Download Atrial Arrhythmias with Low Amplitude P waves

Atrial Arrhythmias with Low Amplitude P waves*
Richard K. Albert, M.D., I. Peter Roberts, M.D., and
Philip B. Oliva, M.D., F.C.C.P.
he identification of supraventricular arrhythmias
Tfrom
a standard 12-lead electrocardiogram
(ECG) is sometimes difficult. Intra-atrial electrocardiography' and His bundle recordings2 have
been demonstrated to be of value under these circumstances. The following patient is of interest because he displayed two atrial arrhythmias without
diagnostic P wave activity on the surface ECG.
A 78-year-old black man with an eight-year history of
atrial fibrillation was admitted to the hospital with nausea,
'From the Department of Medicine, Division of Cardiolo ,
Denver General Hospital and the University of ~ o l o r a y o
School of Medicine, Denver.
Reprint requests: Dr. Oliva, Denver General Hospital, Denver
80204
vomiting and visual complaints. He was taking 0.25 mg
digoxin daily. The ECC was interpreted as atrial fibrillation
with A-V dissociation and a junctional rhythm (Fig 1). At
other times the regular ventricular rate was interrupted by
pauses which were thought to be due to subjunctional exit
block.3 A digoxin level was 6.6 ng/ml. Because of symptoms
referable to the slow ventricular rate and a poor response to
atropine and isoproterenol ( Isuprel ) therapy, a temporary
transvenous pacemaker was inserted. During this procedure a
His bundle recording was obtained. The initial recording
appeared to confirm the impression of atrial fibrillation with
A-V dissociation and a junctional rhythm ( Fig 2 ) . However,
a bipolar right atrial eledrogram revealed the true arrhythmia to be paroxysmal atrial tachycardia (PAT) with 2: 1
block. The bipolar catheter electrodes were then repositioned
near the His bundle and a recording was obtained showing
atrial, His bundle, and ventricular depolarizations, with a
Wenckebach phenomenon in the A-V node ( Fig 3).
The patient was discharged without digitalis therapy, but
FIGURE1. Rhythm strip interpreted as atrial fibrillation with A-V dissociation and junctional
tachycardia. Concurrent digoxin level was 6.6 ng/ml.
L .T.
12.:7: 72
HBE
H
FIGURE2. His bundle electrogram also interpreted as atrial fibrillation with A-V dissociation
and junctional rhythm. Note absence of visible atrial activity.
CHEST, VOL. 65, NO. 1, JANUARY, 1974
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ATRIAL ARRHYTHMIAS WITH LOW AMPLITUDE P WAVES
digoxin, 0.25 mg daily, was given on an outpatient basis.
Several weeks later the ECG revealed an absence of P waves,
with an irregular ventricular rate of 120 per minute. Because
of the previous findings of PAT with block and low amplitude
P waves, an intra-atrial electrogram was repeated. This time
there was atrial flutter (atrial rate 335 per minute), with a
varying ventricular response (not shown). The digoxin level
was 1.5 ng/ml. With further digitalis treatment the venhicular rate decreased to about 100 and he was discharged on
digoxin, 0.25 mg, alternating with 0.125 mg daily.
Intra-atrial electrocardiography was used to demonstrate atrial activity, which was poorly visible on
the standard 12-lead ECG. Atrial activity is sometimes obscured by the QRS complexes and T waves
when the ventricular rate is rapid, but in this instance the ventricular rate was only 90 beats per
minute. Low amplitude P waves are also observed in
hyperkalemia;' however, the patient's serum potas-
sium level was repeatedly normal. The low amplitude P waves were poorly visible not only on the
surface ECG but also on the initial intracardiac
recording from the region of the His bundle. The
intra-atrial electrogram, however, identified the regular atrial activity. Thus, even a His bundle electrogram may occasionally fail to reveal atrial activity.
al: A simple tech1 Vogel JHK, Tabari K, Averill KH.
nique for identifying P waves in complex arrhythmias. Am
Heart J 67: 158,1967
2 Goldreyer BN: Intracardiac electrocardiography in the
analysis and understanding of cardiac arrhythmias. Ann
Intern Med 77: 117, 1972
3 Kastor JA, Yurchak PM: Recognition of digitalis intoxication in the presence of atrial fibrillation. Ann Intern Med
67: 1045.1967
4 Surawia B: Relationship between electrocardiogram and
electolytes. Am Heart J 73:814-834, 1967
CHEST, VOL. 65, NO. 1, JANUARY, 1974
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