Download PAUL M. ZOLL, M.D. Invasive Temporary Pacing

PAUL M. ZOLL, M.D.
From the Department of Medicine, Harvard Medical School, and Beth'lsrael Hospital, Boston, Massachusetts
lOll PM: Noninvasive temporary cardiac pacing. External noninvasive temporary cardiac pacing has
beendevelopedas a feasibletechnique u1ith resolution of many of the earlier problems including th resholds
for pacing, cutaneousnerve pain, and skeletalmuscle contraction. At a stimulus duration of 40 msec, the
threshold for cardiac responseis reduced,u1hich significantly lou1ersthe extent and sev!rity of muscle
contractions. With experiencein thousands of patients, noninvasive temporary pacing has beenproven t(1
be botll safeand effective.(J Electrophysiol, Vol. 1, 1987)
atrioventricular block, bradycardia,cardiac arrest, hemodynamics,resuscitation, threshold
Electrical stimulation of the heart was introduced into clinical use in 19521as an externally applied, noninvasivemeans of resuscitating
the heart from ventricularasystoleor symptomatic bradycardia. Any procedure used in the
emergency of standstill or bradycardia must
permit quick and easyapplication, must bereliable, and must be safe.Noninvasivetemporary
cardiac pacing met these stringent requirements. This technique was widely used for
many yearsin emergencysituationsto stimulate
ventricular beats and to prevent ventricular
tachycardia and fibrillation by overdrive suppression.2--1
In nonemergencysituations, noninvasive pacemakers were often prepared in
standbyreadinesswhen impending arrestwas
feared.5
The large electric stimuli required for noninvasive cardiac stimulation usually produced
sharp burning or stinging pain in the skin and
strong contractions of skeletal muscles. This
discomfort, often intolerable,restrictedexternal
stimulation to use in unconscious patients or
to brief use in desperatesituations. In addition,
cardiac responses were often unrecognizable
becausethe large stimuli distorted the electro-
cardiograms and the muscular contractions
obscured arterial pulsations.
Cardiac stimulation was found to be ineffective during ventricular tachycardia or fibrillation. It is also ineffective in the presence of
severedepressionof myocardialexcitabilityand
contractility. 3 After prolonged arrest (four
minutes or more), stimulation is rarely lifesaving: usually it producesno cardiacresponse
at all; occasionallyit provokes brief episodes of
clinicallyuselesselectromechanicaldissociation.
Late in arrest that was caused initially by ventricular fibrillation, when the fibrillatory waves
havedied out and the electrocardiogramshows
a straight line, stimulation of the anoxic heart
is futile.
Many early papers reported successful resuscitation in unexpected arrest of varying
etiology.3Nonetheless, the many failures late
in arrest, together with the difficulty in recognizing cardiac responses,led to the erroneous
impression that external stimulation was effective only in Stokes-Adamsdisease(i.e., in the
presenceof high-degreeAVblock), or eventhat
external stimulation was not effective at all.
InvasiveTemporaryPacing
Address for conespondence: PaulM. ~1I. M.D.. Department
of Medicine. Beth Israel Hospital. 330Brookline Ave.. Boston.
MA 02215.
156
A substantiallydifferent, invasive, transthoracic technique for emergency cardiac pacing
was introduced in 1958." This technique, a
Journal of Electrophysiology
Vol. 1. No.2. 19R7
NONINVASIVE
TEMPORARY CARDIAC PACING
modification of the method developedby Albert
Hyman in 1932,7involved inserting a wire
electrodeinto the myocardiumvia a trocarpassed through the chestwall directlyinto the heart.
The procedure is hazardousand uncertain: the
heart and adjacent organs may be damaged,
and the myocardium may not be reached.R
Although successful resuscitation is infrequent,
the delays in application of this method make
meaningful evaluation difficult. 1t has never
been generally accepted, but it is still used at
times as a final, desperate measure.lI-tO
Introduced in 1958,11pervenous placement
by cardiaccatheterizationof an endocardialelectrode connected to an externalpulse generator
is an invasive method of temporary cardiac
stimulation. Subsequently, placement of the
pulse generator under the skin has provided
the most widely used technique of long-term
cardiac pacing. Becauseof the pain and supposed ineffectiveness of noninvasive pacing,
endocardial pacing was generally preferred,
even for temporary use, in both emergencyand
standby situations.
Invasive endocardial pacing has proved
unsatisfactory, however, for temporary cardiac
stimulation. Under the urgent and often hectic
circumstancesof cardiacarrest, placementof an
endocardial electrode is usually too difficult,
slow, and uncertain. It requires skilled personnel and considerable time, equipment, and
space, often interfering with other necessary
resuscitative procedures. In standby applications, the invasive procedure is an additional
burden often poorly tolerated by unstable
patients. The incidence of complicationsis high
(up to 34%).12.13
Consequently, the discomfort
and complications of the procedure must be
balanced against the estimated risk of arrest
every time catheterization is considered. Because of the likelihood of displacement of the
electrode and of infection, endocardialpacing
is usually stopped within five days.
Noninvasive Mechanical Pacing
In 1976,an external noninvasive mechanical
cardiac stimulator was introduced.14 When
applied to the precordium, this instrument
Vol. 1. No.2, 1987
provided mechanicalimpulses that stimulated
atrial or ventricular beats. It was used successfully in over 100 subjects, for the arousal or
accelerationof the heart in ventricular standstill
or bradycardia,for the termination of atrial and
ventricular tachycardias, and mostly for the
arousalof ectopic ventricular beats on demand
in noninvasive studies of postextrasystolic
potentiation.l~ Although better tolerated than
noninvasiveelectricstimulation, the mechanical
stimuli were usually too painful for prolonged
use, and the techniquewas finally abandoned.
Modified Noninvasive Temporary
Pacemaker-Monitor (NTP)*
In response to the difficulties with previous
noninvasive and invasive methods of cardiac
stimulation, a modified technique of external
noninvasive temporary electric cardiac pacing
was introduced in 1981.16.17
The effects of variations of the stimulus and of the electrodes on
the thresholds for cardiac response, for cutaneous sensory nerve pain, and for skeletal muscle
contraction were examined.16 Strength duration curves for stimulation of skeletal and
cardiac muscle were found to differ significantly
in that skeletal muscle is stimulated maximally
with electric pulses less than 1 msec long,
whereas the threshold for cardiac muscle continues to drop with pulses longer than 5 msec.
With stimuli of 40 msec, the threshold for
cardiac responses is reduced, usually to 35 to
70 mA. These low currents together with their
constant-current shape (relatively uniform
current amplitude without current spikes that
preferentially stimulate skeletal muscle) greatly
reduce the extent and severity of muscle
contractions.
The threshold for cutaneous nerve pain is a
function of current density (mA/cm2). The
threshold is not reached and the skin pain is
eliminated by using large electrodes with
nonmetallic inner surfaces that transmit the
stimuli of relatively low and uniform current
density across the skin without "hot spots" of
localized high intensity.
*Noninvasive Temporary Pacemaker.ZMI Corporation, Cambridge. MA.
Journal of Electrophysiology
157
ZOLL
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Figure 1. Electrocardiogmm showing nonnal sinus rhythm, i~
and ineffrctive stimuli (0) with return of nonnal sinus rhythm.
In addition, the NTP contains a specially
designedmonitor that provides full monitoring,
alarm, and demand functions. The monitor
controlsthe large,prolongedstimulus signalby
inactivating the amplifier circuitry for 80 msec
to preventsaturation.The monitor also presents
a clearly recognizable, unique symbol of the
stimulus artifact that precisely marks the time
of stimulation. These innovations promote
ready identification of both stimulated and
intrinsic beats (Fig. 1).
Safety of the Noninvasive Temporary
Pacemaker
Another prevalent misconception was that
stimuli longer than 5 msecincreasethe risk of
ventricular fibrillation. Since the NTP uses a
stimulus duration of 40 msec, the relation of
stimulus duration to the risk of producing
repetitive responses,tachycardia,or fibrillation
was examined in animals before the NTP was
applied to patients. With stimuli 5 to 100msec
long, the thresholds for repetitive responses,
tachycardia, or fibrillation were found to be 5
to 16times the thresholds for single responses.
Such high thresholds far exceedthe maximum
output of the clinical, modified noninvasive
pacemaker.16In a similar study in six normal
dogs,\borhees confinned theseresults,finding
the "safety factor" to average12.6,but neverto
be less than 7.18Thus, the NTP is incapable of
delivering a stimulus of sufficient amplitude to
provoke repetitive responses,tachycardia, or
fibrillation. Furthermore,for the sakeof comfort
158
"
~,
stimuli (0), effrctive stimuli (+) with ventricular CQpture,
in clinical situations, the stimulus amplitude is
adjusted to just abovepacing threshold for that
individual-again, far below the threshold for
fibrillation. In this regard, noninvasive pacing
is much saferthan invasive endocardial pacing
in which the pacing threshold may be so low
that the pulse generator routinely provides
stimuli well over five times the pacing threshold. Indeed, the placement of the endocardial
electrode itself carries a significant risk of
provoking ventricular fibrillation by mechanical
stimulation, even before pacing is started.
Oinical experiencewith noninvasive pacing
has confirmed its safety.No untoward cardiac
effectshave been documented since its introduction in 1952,even in the presence of competition between the artificial pacemakerand
intrinsic rhythm, or during acute myocardial
infarction. The NTP has now been used in
thousands of patients: clinical experience has
beenaccumulating,and many clinical trials are
being reported in varied clinical settings.19-22
As would be expectedin desperateclinical situations, ventricular tachycardia and fibrillation
have occasionally occurred. In only one instance,however, was tachycardia precipitated
by a stimulus: in a terminally ill patient with
recurrent ventricular tachycardia, a paroxysm
was delibenztely
provoked to evaluate a toxic,
antiarrhythmic drug regimen.19
In our large clinical study of the NTP,1911
patients who were undergoing either myocardial infarction or endocardial pacing suffered
ventricular tachycardia or fibrillation that required countershock. Noninvasive pacing was
Journal of Electrophysiology
Vol. 1, No.2, 1987
NONINVASIVE TEMPORARYCARDIAC PACING
Comfort and Effectiveness of Noninvasive
Temporary Pacing
.Effective stimulation signifies only the excitation. of a cardiac depolarization. Whether a
cardIaccontractionfollows dependson the state
o~ electro~echanical coupling in the myocardIum. StImulation with the NTP is usually
effective and usually comfortable or tolerable
for' most conscious subjects (about 90%) at
threshold levels between 40 and 70 mA.19
Thresholds as low as 20 mA have rarely been
observed, but levels up to and above the
maximum of 140 mA are often present when
cardiac excitability has beendepressed.Intolerable discomfort may also infrequently prevent
effective stimulation even at low levels,in some
instances from severe skin pain at the site of
small nicks or abrasions of the skin under the
electrodes. Intolerance, also caused by severe
apprehension, may be relieved by small intravenous doses of morphine, meperidine, or
diazepam, as is often done during cardiac
catheterization. Strong muscular contractions
may be tolerable for brief periods, but they may
become intolerable with prolonged or rapid
stimulation. Pulmonary emphysemaand large
pectoral muscles may lead to high thresholds
for stimulation and strong, painful contractions.
Obesity and large body size are not clearly
associated with high thresholds; on the other
hand, many frail patients with thin chestwalls
are comfortably stimulated at thresholds below
45mA.
Hemodynamic Responsesto Noninvasive
Temporary Pacing
Oinical observationsfrom 1952to the present
have demonstrated hemodynamically effective
responses to nonInvasive pacing in literally
thousands of subjects,with many resuscitations
from arrest and restorations of effectivecirculation. Comparisons of sequentially applied
endocardial and noninvasive temporary pacing
in 21 patients showed the hemodynamic
Vol. 1. No.2. 1987
responses to be similar.19A detailed hemodynamic study of 16patients who underwent
endocardialand then noninvasive pacing during cardiac catheterization again showed
equivalent hemodynamic responses to both
pacing techniques.23Incidentally, noninvasive
pacing initially stimulatesthe right ventricle, as
does right ventricular endocardialpacing. The
electricaland mechanicalresponsesof the heart
and, therefore, the hemodynamic and clinical
effectsof stimulation depend on the condition
of the heart and the circulatory system. The
effectsalso depend on the heart rate and atrioventricular sequence. They do not depend,
however, on whether pacing is endocardial or
external.
Clinical Application of Noninvasive
Temporary Pacing
The NTP has now beenapplied successfully
in all the conditionsfor which temporarypacing
has been used: in the emergency of asystolic
arrestor symptomaticbradycardia;in overdrive
suppressionor tennination of repetitiveventricular ectopy, tachycardia, and fibrillation; and
in standby readiness during periods of increased risk of arrest.
Asystole and bradycardia generally result
from depressionof the sinoatrial node or from
AVblock. Such depressionof rhythmicity and
conduction may be causedby many factors or
combinations of factors. Known conditions
include myocardial infarction. either acute or
old; sinus node dysfunction ("sick sinus syndrome"); reflex vagal depression from hypersensitivecarotidsinus or gastrointestinalreflexes
often associatedwith nauseaor vomiting (often
induced by drugs, particularlychemotherapyfor
malignancy); toxicity of cardioactivedrugs (digoxin, verapamil, quinidine, lidocaine, betablockingagents);hyperkalemia;countershockfor
atrial or ventricular fibrillation or tachycardia;
Stokes-Adams
disease;failureof long-termcardiac
pacemakers;proceduresto implant, revise, or
replace pacemakers;anesthesia,especially in
patientswith impairedrhythmicityor conduction;
and cardiac catheterization,angiography, and
angioplasty.
The specialfeaturesof noninvasive pacing -
Journal of Electrophysiology
159
ZOLL
its easy,quick, and safe application-make it
particularly valuable in emergency resuscitation. The successof emergency resuscitation
depends primarily on the duration of the an'est,
which in turn determinesthe amount of cardiac
and cerebral anoxia. The duration of arrest is
influenced by many parameters, which have
been carefully studied: location out-of-hospital
or in-hospital; witnessedor unwitnessedan'est;
location within the hospital; time of arrival of
personnel; initial attemptsat endocardialpacing
or intravenous drug therapy (atropine, sympathomimetic agents); state of consciousness;
and initial rhythm of bradycardia or asystole
alone, or fibrillation followed by asystole.
The same special features of the NTP make
it singularly valuable in situations of nonemergency pacing as well. When impending arrest
is expected, the NTP can be easily and safely
applied with relative comfort for prolonged
periods. The ordeal and risks of the surgical
procedure required to place an endocardial
catheterelectrodeare avoided. When expected
arrest did occur during the standby presence
of the noninvasive temporary pacemaker
monitor, resuscitationwas usually prompt and
successful,with survival of 23 of 26 patients in
our series.19In one patient, the NTP was
applied for an entire month during chemotherapy for malignancy becausehe suffered
nausea, vomiting, and resulting cardiac syncope in addition to bone marrow suppression
with leukopenia and thrombocytopenia that
contraindicated the invasive placement of an
endocardial electrode.
In addition to chemotherapyfor malignancy,
other contraindications to invasive placement
of an endocardialpacing electrodeincluded the
presenceof a tricuspid valve prosthesis,hemorrhagic states, digoxin toxicity with recurrent
ventricular tachycardia,and sepsis.Complications of endocardial pacing included failure to
install an effectiveendocardialelectrode,unreliability of an initially effective elect.r°.de.(probably due to displacement), precipitation of
ventricular fibrillation, and infection of an
electrode with septicemia.
Furthermore, the placement of a temporary
endocardial electrode-pacemakersystemwas
160
avoided in 57 patientsby use of the noninvasive
temporary pacemaker-a significant clinical
benefit. 19The easy,comfortable application of
the Nn' encouragedits use in unstable patients
with borderline indications. These patients
clearlybenefited from the extended protection.
Additional applications of the NTP are now
being tested that exploit the capability of safe,
comfortable, noninvasive, ventricular stimulation on demand in conscious patients. Rapid,
timed stimulation with specially designed
noninvasivepacemakershas beensuccessfulin
terminating atrial and ventricular tachycardias
in a few instances.24Tachycardia induced by
controlled noninvasive pacing has been used
successfully as a stress test in a series of 16
patients.23Unfortunately, the discomfort from
pectoral muscle contractions is increased with
rapid stimulation, so that about one-third of the
patients experienced significant discomfort.
Other applicationsinclude studies of postextrasystolicpotentiation, the effectsof cardiacdrugs
on the refractory period, and the suppression
of rhythmicity after tachycardia. These uses of
the noninvasive temporary cardiac pacemaker
require further exploration.
Thus, the NTP was developed as a logical
extensionof the original external cardiac pacemaker.It has solved the problems of severediscomfort and questionable effectiveness.It is a
safe,usually tolerable, and effective method of
ventricular stimulation. Being noninvasive, it
is quicker, easier,more certain, and safer than
endocardial stimulation. Therefore, it is the
method of choicefor current and future applications of temporary ventricular pacing.
References
1. Zoll PM: Resuscitation of heart in ventricular
standstill by external electrical stimulation. N EnE!
J Med 247:768,1952.
2. Zoll PM, Linenthal AI, Nonnan LR, et al: External
electric stimulation of the heart in cardiac arrest:
Stokes-Adams disease, reflex vagal standstill,
drug-induced standstill, and unexpected circulatory arrest. Arch, Intern Med 96:639, 1955.
3. Zoll PM, Linenthal AI, Norman LR, et al: Treatment of unexpected cardiac arrest by external
Journal of Electrophysiology
Vol. 1, No.2,
1987
NONINVASIVE TEMPORARYCARDIAC PAONG
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Nicholson MJ, Eversole VE, Orr RB, et al: A
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Thevenet A, Hodges PC, Lillehei CW: Use of a
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Brown CG, Gurley HT, Hutchins GM, et al:
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