the t wave of an electrocardiogram corresponds to what electrical activity?

Lesson 5: ECG I INTRODUCTION

The main function of the eye is to pump claret through ii circuits:

1. Pulmonary circuit: through the lungs to oxygenate the blood and remove carbon dioxide; and

2. Systemic circuit: to evangelize oxygen and nutrients to tissues.

Because the middle moves blood through 2 separate circuits, it is sometimes described as a dual pump.

In order to crush, the eye needs three types of cells:

1. Rhythm generators, which produce an electrical signal (SA node or normal
 pacemaker);

ii. Conductors to spread the pacemaker indicate; and

three. Contractile cells (myocardium) to mechanically pump blood.

The Electrical and Mechanical Sequence of a Heartbeat

The heart has specialized pacemaker cells that get-go the electrical sequence of depolarization and repolarization. This property of cardiac tissue is called inherent rhythmicity or automaticity. The electric signal is generated past the sinoatrial node (SA node) and spreads to the ventricular muscle via item conducting pathways: internodal pathways and atrial fibers, the atrioventricular node (AV node), the bundle of His, the right and left packet branches, Purkinje fibers.

When the electrical signal of a depolarization reaches the contractile cells, they contract. When the repolarization indicate reaches the myocardial cells, they relax. Thus, the electric signals crusade the mechanical pumping activity of the heart.

The SA node is the normal pacemaker of the heart, initiating each electrical and mechanical cycle. When the SA node depolarizes, the electric stimulus spreads through atrial muscle causing the muscle to contract. Thus, the SA node depolarization is followed by atrial contraction.

The SA node impulse also spreads to the atrioventricular node (AV node) via the internodal fibers. (The moving ridge of depolarization does not spread to the ventricles right away because there is nonconducting tissue separating the atria and ventricles.) The electrical signal is delayed in the AV node for approximately 0.20 seconds when the atria contract, and then the signal is relayed to the ventricles via the bundle of His, right and left bundle branches, and Purkinje fibers. The Purkinje fibers, relay the electric impulse directly to ventricular muscle, stimulating the ventricles to contract (ventricular systole). Repolarization of the SA node is also spread throughout the atria, and then the ventricles, starting the relaxation stage (ventricular diastole).

Although the heart generates its own crush, the eye charge per unit (!2eats I2er_inute or BPM) and strength of contraction of the middle are modified by the sympathetic and parasympathetic divisions of the autonomic nervous system.

 The sympathetic system acts as an accelerator, speeding upward and increasing the contractile force of the eye. Whe-never oxygen demands increase, east.g., during exercise or if blood pressure drops, the sympathetic input increases, causing heart rate and forcefulness of contraction to increase. Sympathetic influence increases during inhalation.

 The parasympathetic input acts like a brake, slowing downwardly the heart. When you relax, the parasympathetic input becomes dominant and the center charge per unit slows. Parasympathetic influence increases during exhalation.

The Electrocardiogram (ECG)

Just equally the electrical activeness of the pacemaker is communicated to the cardiac muscle, "echoes" of the depolarization and repolarization of the centre are sent through the rest of the body. By placing a pair of very sensitive receivers (electrodes) on other parts of the body, the echoes of the eye's electrical activity can be detected. The tape of the electrical bespeak is called an electrocardiogram (ECG). You lot tin can infer the eye�s mechanical activeness from the ECG.

The electrical events of the heart are usually recorded on the ECG as a design of a baseline broken by a P wave, a QRS complex, and a T moving ridge.

The baseline (isoelectric line) is a straight line on the ECG. It is the bespeak of divergence for the electrical activity of depolarizations and repolarizations of the cardiac cycles.

 The P wave results from atrial depolarization.

 The QRS complex is a result of ventricular depolarization and indicates the start of ventricular wrinkle.

 The T wave results from ventricular repolarization and signals the beginning of ventricular relaxation.

The electrical betoken for atrial repolarization is masked past the larger QRS complex.

In addition to the wave components of the ECG, there are intervals and segments.

An interval is part of the ECG containing at least one wave and a straight line. For example, the PR interval includes the P wave and the connecting line earlier the QRS complex. The PR interval represents the time it takes for the impulse sent from the SA node to travel to the ventricles.

Segments but refer to a period of time from the stop of one moving ridge to the offset of the next wave. For example, the PR segment represents the fourth dimension of AV nodal delay and transmission to the ventricles.

Because the ECG reflects the electrical activity, it is a useful "moving picture" of heart activity. If there are interruptions of the electrical betoken generation or transmission, the ECG changes. These changes can be useful in diagnosing changes inside the center.

The particular system of two electrodes (i positive, one negative) with respect to a third electrode (the ground) is called a pb. The positions of electrodes for the different leads have been standardized. For this lesson, you will record from Atomic number 82 Ii, which has a positive electrode on the left ankle, a negative electrode on the correct wrist, and the ground electrode on the right ankle. Typical Lead Two values are given in Table 5.ane.

Table v.ane Normal Pb Ii ECG Values

Phase	DURATION (second)	Aamplitude (millivolt)
Pwave	0.06-0.11	<0.25
P-R interval	0.12-0.20
P-R segment	0.08
QRS complex (R)	<0.12	0.8 - 1.2
S-T segment	0.12
Q-T interval	0.36-0.44
Twave	0.16	<0.five

The average resting centre charge per unit for adults is approximately seventy beats/min Slower heart rates are typically found in individuals who regularly exercise. Athletes are able to pump plenty claret to meet the demands of the trunk with resting heart rates as low as 50  beats/min. Athletes tend to develop larger hearts, peculiarly the muscle in the left ventricle a status known as "left ventricular hypertrophy." Because of their larger and more efficient hearts, athletes as well showroom other differences in their ECGs. For instance, low centre rate and hypertrophy exhibited in sedentary individuals can be an indication of failing hearts but these changes are "normal" for well trained athletes.

In this lesson, y'all volition record the ECG nether four conditions. Because ECGs are widely used, bones elements have been standardized to simplify reading ECGs.   ECGs have standardized grids of lighter, smaller squares and, superimposed on the starting time grid, a second grid of darker and larger squares. The smaller grid always has fourth dimension units of 0.04 seconds on the ten-axis and the darker vertical lines are spaced 0.2 seconds apart. The horizontal lines represent amplitude in mV. The lighter horizontal lines are 0.1 mV apart and the darker grid lines stand for 0.5 mV (Fig. 5.2).

Two. EXPERIMENTAL OBJECTIVES

1 ) To get familiar with the electrocardiograph as a primary tool for evaluating electrical events inside the center.

2) To correlate electric events as displayed on the ECG with the mechanical events that occur during the cardiac cycle.

3) To notice rate and rhythm changes in the ECG associated with body position and breathing.

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Source: https://www.csun.edu/~vcpsy00i/dissfa01/xECG_Lesson.html

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