Download Atrial Flutter with Exit Block

Atrial Flutter with Exit Block
CHARLES J. HOMCY, M.D., BEVERLY LORELL, M.D.,
AND PETER M. YURCHAK, M.D.
SUMMARY The mechanism of atrial flutter is controversial. A 76-year-old woman with rheumatic heart
disease was referred to our clinic with an unusual rhythm disturbance which initially appeared to be classic
atrial flutter at a rate of 300 beats/min. Later tracings, however, demonstrated a rate exactly one-half that of
the earlier ECGs, with an identical p-wave morphology and vector. This latter rhythm Ilso behaved in a
manner expected for a flutter mechanism in that both spontaneously and with carotid pressure high-degree
atrioventricular block occurred without alteration of the underlying atrial mechanism. Finally, the two rates
interchanged spontaneously over several days without any significant interval changes in medical therapy.
These findings were initially explained as probable digoxin toxicity. The underlying mechanism, however,
was more likely atrial flutter with exit block and in this patient may have represented another facet of her sick
sinus syndrome. This unusual phenomenon is discussed in terms of previous reports and possible implications
for the mechanism of atrial flutter.
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been in atrial flutter or fibrillation throughout this
period. In the past 6 months, several emergency ward
visits have been precipitated by either severe dizziness,
a frank syncopal episode, or more frequently by
marked dyspnea. Each time, a rapid SVT intervened,
typically atrial flutter at a rate of 290 beats/min with
2:1 AV block (fig. 1). However, in September 1977,
an SVT at a rate of 145 beats/min with 2:1 AV block
was noted (fig. 2). Distinct p waves were present with a
constant PR interval. Intially, PAT with block was
diagnosed and we suspected digoxin toxicity.
However, the patient's digoxin level was 0.8 and 0.6
ng/ml (normal 1.2 ± 0.4 ng/ml) on two measurements and unchanged from previous levels when
the rhythm had been in atrial flutter. No interval
change in medications had been made. The serum
potassium level was stable at 4.0-4.5 mEq/l. During
the next few weeks, on several occasions, the rhythm
spontaneously reverted from atrial flutter at a rate of
290-300 beats/min with 2:1 AV block to SVT with
2:1 AV block and at times 1: 1 conduction. Each time
at the slower atrial rate of 145 beats/min, p-wave vector and morphology were identical to that noted with
atrial flutter at a rate of 290. In addition, on at least
two occasions, the atrial rate was exactly half that of
the flutter rate recorded before or just after its occurrence. Moreover, high-grade AV block occurred
spontaneously, as well as with carotid sinus pressure,
both during clear-cut atrial flutter at a rate of 290
beats/min (fig. 3) and with the SVT at a rate of 145
beats/min (fig. 4). The rhythm strip in figure 3 shows
the more classic "sawtooth" pattern characteristic of
ATRIAL FLUTTER is an enigmatic rhythm disturbance incompletely understood and often refractory to
a variety of therapies. As pointed out by Marriott,' no
clear-cut definition distinguishes flutter from other
forms of atrial tachycardia. Moreover, the development of a rapid supraventricular tachycardia with
atrioventricular (AV) block in a patient taking
digitalis leads to additional problems. The question
often arises as to whether this represents paroxysmal
atrial tachycardia (PAT) with block2 or more rarely,
atrial flutter as a manifestation of digoxin toxicity."
Recently an elderly patient presented to us with a
recurrent supraventricular tachycardia (SVT) with
several unusual features. The initial rhythm appeared
to be classic atrial flutter at a rate of 290-300
beats/min with 2:1 AV block. Subsequent tracings,
however, showed a rate of exactly half that of the initial rhythm, with an identical p-wave morphology and
vector. Although this latter rhythm was initially interpreted to be digoxin-related PAT with block, it
probably represented atrial flutter with a 2:1 exit
block from the flutter focus. The development of exit
block in atrial tachysystole simulating flutter has been
clearly described in one patient,5 and atrial tachycardia with exit block has been reported rarely.6 10 This
case is an example of a phenomenon only rarely
reported previously. It presented an intriguing
differential diagnosis in terms of possible digoxinrelated PAT with block.
Case Report
The patient was a 76-year-old white female treated
at Massachusetts General Hospital for several years.
For longer than 10 years, she has had documented
mild aortic regurgitation and mitral stenosis and has
flutter.
A low total and free T4 and a high thyrotropin were
documented during this same period, but the patient
was not treated initially because she had no symptoms
of hypothyroidism. In addition, considering her age
and underlying heart disease, we feared that more
refractory episodes of tachycardia would occur. Eventually we realized that these episodes of SVT did not
represent excessive digoxin therapy, and the digoxin
dose was increased from 0.25 mg/day to 0.375 mg/
day. The patient then developed higher degrees of AV
block with a ventricular response as slow as 30-40.
From the Cardiac Unit, Department of Medicine, Massachusetts
General Hospital, and Harvard Medical School, Boston,
Massachusetts.
Address for reprints: Charles J. Homcy, M.D., Massachusetts
General Hospital, Boston, Massachusetts 02114.
Received June 28, 1978; revision accepted March 13, 1979.
Circulation 60, No. 3, 1979.
711
CIRCULATION
712
VOL 60, No 3, SEPTEMBER 1979
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FIGURE 1. A trial flutter at a rate of 290-300 beats/min.
The tracing was darkened to illustrate the diminutive p
waves (arrows). The lead recordings are not simultaneous.
Alternate p waves are not seen in lead V1 in that they are
superimposed
on
the QRS complex.
Therefore, a permanent ventricular pacemaker was
implanted and the patient was maintained on digoxin
0.375 mg/day, resulting in a serum level of 1.0-1.2
ng/ml. Her rhythm is now predominantly v-paced,
with associated atrial flutter or SVT with high-degree
AV block.
The series of rhythm disturbances presented here illustrates at least three unusual features of atrial
flutter. First, the spontaneous development of apparent flutter with 2: 1 exit block from the flutter focus
was observed. That this was the mechanism underlying the observed tachycardia at a rate of 145
beats/min is supported by these observations. First,
this rate is one-half that of the underlying flutter rate
of 290 beats/min, with an identical p-wave
morphology and apparent vector. Second, each of the
rhythms (the typical flutter at a rate of 290 beats/min
and with exit block at a rate of 145 beats/min) occurred spontaneously with progression from one to the
other over several days with repeated documentation
and without any significant interval change in medical
therapy. Third, both spontaneously and with carotid
pressure at the atrial rate of 145 beats/min, highdegree AV block occurred without alteration of the
underlying atrial mechanism. This behavior is that
predicted for a flutter mechanism. It is particularly in-
FIGURE 2. Supraventricular tachycardia at a rate of
145-150 beats/min recorded 2 days after ECG in figure 1. Pwave morphology in lead V1 is identical to that in figure 1.
Diminutive p waves also appear in inferior leads. Progression back and forth from this pattern to the rhythm in figure
I was documented several times.
teresting to compare elements of this with the report
of Dressler et al.,6 in which they describe the association of PAT with exit block. In their patient, an intrinsic atrial rate of 300 beats/min was documented with
the spontaneous development of 2: 1 exit block in a
fashion similar to our case. Furthermore, their rhythm
strips show a p-wave morphology with peaked p waves
in V1 identical to those of our patient, suggesting a
similar site for an ectopic focus. They also point out
the difficulty in determining whether the underlying
rhythm in their patient was flutter or PAT. At times,
the baseline in their patient's ECG was isoelectric and
other times, it was clearly "sawtooth." We noted a
similar pattern in our patient (compare figs. 1 and 3).
The second interesting feature of this case is the
confusion introduced into the patient's management
by the repeated occurrence of the flutter mechanism
with exit block. Since control of her ventricular
response was critically important in her management,
digitalis had a major therapeutic role. Consequently,
ATRIAL FLUTTER/Homey et al.
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FIGURE 3. High-degree atrioventricular block recorded
during an episode of typical flutter with same p-wave
morphology. Atrial rate again is 290-300 beats/min.
with the rhythm disturbance noted above, PAT with
block reflecting possible digoxin toxicity was
repeatedly diagnosed. Although atrial tachysystole
with exit block has been associated with possible
digoxin toxicity,8 simultaneous digoxin levels in our
patient were relatively low (0.4-0.8 ng/ml on multiple
determinations) with normal electrolytes and, in particular, normal potassium levels. It was not until we
discovered the underlying mechanism for this rhythm
that a more appropriate approach to digoxin therapy
was initiated. In fact, control of the patient's rhythm
was finally achieved with ventricular pacing and
higher-dose digoxin therapy (0.375 mg/day), which
resulted in stable high-degree AV block. Previous
attempts to induce and maintain either sinus rhythm
or stable atrial fibrillation had been unsuccessful.
Although circus movement using specialized atrial
conduction pathways is thought to be the primary
..
713
mechanism for atrial flutter,11'12 the apparent development of exit block in atrial flutter lends support to the
hypothesis that an automatic pacemaker is an alternative mechanism in some patients. In addition to
older published work supporting this etiology (including vector analysis,"' simulated pacing studies,1
and atrial mapping2), Waldo et al.'3 have recently
demonstrated that it is possible to depolarize portions
of the atrium with surgically implanted wires during
spontaneous flutter. This supports the existence of
either an automatic focus or, alternatively, a small
reentrant loop that does not travel throughout the
atrium. The finding of flutter with exit block in this
patient is most consistent with either a discrete
automatic focus or possibly a small circumscribed
reentrant loop. This latter mechanism has been
suggested by the work of Allessie et al.,'7'8 in which a
small localized reentry process was demonstrated to
mimic a process of rapid impulse formation. Support
for an ectopic focus in our patient stems from the finding that the p-wave vector and in particular its
morphology in V1 is quite similar to that reported by
Mirowski and Alkan" to represent an underlying left
atrial automatic focus.
Our patient is well-controlled on higher-dose digoxin therapy with concomitant ventricular pacing. Both
our patient and that of Javier et al.5 eventually required v-demand pacing secondary to the development
of high-degree AV block with slow ventricular
responses. This unusual syndrome of atrial tachysystole with exit block may represent yet another
facet of the more general sick sinus syndrome. The
role that hypothyroidism might have played in leading
to this unusual form of exit block is difficult to
evaluate.
References
1. Mariott HJL: Armchair Arrhythmias. Oldsmar, Florida, Tampa Tracings, 1965, p 43
2. Lown B, Marcus F, Levine HD: Digitalis and atrial tachycardia
with block: a year's experience. N Engl J Med 260: 301, 1959
3. Coffman JD, Whipple GH: Atrial flutter as a manifestation of
digitalis toxicity. Circulation 2: 188, 1959
4. Agarwal BL, Agarwal BV, Agarwal RK, Kansal SC: Atrial
flutter. A rare manifestation of digitalis intoxication. Br Heart
J 34: 392, 1972
5. Javier RP, Narula OS, Samet P: Atrial tachysystole (flutter)
with apparent exit block. Circulation 40: 179, 1969
6. Phibbs B: Paroxysmal atrial tachycardia with block around the
ectopic pacemaker. Circulation 28: 949, 1963
7. Dressler W, Jonas S, Javier R: Paroxysmal atrial tachycardia
with exit block. Circulation 34: 752, 1966
8. Miller H: Paroxysmal atrial tachysystole with exit block. J
Electrocardiol 4: 80, 1971
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FIGURE 4. High-degree atrioventricular
block during episode of supraventricular
tachycardia with same p-wave morphology
noted above with atrial rate of 145-150
beats/min using a chest monitoring lead
similar to lead V,.
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CIRCULATION
9. Calvino JM, Azan L, and Catellanos A: Paroxysmal atrial
tachycardia with exit block. Am Heart J 54: 444, 1957
10. Camp PD, Scherf D: Frequenzverdoppelung bei paroxysmalen
tachykardion und vorhofsflattarn. Wien Arch F Med 25: 67,
1934
II. Pastelin G, Mendez R, Moe GK: Participation of atrial
specialized conduction pathways in atrial flutter. Circ Res 42:
386, 1978
12. Katz LN, Pick A: Current status of theories of mechanisms of
atrial tachycardias, flutter and fibrillation. Progr Cardiovasc
Dis 2: 650, 1960
13. Mirowski M, Alkan WJ: Left atrial impulse formation in atrial
flutter. Br Heart J 29: 299, 1967
14. Rosen KR, Law SH, Damato AN: Simulation of atrial flutter
VOL 60, No 3, SEPTEMBER 1979
by rapid coronary sinus pacing. Am Heart J 78: 635, 1969
15. Prinzmetal M, Corday E, Oblath RW, Kruger HE, Brill IC,
Fields J, Kennamer SR, Osborne JA, Smith LA, Sellers AL,
Flieg W, Finston E: Auricular flutter. Am J Med 11:410, 1951
16. Waldo AL, Maclean WAH, Karp RB, Kouchoukos NT, James
TN: Entrainment and interruption of atrial flutter with atrial
pacing: studies in man following open heart surgery. Circulation 56: 737, 1977
17. Allessie MA, Bonke FIM, Schopman FJG: Circus movement
in rabbit atrial muscle as a mechanism of tachyeardia. Circ Res
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in rabbit atrial muscle as a mechanism of tachycardia. Circ Res
39: 168, 1976
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Atrial flutter with exit block.
C J Homcy, B Lorell and P M Yurchak
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Circulation. 1979;60:711-714
doi: 10.1161/01.CIR.60.3.711
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