TACHYCARDIA,
FIBRILLATION, AND ATRIAL FLUTTER
PAROXYSMAL TACHYCARDIA
Paroxysmal atrial tachycardia (PAT) is caused by a pace maker in the atria that gives rise to rapid regular impulses at a rate above 100 beats/min, often as much as 180 beats/min (see Plate 2-27). P waves can usually be identified, although in some cases the P and T waves fall on each other. The R-R intervals are regular. PAT is characterized by an abrupt beginning and ending. The onset and end often occur within the course of a single beat. Carotid sinus pressure may cause a sudden reversion to sinus rhythm, which is diagnostic of PAT.
Paroxysmal Atrial
Tachycardia with Block
It is important
to recognize PAT with block because it may be caused by digitalis intoxication,
in which case the digitalis should be withdrawn. The condition is the same as
the PAT just described.
This
disturbance is characterized by inverted P waves in leads II, III, and aVF
because of retrograde atrial conduction. The P waves fall before, within, or
after the QRS complexes. Retrograde conduction may occur. Paroxysmal nodal
tachycardia often is caused by disease of the A-V node.
Ventricular
tachycardia is caused by rapid impulse formation in a ventricle. The arrhythmia
is serious and often associated with the toxic effects of digitalis and many
antiarrhythmics (e.g., sotalol), or it may be caused by serious organic cardiac
disease. The ventricular rate is more rapid than the atrial rate, and close
inspection of the tracing allows identification of occasional P waves occurring
at the basic atrial rate. The ventricular contractions are generally more than
150 beats/min and may be greater than 200 beats/min. The QRS complexes are
wide, with T waves that are discordant with the QRS complexes, and the P-R
intervals are not identical.
Atrial
fibrillation (AF) is the most common arrhythmia on hospital admission in older
patients AF is caused by the presence of multiple islands of abnormal
myocardium in various states of refractoriness, so that the atrial
depolarization wave must wind its way in and out of these islands of tissue,
resulting in electric potentials of low voltage with variable directions. Only
some of these impulses are transmitted through the
A-V node; thus all the R-R intervals are different because of the irregularity
of conduction (see Plate 2-27).
Rheumatic heart
disease, hyperthyroidism, and arterio-sclerotic
heart disease are common causes of AF. There are no consistently identifiable P
waves in the tracing with AF. The ventricular rate may be rapid or slow,
depending on the degree of conduction through the A-V node and the presence of
heart failure or digitalis and other drugs that slow or accelerate conduction.
If the ventricular rate is rapid and heart failure is present, the rate can be
slowed greatly by beta blockers, calcium antagonists, and digitalis. Sinus
rhythm can be achieved by electrical or chemical cardioversion and
antiarrhythmics as well as by catheter-based ablation of atrial tissue in the
pulmonary vein or other sites of origin of the arrhythmia.
ATRIAL
FLUTTER
Atrial flutter
is caused by a circus movement or a low atrial pacemaker that fires regularly
at a rapid rate, usually about 220 beats/min (see Plate 2-27). Often there is a variable block at the A-V node, and only every
other beat, or every third or fourth beat, is transmitted to the ventricles. A
clinical clue to the diagnosis of atrial flutter is a ventricular rate of 150
beats/min. This usually means atrial flutter with 2 : 1 block. In leads II,
III, and aVF, usually inverted P waves are followed by atrial
T waves, or continuous atrial activity results from the circus movement. These
waves have a sawtooth appearance.
Arteriosclerotic
heart disease, hyperthyroidism, and rheumatic heart disease are common causes
of atrial flutter. This is a macro–reentrant arrhythmia and can be ablated with
radiofrequency energy applied in the right atrium.
VENTRICULAR
FIBRILLATION
Multiple
periodic ventricular pacemakers result in erratic depolarization of the
ventricles, producing an ECG that resembles distorted sine waves irregular in
amplitude and duration. The waves may be of high or low voltage. With
ventricular fibrillation there is no effective pumping of the heart. Severe
organic cardiac disease or the toxic effects of digitalis or antiarrhythmics
that prolong the Q-T interval can produce a similar condition. The treatment of
choice is immediate electrical defibrillation (see Plate 2-27).
