, acute myocardial infarction, or isoproterenol infusion. Accelerated junctional rhythm is present in this patient. Note the inverted P waves that precede each QRS complex, with a rate of 115 bpm.

What type of rhythm would be present if abnormal impulses are ignored? Retrograde firing means the electrical firing over the heart moves backwards. A fast, irregular heartbeat sensation felt by the patient is known as pacemaker spikes.

Symptomatic junctional rhythm is treated with atropine.

AV nodal junctional rhythms generally are well tolerated; however, bradycardia for prolonged periods often causes symptoms such as dizziness and presyncope or, rarely, frank syncope in younger patients.

Sinus rhythm refers to the rhythm of your heart beat, determined by the sinus node of your heart. The sinus node creates an electrical pulse that travels through your heart muscle, causing it to contract, or beat. You can think of the sinus node as a natural pacemaker.

Definition of Junctional Escape Rhythm

1. A junctional rhythm with a rate of 40-60 bpm.
2. QRS complexes are typically narrow (< 120 ms).
3. No relationship between the QRS complexes and any preceding atrial activity (e.g. P-waves, flutter waves, fibrillatory waves).

No pharmacologic therapy is needed for asymptomatic, otherwise healthy individuals with junctional rhythms that result from increased vagal tone. In patients with complete AV block, high-grade AV block, or symptomatic sick sinus syndrome (ie, sinus node dysfunction), a permanent pacemaker may be needed.

A junctional rhythm occurs when the electrical activation of the heart originates near or within the atrioventricular node, rather than from the sinoatrial node. A junctional rhythm is normally slow — less than 60 beats per minute. When faster, it is referred to as an accelerated junctional rhythm.

The ventricular rate is generally faster than the atrial rate except when an accelerated junctional rhythm develops in the presence of atrial tachycardia, atrial fibrillation, or atrial flutter. An accelerated junctional rhythm is seen predominantly in patients with heart disease.