Tuesday, 3 October 2017

right ventricular wall infarction






Basic ecg rhythm strips


Einthoven's triangle

Einthoven's triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis. The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed. It is named after Willem Einthoven, who theorized its existence.
Einthoven used these measuring points, by immersing the hands and foot in pails of salt water, as the contacts for his string galvanometer, the first practical ECG machine.

Electrodes may be placed distally or proximally on the limb without affecting the recording. The leg electrode acts as a grounding lead, and either the right or left leg can be used as a grounding lead without an effect on the ECG results.
Each lead measures the electric field created by the heart during the depolarization and repolarization of myocytes. The electric field can be represented as a vector that changes continuously and can be measured by recording the voltage difference between electrodes.

Though Einthoven's triangle is no longer used in contemporary ECGs, Einthoven's triangle can be helpful in the identification in incorrect placement of leads. (Incorrect placement of leads can lead to error in the recording, which can ultimately lead to misdiagnosis.) If the arm electrodes are reversed, lead I changes polarity, causing lead II and lead III to switch. If the right arm electrode is reversed with the leg's electrode, lead II changes polarity, causing lead I to become lead III, and vice versa. Reversal of the left arm and leg causes a change in polarity of lead III and switching of leads I and II.



Wednesday, 16 November 2016

Pericarditis





Acute pericarditis is a type of pericarditis (inflammation of the sac surrounding the heart, the pericardium) usually lasting less than 6 weeks. It is by far the most common condition affecting the pericardium.

Typical ECG changes in acute pericarditis includes:
  • stage 1 - diffuse, positive, ST elevations with reciprocal ST depression in aVR and V1. Elevation of PR segment in aVR and depression of PR in other leads especially left heart V5, V6 leads indicates atrial injury.
  • stage 2 - normalization of ST and PR deviations
  • stage 3 - diffuse T wave inversions (may not be present in all patients)
  • stage 4 - ECG becomes normal OR T waves may be indefinitely inverted
The two most common clinical conditions where ECG findings may mimic pericarditis are acute myocardial infarction (AMI) and generalized early repolarization.

Parasystole



Parasystole is a kind of arrhythmia caused by the presence and function of a secondary pacemaker in the heart, which works in parallel with the SA node. Parasystolic pacemakers are protected from depolarization by the SA node by some kind of entrance block. This block can be complete or incomplete.
Parasystolic pacemakers can exist in both the atrium or the ventricle. Atrial parasystolia are characterized by narrow QRS complexes.

There are two forms of ventricular parasystole, fixed parasystole and modulated parasystole. Fixed ventricular parasystole occurs when an ectopic pacemaker is protected by entrance block, and thus its activity is completely independent from the sinus pacemaker activity. Hence, the ectopic pacemaker is expected to fire at a fixed rate. Therefore, on ECG, the coupling intervals of the manifest ectopic beats will wander through the basic cycle of the sinus rhythm. Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are:
  • the presence of variable coupling intervals of the manifest ectopic beats;
  • inter-ectopic intervals that are simple multiples of a common denominator;
  • fusion beats.