Bundle Branch Blocks

In BBB, one or the other (or both) of these bundle branches no longer conduct electrical impulses normally. This can occur from disease or damage to one of the bundle branches, or it may occur for no apparent reason in completely healthy people. When the electrical impulse is delayed in reaching its respective ventricle, the delay shows up as a distinctive pattern on the ECG called a BBB. The chief effect of a BBB is to disrupt the normal, coordinated and simultaneous contraction of the two ventricles. The contraction of one ventricle (the one whose bundle branch is blocked) occurs slightly after the contraction of the other.

People with BBB usually will have either right bundle branch block (RBBB) or left bundle branch block (LBBB), depending on which of the two bundle branches is "blocked." Sometimes both bundle branches are affected, and the BBB pattern on the ECG is not clearly identifiable as either right or left BBB - in this case, the BBB is referred to as an intraventricular conduction delay (IVCD).

Wolff-Parkinson-White

Wolff–Parkinson–White syndrome (WPW) is one of several disorders of the electrical system of the heart that are commonly referred to as pre-excitation syndromes.

WPW is caused by the presence of an abnormal accessory electrical conduction pathway between the atria and the ventricles. Electrical signals traveling down this abnormal pathway (known as the bundle of Kent) may stimulate the ventricles to contract prematurely, resulting in a unique type of supraventricular tachycardia referred to as an atrioventricular reciprocating tachycardia.

WPW ECG Examples:

Pacemakers

ECG Training

Hyperkaelemia ECG Features

With mild to moderate hyperkalemia, there is reduction of the size of the P wave and development of peaked T waves. Severe hyperkalemia results in a widening of the QRS complex, and the ECG complex can evolve to a sinusoidal shape. There appears to be a direct effect of elevated potassium on some of the potassium channels that increases their activity and speeds membrane repolarization. Also, (as noted above), hyperkalemia causes an overall membrane depolarization that inactivates many sodium channels. The faster repolarization of the cardiac action potential causes the tenting of the T waves, and the inactivation of sodium channels causes a sluggish conduction of the electrical wave around the heart, which leads to smaller P waves and widening of the QRS comple.

To be completed

Brugada Syndrome

To be completed

Basic Electrophysiology

The heart’s electrical activity is represented on the monitor or ECG tracing by three basic waveforms: the P wave, the QRS complex, and the T wave. A U wave is sometimes present.

Between the waveforms are the following segments and intervals: the PR interval, the ST segment, and the QT interval. Although the letters themselves have no special significance, each component represents a particular event in the depolarization–repolarization cycle.

Calculating the Heart Rate

There are several methods for determining heart rate. Our first method is simple. Count the number of QRS complexes over a 6 second interval. Multiply by 10 to determine heart rate. This method works well for both regular and irregular rhythms. In the first image, we can count 5 QRS complexes, so the heart rate is 50.

The second method uses small boxes. Count the number of small boxes for a typical R-R interval. Divide this number into 1500 to determine heart rate.

ECG tracings are recorded on grid paper. The horizontal axis of the 

ECG paper records time, with black marks at the top indicating 3 second intervals. Each second is marked by 5 large grid blocks. Thus each large block equals 0.2 second. The vertical axis records EKG amplitude (voltage). Two large blocks equal 1 millivolt (mV). Each small block equals 0.1 mV. Within the large blocks are 5 small blocks, each representing 0.04 seconds.