This is known as an S wave and represents depolarisation in the Purkinje fibres. The S wave travels in the opposite direction to the large R wave because, as can be seen on the earlier picture, the Purkinje fibres spread throughout the ventricles from top to bottom and then back up through the walls of the ventricles.
| P wave | T wave |
|---|
| Represents atrial depolarization or atrial systole | Represents ventricular repolarization or ventricular relaxation |
| During this phase, the impulse of contraction is generated by the SA node, causing atrial depolarization | During this phase, the ventricles relax and return to their normal state. |
Atrial and ventricular depolarization and repolarization are represented on the ECG as a series of waves: the P wave followed by the QRS complex and the T wave. By convention the first deflection in the complex, if it is negative, is called a Q wave. The first positive deflection in the complex is called an R wave.
The S wave is the first downward deflection of the QRS complex that occurs after the R wave. A large slurred S wave is seen in leads I and V6 in the setting of a right bundle branch block. The presence or absence of the S wave does not bear major clinical significance.
P-wave questions:
- Are they present?
- Do they occur regularly?
- Is there one P-wave for each QRS complex?
- Are the P-Waves smooth, rounded, and upright?
- Do all P-Waves have similar shapes?
Atrial depolarization initiates contraction of the atrial musculature. As the atria contract, the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular (AV) valves, leading to a rapid flow of blood into the ventricles.
The ECG is measured by placing a series of electrodes on the patient's skin – so it is known as the 'surface' ECG. The wave of electrical depolarisation spreads from the atria down though the IVS to the ventricles. So the direction of this depolarisation is usually from the superior to the inferior aspect of the heart.
The PR interval is the lapse of time between the onset of atria contraction to onset of ventricle contraction. The QRS complex represents ventricular depolarization (and atrial repolarization) or the journey through the electrical impulse from the Av-Node through the Purkinje network.
The most common cause of a dominant R wave in aVR is incorrect limb lead placement, with reversal of the left and right arm electrodes. This produces a similar pattern to dextrocardia in the limb leads but with normal R-wave progression in the chest leads. With LA/RA lead reversal: Lead I becomes inverted.
The precordial, or chest leads, (V1,V2,V3,V4,V5 and V6) 'observe' the depolarization wave in the frontal plane. Example: V1 is close to the right ventricle and the right atrium. Signals in these areas of the heart have the largest signal in this lead. V6 is the closest to the lateral wall of the left ventricle.
An ECG rhythm will appear upside-down if the mobile device is not properly oriented while the data is being acquired. You may invert an ECG that has previously been recorded by tapping the screen while reviewing the ECG in the Kardia app, and tapping the 'Invert' button that appears in the bottom right corner.
The areas represented on the ECG are summarized below: V1, V2 = RV. V3, V4 = septum. V5, V6 = L side of the heart. Lead I = L side of the heart.
R-wave amplitude in aVL should be ≤ 12 mm. R-wave amplitude in leads I, II and III should all be ≤ 20 mm. If R-wave in V1 is larger than S-wave in V1, the R-wave should be <5 mm.
The QRS complex is ventricular depolarization. It is typically much wider than the ventricular depolarization that generates the QRS. Sometimes it is upside down (inverted). Sometimes half of it is upside down and the other half upright; this is called biphasic.
If the leftward vector decreases in magnitude, it will show up on the surface ECG as a higher amplitude rightward depolarization. This is the mechanism by which decreased muscle mass can result in a tall R wave in V1. The common etiology is a posterior myocardial infarction (MI).
ECG – A Pictorial Primer. In right chest leads V1 and V2, the QRS complexes are predominantly negative with small R waves and relatively deep S waves because the more muscular left ventricle produces depolarization current flowing away from these leads. In V1 the QRS are positive with tall R waves.
A pathologic Q wave. Pathologic Q waves are a sign of previous myocardial infarction. They are the result of absence of electrical activity. A myocardial infarction can be thought of as an elecrical 'hole' as scar tissue is electrically dead and therefore results in pathologic Q waves.
Bundle branch block is a condition in which there's a delay or blockage along the pathway that electrical impulses travel to make your heart beat. It sometimes makes it harder for your heart to pump blood efficiently through your body.
ventricular depolarization
Doctors usually diagnose RBBB by using an electrocardiogram (EKG). This is a painless test that involves placing stickers called leads around your chest. The leads conduct electricity. They're connected to wires that sense the electrical impulses of your heart and trace your heart's rhythm.
Tall QRS complexes are usually caused by hypertrophy of one or both ventricles, or by an abnormal pacemaker or aberrantly conducted beat. • Low voltage or abnormally small QRS complexes may be seen in obese patients, hyperthyroid patients and pleural effusion.
Causes of ST Depression
- Myocardial ischaemia / NSTEMI.
- Reciprocal change in STEMIPosterior MI.
- Digoxin effect.
- Hypokalaemia.
- Supraventricular tachycardia.
- Right bundle branch block.
- Right ventricular hypertrophy.
- Left bundle branch block.
Biphasic QRS complex is a complex when there are 2 waves present in a QRS complex.
P-waves are compression waves that apply a force in the direction of propagation. On the other hand, S-waves are shear waves, which means that the motion of the medium is perpendicular to the direction of propagation of the wave. The energy is thus less easily transmitted through the medium, and S-waves are slower.
S-Waves. S-waves are transverse waves because they vibrate the ground in a the direction "transverse", or perpendicular, to the direction that the wave is traveling. As a transverse wave passes the ground perpendicular to the direction that the wave is propagating. S-waves are transverse waves.
Body waves travel through the body of a planet. Surface waves travel along the surface. There are two types of body waves: P-waves travel fastest and through solids, liquids, and gases; S-waves only travel through solids. Surface waves are the slowest, but they do the most damage in an earthquake.
In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. In rock, S waves generally travel about 60% the speed of P waves, and the S wave always arrives after the P wave.
P waves travel through rock the same way that sound waves do through air. That is, they move as pressure waves. When a pressure wave passes a certain point, the material it is passing through moves forward, then back, along the same path that the wave is traveling. P waves can travel through solids, liquids and gases.
The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart. This number will be used to tell you how far your seismograph is from the epicenter of the earthquake. Measure the distance between the first P wave and the first S wave.
Four types of seismic waves| Specifications of all types of seismic waves.
- P- Waves (Primary waves)
- S- Waves (Secondary waves)
- L- Waves (Surface waves)
- Rayleigh waves.
S-waves cannot travel through liquids. When they reach the surface they cause horizontal shaking. Liquids don't have any shear strength and so a shear wave cannot propagate through a liquid. Think of a solid material, like a rock.
