Electrical alternans is a broad term that describes alternate-beat variation in the direction, amplitude, and duration of any component of the ECG waveform (ie, P, PR, QRS, R-R, ST, T, U)
It was first recognized by Hearing in 1909 and further characterized by Sir Thomas Lewis in 1910 as occurring “either when the heart muscle is normal but the heart rate is very fast or when there is serious heart disease and the rate is normal.”
Kalter and Schwartz first identified electrical alternans on surface ECG in 1948
Electrical alternans must be distinguished from mechanical alternans (eg, pulsus alternans), although both may coexist
It was first recognized by Hearing in 1909 and further characterized by Sir Thomas Lewis in 1910 as occurring “either when the heart muscle is normal but the heart rate is very fast or when there is serious heart disease and the rate is normal.”
Kalter and Schwartz first identified electrical alternans on surface ECG in 1948
Electrical alternans must be distinguished from mechanical alternans (eg, pulsus alternans), although both may coexist
The pathophysiologic mechanisms that cause electrical alternans can be divided into 3 categories:
-Repolarization alternans (ST, T, U alternans)
-Conduction and refractoriness alternans (P, PR, QRS alternans)
-Alternans due to cardiac motion
Electrical Alternans Associated with cardiac motion is due to alternation in the position of the heart with relation to recording electrodes.
The most common underlying disorder is an enlarged pericardial sac; however, not all pericardial effusions cause electrical alternans.
The presence of pericardial disease and total electrical alternans (P, QRS, and T wave) frequently suggests cardiac tamponade, but total electrical alternans is seen in only 5-10% of patients with cardiac tamponade.
Heart movement in patients with hypertrophic cardiomyopathy also may result in electrical alternans of this type .
Whenever what appears to be electrical alternans is not due to a large pericardial effusion, then pseudoelectrical alternans should be considered. Pseudoelectrical alternans is due to alternation in axis or amplitude because of events that alter conduction and do not alter the physical orientation of the heart.
In 1978, Klein, Segni and Kaplinsky coined the term ‘pseudoelec- trical alternans’ in a case report of intermittent left anterior hemiblock, in which the axis shifted every other beat due to the development of alternating normal and then leftward axis shift, presumably related to procaina- mide therapy.
Unfortunately, some literature defining interchangeably as true electrical alternans is a repolarization or conduction abnormality of the Purkinje fibers or myocardium.
Electrical alternans due to cardiac motion is effectively artifact, as the heart swings in relation to the chest wall and electrodes, with a period twice that of the heart rate. However, tamponade related electrical alternans is the true one .
Electrical alternans due to cardiac motion is effectively artifact, as the heart swings in relation to the chest wall and electrodes, with a period twice that of the heart rate. However, tamponade related electrical alternans is the true one .
Exclusively in Dr.Nabil Paktin Cardiology Notes
