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PATHOGENESIS AND PREVENTION OF NECROSIS IN THE CARDIOVASCULAR
SYSTEM
¹Murodullayeva Mohinur
²Ahmedov Abbos
³Aminov Azimjon
Samarkand State Medical University, DKTF, Department of Internal Medicine, Cardiology and
Functional Diagnostics, 2nd year clinical residents
https://doi.org/10.5281/zenodo.14864420
Introduction:
A standard electrocardiogram is a 12-lead representation of the electrical
activity of the heart, representing the difference in electrical potential between positive and
negative electrodes placed on the limbs and chest. Six of these leads are vertical (taken from leads
I, II, and III located on the front and electrodes located on the limbs - aVR, aVL, aVF) and 6 are
horizontal (located in the precordial region - V1, V2, V3, V4, V5, and V6). The 12-lead ECG can
be an important imaging test for establishing a number of cardiac diagnoses (see the ECG changes
interpretation chart), including
Conditions predisposing to syncope or sudden death (e.g., Brugada syndrome, long QT
syndrome, Wolff-Parkinson-White syndrome)
Standard components of an electrocardiographic complex
It is generally accepted to divide the ECG curve into the P wave, PR interval, QRS
complex, QT interval, ST segment, T wave, and U wave (see ECG waveform diagram).
P wave = reflects atrial depolarization. PR interval = time interval from the onset of atrial
depolarization to the onset of ventricular depolarization. QRS complex = ventricular
depolarization, consisting of Q, R, and S waves. QT interval = time between the onset of
ventricular depolarization and ventricular repolarization. RR interval = time interval between two
complexes. T wave = ventricular repolarization. ST segment + T wave (ST-T) = ventricular
repolarization. U wave = probably after ventricular depolarization (relaxation).
Research methods and materials:
Typically, the QRS interval is 0.07-0.10 seconds. A complex duration of 0.10-0.11
seconds, depending on the changes in the shape of the QRS complex, is considered to be an
incomplete bundle branch block or a nonspecific intraventricular conduction delay. An interval
duration of ≥ 0.12 seconds indicates a complete bundle branch block or a delay in intraventricular
conduction.
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Normally, the QRS axis is from 90 to -30 °. A value of the cardiac electrical axis from -30
° to -90 ° is considered a deviation of the cardiac electrical axis to the left and is observed in the
left anterior bundle branch block of the bundle of His (-60 °) and inferior myocardial infarction.
A value of the electrical axis of the heart from 90 ° to 180 ° is considered a deviation of the
electrical axis of the heart to the right; It is observed in any condition that leads to increased
pulmonary pressure and hypertrophy of the right ventricle of the heart (cor pulmonale, acute
pulmonary embolism, pulmonary hypertension) and sometimes occurs with a block of the right or
posterior branch of the left bundle of His.
QT interval
The time interval between the beginning of ventricular depolarization and the end of their
repolarization. The QT interval should be calculated taking into account the heart rate using the
following formula:
Research results:
Where QTc is the expected value of the QT interval and RR is the time interval between
two QRS complexes. All intervals are recorded in seconds. The normal range of QTc in adults is
350-450 ms in men and 360-460 ms in women. Prolongation of the QTc interval is closely
associated with the development of torsades de pointes. Determining the QTc interval is often
difficult because the end of the T wave is often poorly defined or there are many drugs that prolong
the QT interval (see CredibleMeds).
ST segment
The ST segment reflects the end of ventricular myocardial depolarization. Normally, it is
located horizontally on the isoline similar to the PR (or TP) interval or slightly shifted from the
isoline.
T wave
Reflects ventricular repolarization. It usually has the same direction as the QRS complex
(opposite direction (discordant) may indicate current or past MI); the T wave is usually flattened,
rounded, but may be low-amplitude in hypokalemia and hypomagnesemia, and sharp-edged in
hyperkalemia and hypocalcemia.
U wave
The U wave usually occurs in patients with hypokalemia, hypomagnesemia, or ischemia.
The U wave is often present in healthy individuals.
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The electrodes for right chest leads are placed on the right side of the chest wall in a mirror
image of the standard left chest electrodes. They are labeled V1R–V6R; sometimes only V4R is
used as the most sensitive lead for diagnosing right ventricular myocardial infarction.
For additional unipolar leads, electrodes can be placed in the 5th intercostal space, V7 near
the posterior axillary line, V8 near the midscapular line, and V9 at the left edge of the spine. These
leads are rarely used, but they can be especially useful in diagnosing true posterior myocardial
infarction.
Esophageal torsion
The esophageal lead is located significantly closer to the atrium than the external leads. It
is used when the P wave is not recorded on a standard ECG, as well as when it is necessary to
determine the electrical activity of the atria during tachycardia with a wide ventricular complex
(the need to check its atrial or ventricular variant) or if atrioventricular dissociation is suspected.
The esophageal lead can also be used for intraoperative monitoring of myocardial ischemia or for
determining atrial activity during cardioplegia. The patient swallows the lead, which is then
attached to a conventional electrocardiograph, most often to lead II port.
Continuous ST segment monitoring
Continuous ST segment monitoring is used to detect ischemia and severe arrhythmias.
Monitoring can be automated (special electronic monitors are available) or performed during
clinical analysis of a series of electrocardiograms. Indications include intensive care unit
monitoring in patients with worsening angina, post-operative monitoring, intraoperative
monitoring, and postoperative follow-up.
QT interval dispersion
The QT interval variance (the difference between the longest and shortest intervals on a
12-lead ECG) has been proposed as a method for assessing myocardial repolarization
heterogeneity. Increased variance (≥ 100 milliseconds) indicates electrical heterogeneity of the
myocardium due to ischemia or fibrosis, which increases the risk of reentrant arrhythmias and
sudden death. Variance may be a predictor of mortality risk, but is rarely measured because
measurement error is widespread and values often overlap between patients with heart disease and
healthy individuals, there are no limits to the possible error, and other risk criteria exist for these
conditions.
Results
: The use of event sensors allows for continuous monitoring of the patient for up to
30 days, during which time it is possible to detect rare rhythm disturbances that are missed during
24-hour Holter monitoring. The recorder can be activated by the patient during continuous
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operation or at the onset of symptoms. The device's memory allows you to store information about
events that occurred a few seconds before and after activation. The patient can send ECG data to
a doctor for interpretation by telephone or via satellite; Some recorders can automatically transmit
information about serious events. If the patient has significant events (for example, fainting) that
occur more often than once every 30 days, an event recorder can be implanted under the skin
(implantable loop recorder). It is activated by a small magnet. The battery life of the subcutaneous
recorder is several years.
Summary
: Some consumer-grade smartwatches take ECGs from the wrist. Smartwatches
are capable of detecting arrhythmias in real time and are being explored for use in this area.
Traditional CT and MRI scans are limited in their use because the heart is constantly
beating, but if the rhythm is regular and the heartbeat is monitored, faster CT and MRI techniques
provide diagnostic images of the heart. Sometimes patients are given medications (such as beta
blockers) to slow the heart rate during the test.
With ECG synchronization, the recorded (or reconstructed) image is synchronized with the
electrocardiogram (ECG), which allows data from different phases of the cardiac cycle to be
combined to create single images of the individual stages of heart contraction.
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