- Email: [email protected]
Effect of caffeine on the ventricular fibrillation threshold in normal dogs and dogs with acute myocardial infarction
Effect of caffeine on the ventricular fibrillation threshold in normal dogs and dogs with acute myocardial infarction Samuel Bellet, M.D.” Eckhurd Horstmann, M.D.** La&an R. Roman, M.D.*** Norberto T. DeGuzmnn, M.D.*“** John B. Kostis, M.D.***** Philadelphia, Pa.
R
ecently, our laboratory as well as others has been interested in studying the various stress effects of caffeine such as the elevation of plasma adrenocortical steroid concentrations, blood free fatty acid levels, and adrenergic effects.‘es In addition, caffeine may increase the concentration of cyclic adenosine monophosphate (AMP) by competitive inhibition of phosphodiesterase and may decrease the binding of Ca++ by the cell membrane.gj10 Because some of these pharmacologic effects are known to induce ventricular fibrillation,11~‘3 it would be of interest to study the effect of caffeine on the ventricular fibrillation threshold (VFT), The aim of the present work was to study the effect of caffeine on the VFT in normal dogs and in dogs with experimentally-
induced myocardial infarction during the acute stage of the occlusion. In order to evaluate the relation of the changes in VFT after the administration of caffeine to the adrenergic effects, experiments were also performed after pretreatment with propranolol and with practolol. Methods
and
materials
Mongrel dogs weighing 25 to 30 pounds were anesthetized intravenously with sodium pentobarbital, 25 mg. per kilogram of body weight. Respiration with room air was maintained by means of a Harvard ventilatory pump through an endotracheal tube. Tidal volume and respiratory rate were set according to the weight of the animal, utilizing the ventilatory graph prepared by Kleinman and Radford. Arterial
From the Division of Cardiology, Philadelphia General Hospital, Philadelphia. Pa. This work was aided by Grant No. 71-589-l from the Commonwealth of Pennsylvania and by the Foundation for Cardiovascular Research, Philadelphia, Pa. Received for publication Oct. 15, 1971. Reprint requests to: Samuel Bellet, M.D., 2021 Spruce St., Philadelphia, Pa. 19103. *Director, Division of Cardiology, Philadelphia General Hospital; Professor of Clinical Cardiology, Graduate School of Medicine of the University of Pennsylvania; and Lecturer in Pharmacology, University of Pennsylvania SchOol of Medicine. **Cardiology Chief Resident, Division of Cardiology, Philadelphia General Hospital. ***Cardiologist, Division of Cardiology, Philadelphia General Hospital. ***Research Fellow, Division of Cardiology, Philadelphia General Hospital. *****Research Associate, Division of Cardiology. Philadelphia General Hospital.
l,‘ul.
N, No.
2, pp. 21522i
August,
1972
American Heart Journal
215
III
Ipig. 1. Determilution of the ventricular fibrillation threshold (VFT) by delivering (G) through previously implanted epicardial electrodes. S, pacemaker stimulus; F, ventricular fibrillation. Note the progressive increase of the amplitude of the gated
pH, E’co~, and Pas were monitored by the use of a radiometer. The values did not show significant deviation from the normal. The temperature was recorded every 15 minutes by means of a rectal thermometer. The electrocardiogram (ECG) was monitored through an oscilloscope and recorded each time the VFT was measured with a Sanborn Viso-100 recorder at a paper speed of 50 mm. per second. The blood pressure was measured by means of a catheter inserted in the descending aorta
gated series of impulses R, vwtricular complex; impulse (G’) from I to III.
3
utilizing Statham 23Bd transducers and Electronics-for-Medicine amplifiers. Two groups of experiments were performed. In the first group the ventricular fibrillation threshold (VFT) was determined in intact dogs by delivering electrical impulses through the chest ~vall. In the second group the impulses were delivered directly to the heart through previousI)’ implanted epicardial electrodes. These electrodes were attached to insulated wires wl~ich were exteriorized through the chest
7’uOl~~
i. j;)O;d
of
sorlirtm
bcn~otrfc
on
the
ventricular~fibrillation
Minules
after
~--~__-_-~Ihg 0 I. 2. , :; : .5 . (I. 7.
-
I
15
0. sot 0.45 0.45 0.35 0. 70 0.50
0.50 0.45 0.40 0.35 0. 70 0.50 0. 70 0. 60 0.30 0.40
0.70 0.60 0.30 0.45
h. 0. II). .~-
I
(llliil.)
intact
yzormul
dogs*
injection
45
30
in
I
0.50 0.45 0.40 0.35 0.70 0.50 0.75 0.60 0.20 0.45
60
90
0.55 0.45 0.40 0.40 0.70 0.50 0.75 0.45 0.20 0.55
0.50 0.45 0.40 0.35 0. 70 0.50 0.75 0.45 0.25 0.55
Mean diflerence
No. qf dogs
0
10
15
10
30
10
45
10 10 10
60 90
intravenous ~_~_____
0.45 0.50 0.40 0.40 0.70 0.45 0.70 0.60 0.30 0.45
I The after clrztg admin.
threskold
Mean VFT (mutt-sec.)
0.50 0.49 0.495 0.49
0.495 0.49
*Dosage 12.5 mg. per kilogram of body iVFT in watt-seconds. $Differences not statistically significant
jrom
0 lime value (watt-sec.)
VlViCkllU
S.E. M.
0.01 0.005 0.01
0.0444 0.00136 0.00155
0.067 0.011 0.012
0.005
0.0058 0.0043
0.024 0.02
0.01
t
I’
0.149 0.454
N.S.$ N.S.
0.833 0.208 0.50
N.S. N.S. N.S.
wei::ht. at the 5 O,b 1~x1
on the basis
wall and were thus available for stimulalion. GYOZI~IA. In the first group (Group A, intact dogs), a method similar to that described by Lou-n, Kleiger, and Williams13 was utilized. Caffeine and control experiments were performed on normal dogs and on dogs with acute myocardial infarction. Tile method is briefly as follows. Two electrode paddles measuring 8?4 cm. in di;ulleter covered with conductive paste were q~plied with pressure externally on both sides of the shaved chest at the level of the apical thrust. These paddles were held in a fixed position with rubber straps across the chest. Electrical discharges were delivered utilizillg tlie Idown Cardioverlrr RIodel 10530-H \\,itll ;t 16 nlicrofarad crrpac.itor ~ltrough 3 100 millihenry inductor. A voltage-dividing network was connected in series with the electrodes in order to obtain
of a pailed
corn~~arison.
accurate measurement of the discharge ;~t the range of 0- to 10 wsec. [watt-seconds) at increments of 0.05 wsec. The fibrillation threshold was determined by sweeping the Q-T interval of the cardiac cycle with stimuli of increasing energy from subthreshold to threshold levels. This was performed by progressively increasing the delay of the stimulus from the peak of the R wave by increments of 10 milliseconds using a 15 to 20 second interstimulus interval. The criterion of the VFT was tile minimal energy producing ventricular fibrillation for at least 10 seconds. The presence of ventricular fibrillation was established by tlie I<(‘(; and the disappearance of pulsatile aorlic: 1)ressure (I;ig. 1). Collll1.ersl~ocks\\,i 111energy ranging frunl SO to 2~) wsec. \vc’re applied in order to convcrl ventricular fibrillation to normal sinus rhythm. After an episode of ventricular
lirl~e
II. Efect
of cufeine
sodium
benzoute
on ventricz{lurJiDrilllltion
threshold
in iduct
normd
dOgS*
1. 2.
0.651 0.50
0.50 0.50
4: 3 5. 0. 7. 8. 9. 10. 11.
0.50 0.40 0.50 0 4.5 0.50 0.55 0.35 0.70
0.50 0.40 0.40 0.45 0.45 0.45 0.55 0.30 0.70
----
0.55 0.35 0.40 0.35 0.35 0.40 0.50 0.35 0.50 0.30 0.60
_______ ~~______
.~-__
0.50 0.30 0.40 0.35 0.30 0.35 0.40 0.30 0.40 0.30 0.60 .-....
0.55 0.30 0.45 0.35 0.35 0.25 0.35 0.30 0.30 0.25 0.50
0.40 0.35 0.45 0.35 0.35 0.35 0.35 0.40 0.40 0.25 0.55 ___--~-
--~
~
Mean Time after admin. of cizffeeine (min.)
0 1.5 30 4.5 60 90
_
difference
No. of dogs
Mean VFT (watt-sec.)
11 11 11 11 11 11
0.509 0.473 0.423 0.382 0.359 0.382
*Dosage 25 mg. per kilogram tVFT in watt-seconds.
of body
from
0 time value (watt-sec.)
0.036 0.086 0.127 0.150 0.127
Variance
S.E.lf.
0.002546 0.001307 0.002682 0.005500 0.003182
0.0152 0.0110 0.0120 0.0224 0.0170
t
3.368 7.818 10.580 6.696 7.470
’
P
0.05 0.001 0.001 0.001 0.001
weight.
fibrillation, a period of at least 10 minutes was allowed before a new series of stimuli were applied. The ventricular fibrillation threshold (VFT) jvas determined in 11 normal dogs at 1.5 minute intervals before and for a period of 90 minutes after intravenous injection of 25 mg. per kilogram of body weight caffeine sodium benzoate (corresponding to 12.5 mg. per kilogram of body weight caffeine base). Control experiments, of the same duration in which sodiunl benzoate (12.5 mg. per kilogram of body weight) was injected, were performed in 11 other dogs. Similar studies wcrc pcrforlned ;Jso in dogs during tlie acute phase of Ilt)*ocardial infarction produced I)y t\\o-stage ligation of the anterior descending artery.‘4 Tile
experiments mere performed on the fourth day after coronary ligation because in an earlier stage the presence of frequent prcmature ventricular contractions interferes with the proper determination of the VFT. Caffeine experiments were performed in 11 dogs with acute infarction, whereas control experiments were performed in 6 such dogs. In addition, similar experiments were performed on 9 normal animals treated 1)~ a combination of caffeine sodium benzoatc (25 mg. per kilogram of body weight) and propranolol (0.2 mg. per kilogram of 1)ody weight). Five other animals were treated \vith intravenous injections of propranolol (0.2 n1g. ])c:I- kilogr;ml (of Iwd)~ \\.cigllt) ;IlOW. C;rozc,b f3. In tile second group of experiments (( ;roup 13, dogs with pre\iously itrl-
‘I’trblt: III. Effect of so&m bipolar ,implanted electrodes
benzoate on the ventricular jibridlafion threshold in nomad dogs with (third to seventh day after implantation)* Minutes
1. I ;: 1. .i. 0. 7. 8. 0. 10.
after
intravenous
injection
14t
16
14
16
16
16
15
18 16 16 12 10 9 17 12 12
17 15 18 11 0 11 1Y 11 12
18 13 18 11 10 10 20 11 12
18 16 16 13 10 10 18 11 13
15 19 15 13 9 10 19 12 9
1.5 19 18 11 10 11 19 12 12
13 I6 12 10 0 18 10 14
t
P
.__.~ Time after admin. of sodium benrnate (min.)
0 15 30 45 60 90 110
NO. of dogs
Mean VFT (Ma.)
10 10 10 10 10 10
13.6 13.9 13.7 14.1 13.7 14.3 13.0
Mean difference from 0 time oalue (Ma.)
I Vaariunce
S.E.M.
1
0.3 0.1 $0.5
2.233
0.47
0.64
0.7222
0.269
1.859
+::: -0.3
1.555 2.4444
0.394 0.494
1.776 0.668
N.S.~ N.S. N.S. N.S. N.S. N.S.
*Dosage 12.5 nx. per kilograni of body weight. IVFT in milliamperes. :Differences not statistically significant.
planted electrodes), electrical discharges were delivrered directly to the myocardium Iq means of specifically constructed bipolar epicardial electrodes implanted on the right ventricle three to seven days prior to the experiment. These electrodes consist of two stainless steel wires, 1 mm. in diameter, embedded 10 mm. apart in a small acrylic plaque. They were connected to Tefloncoated treated silver lvires which were exteriorized through the chest wall. The heart rate \vas kept constant during each experinient 1)~ pacing the right atrium at a rate above the spontaneous rate of the animal by means of a similar pair of implanted elec~trotl~5. An American Elwtronics Lalb w;~s rrtilized for this orator\~ stiiilulator impulse \vas douplll-~)OStZ!.Tire pacennkr I,le the pacing tliresliold in intensity and
VFT
Contrai ,“ormall
05
Wa’t’sec. :;I!%, I5
30
45 Ttme (mini
i--Id
60
75
90
Fig. 2. ‘The effect of caffeine on the VF’T of normal dogs and dogs with acute myocardial infarction (impulses delivered through the chest wall). No change in the normal rontrols. 1;oIlowing caffeine drni~~ihtralion, the \‘l;‘I‘ drops. ‘I’he colrll-ol value< of dogs with acute mpcardial infarctirm (.A All) de lower than Iumrtl. b’urther tlet~.~~ is oljherved after caffeine.
220
Am. Heart 1. August. 1972
Bellid et ul.
l’uhle IV. l’he qfects of cclfleiae sodium bensoute on the T/F1 fAuntcd c~lrctrodcs (third to seventh duy after implantation)*
in normtrl
dogs with
lzipolllr
im-
Minutes after intrave~zous injection
Mean
Tinze after adnzin. of caffeine (min.)
0 15 30 45 60 90 120
No. of dogs
Mean VFT (Ma.1
10 10 10 10 10 10 10
14.6 11.6 9.2 9.6 10.9 13.5 14.2
*Dosage 0.25mg. per kilogram of body tVFT in milliamperes. tIXfferences not statistically significant.
difference from 0 time value (Ma.)
3.0 5.4 5.0 3.7 1.1 0.4
Varariance
12.8888 6.2800 6.0000 6.6777 6.5444
S.E. M.
1.135 0.836 0.775 0.817 0.809
t
P
2.643 6.459 6.452 4.529 1.360
0.05 0.001 0.001 0.01 N.S.# N.S.
weight.
2.5 msec. in duration. The VFT was determined by delivering gated impulses to the right ventricle through the previously implanted bipolar electrodes utilizing a method similar to that of Han.15 These impluses were programmed using a series of Tektronix waveform and pulse generators which trigger a Grass stimulator (model SDS). At every tenth heart beat, this system delivers a series of rectangular pulses of 2.5 msec. duration each at intervals of 10 msec. The series of impulses starts immediately after the R wave and ends at the peak of the T wave, adequately covering the vulnerable period. The cllrrent inrr-eased at increnients of 1 l\la. ulitil veil-. tricular fibrillation \vas observed (Fig. 1). The current delivered to the dog was measured with a current probe amplifier
and displayed on an oscilloscope. Ten control and 10 caffeine experiments were performed on normal dogs. In addition, 5 experiments were done on animals treated by the combination of caffeine sodium benzoate (25 mg. per kilogram of body weight) and practolol (0.6 mg. per kilogram of body weight). Results Control and caffeine experiments 016 IIOYrnul dogs. In Group A (intact dogs), no change in the VFT was noted during the 90 minutes following the injection of sodium benzoale. In conLrast, after injection of caffeine sodium I)enzoate a significant decrease in the fibrillation threshold was noted at 1.5, 30, 45, 60, and 90 minutes after the injection. The maximum effect
l’rllde V. fib/h of sodium htsoutc on the ventriculur myoccudicil 2nfWction (foltrth postoperc~tivc day)* Minutes __-
--__-
after
$/X&ion
intrave?tous
threshold in dogs with clctdte
injection ____
Dog
1. 2. .3 . 4. 5. 6. 7. 8. 9. 10.
0
15
0.50t 0.50 0.45 0.40 0.35 0.20 0.30 0.50 0.45 0.25
0.45 0.55 0.45 0.45 0.35 0.20 0.30 0.45 0.45 0.25
30
I
I
0.45 0.55 0.40 0.45 0.35 0.20 0.30 0.45 0.40 0.25
45
/
0.45 0.55 0.40 0.45 0.45 0.20 0.30 0.45 0.40 0.25
60
90
0.45 0.55 0.45 0.40 0.30 0.20 0.30 0.45 0.45 0.30
0.50 0.50 0.45 0.35 0.30 0.20 0.30 0.50 0.45 0.30
I_-
__-_
Time after drug admin. (min.)
0 15 30 45 60 90
No. of dogs
Mean VFT (watt-sec.)
10 10 10 10 10 10
0.39 0.39 0.38 0.39 0.385 0.385
*Dosage 12.5 mg. per kilogram of body tVliT in watt-seconds. tlXfferences not statistically significant
Mean difference jronz 0 t&e value
0 0.01 0 0.005 0.005
Variance
S.E.M.
0.00155
0.012
0.00136 0.00081
0.011 0.009
t
0 0.833 0 0.45 0.55
P
N.S.t. N.S. N.S. N.S. N.S.
weight. at the 5yo level
on the basis
\\XS noted at about 45 and 60 minutes, when the mean VFT decreased to 0.382 and 0.359 wsec. from a control value of 0.509 wsec. (P < 0.001) (see Tables I and 11, and Fig. 2). Similar results were observed in Group B (normal dogs with previously implanted epicardial electrodes) (see Tables III and IV, and Fig. 3). There was a statistically significant decrease in ventricular fibrillation threshold at 15, 30, 45, and 60 minutes with a maximum effect at about 45 and 30 minutes (9.6 and 9.2 respectively, from a control value of 14.6 Ma., p < 0.001). There was no change in the control experiments (i.e., after the injection of sodium benzoate). Dogs with experimental myocardial infarction (caffeine and control experiments.). The results obtained in this group of dogs are
of a paired
comparison.
nh,
Fig. 3. The effect of caffeine on the VFT of normal dogs (impulses delivered through previously implanted epicardial electrodes). There is a decrease in VFT after caffeine administration while there is no change in the controls and in those treated with the combination of caffeine and practolol.
_____ I
_____--_I__
Peg
1. 2. 3. 4. .5 . 6. 7. 8. 9. 10. 11.
0
15
0.4ot 0.25 0.50 0.40 0.30 0.40 0.60 0 ,40 0.35 0.30 0.60
0.30 0.20 0.35 0.35 0.25 0.35 0.60 0.40 0.35 0.25 0.60
_-_I------.-_____-----~~ 30
I
.---I
I
45
60
0.25 0.30 0.30 0.30 0.20 0.35 0.55 0.45 0.30 0.30 0.35
0. ‘0 0.30 0.30 0.25 0.20 0.30 0.60 0.45 0.35 0.35 0.35
~-.
-.
(/f>
I 0.25 0.25 0. 30 0.30 0.25 0.35 0.60 0.40 0.30 0.30 0.10
0.30 0.30 0.30 0.35 0, to 0.35 0.55 0 .4.5 0.35 0.35 0. 3.T
--_-__--
Time
Xean diference
after
admin.
of
cafe&e (min.)
0 1.5 30 4.5 60 90
No. of dogs
11 11 11 11 11 11
Mean VFT (watt-sec.)
0.409 0.364 0.327 0.323 0.314 0.332
from 0 time
-0.045 -0.082 -0.086 -0.095 -0.077
given in Tables 1: and \iI and in Fig. 2. 111the control experiments, no significant cllange in the VF’I‘ occurred, whereas after caffeine administration the VI!?’ was significantly decreased at 15, 30, 45, 60, and 90 minutes (p < 0.01). The maximum effect was noted at 45 and at 60 minutes \vhen the mean VFT decreased to 0.323 and 0.314 Ivsec., respectively, from a control value of 0.409 wsec. As expected, the VFT before the injection of caffeine (0.409 jvsec.) was lower in dogs with acute myocardial infarction than in normal dogs (0.509 wsec.). Administration
of
the
Vuriance
S.E. Al.
0.002227.5 0.00464 U.OO7046 0.009228 0.008182
0.0142 0.0206 0.0253 0.0289 0.0273
t
i
I’
value (watt-sec.)
conzbinations
of
cclzeine und $wopranolol and cafe&e and practolol. As seen in Table VII, propranolol in the dose of 0.2 mg. per kilogram of bodl Lveight did not significantly affect the VFT. However, lvhen administered simultaneously with caffeine, it prevented the caffeine-induced decrease in VFT. This is
3.169 3.981 3.399 3.287 2.825
show71in ‘I’al~le \.I II, where no clinngc in VFT is ol)served after the ~tdnlirlistratiorI of the propranolol-caffeine combinatiofl (Fig. 4). Similarly, no change in YE-T \t’;ls observed in the dogs treated with caffeincb and practolol (Table IX). Discussion 1. Til1lle.s
of ventriclllar
Jibrillation
thresh-
oZd. The values of VFT obtained in Group A (intact dogs) are in the range reported by Lawn, Kleiger, and Williams13 who employed a similar method. Those obtained in Group B (dogs with previously irnplanted electrodes) were similar to the results of Han,15 who utilized a similar technique. There w-asno change in the VFT in the control experiments. Prolonged anesthesia and repeated determinations did not significantly affect the VFT in the control experiments. This has been reported 1)y
Minutes
1. 2. 3. 1. 5. ~- _____-
0. 70t 0.50 0.35 0.80 0.35
0.70 0.50 0.35 0 80 0 35
before
(-)
0.80 0.50 0.35 0.80 0.35
and after
(+)
intrmenous
0.80 0.40 0.35 0.70 (1.35
injection
0.70 0.50 0.35 0.90 0.10
0.60 0.50 0.35 0.80 0.35
0.60 0.40 0.35 0.90 0.30
I_--
Meun T’FT (ml&ser.)
Xenn di$erenre jrorn 0 time control (wnlt-sec.)
others.1”~‘7 Although some variation in the control values of \‘FT between the groups of experiments was observed, these differences are not Statistically significant. ‘1 -. The efect of ccl$eine on the I’FT of noumciZ dogs. In contrast to the control experiments, caffeine produced a significant decrease in the \‘FT n:hich lasted at least 60 minutes. It is of interest that similar results were obtained with both techniques (Ciroups A and B). This is important, since the accurate determination of VFT is relatively difficult as it is affected by many variables and each technique is characterized by specific advantages and disadvantages.r8-?r The closed-chest technique, with impulses delivered through the chest wall of the intact animal, involves the problem of the chest wall impedance which might vary from dog to dog or from moment to moment on the same dog, but this technique does offer the advantage of using intact animals without previous operations. On the other hand, the technique utilizing implanted electrodes bypasses the problem
0
Fig. 1.
I5
The effect induced decrease of there is no decrease of the combination
30
45 Time
60
75
so
(men)
of propranolol on the caffeineVFT in normal dogs. Note that in VFT after the administration of caffeine and propranolol.
of variable impedance as well as the openchest problem, but introduces the factor of clot formation, electrode implantation, or myocardial reaction around the implanted electrode. Open-chest techniques were avoided in this study since they introduce important physiological alterations. 3. Eflect of caffeine on the b’FT of dogs
6. 7.
8. 9.
0.30t
0.30
0.45 0.30 0.75 0.80 0.70 0.60 0.40 0.35
0.15
0.35 0.45 0.25 0.70 0.80 0.70 0.60 0.30 0.40
0.50 0.30 0.75 0.80 0.60 0.60 0.40 0.40
0.35 0.45 0.30 0.75 0.80 0.60 0.60 0.40 0.40
0. hO 0.60 0.4) 0.40
l’oria~ce
S. E. ‘II.
t
I’
0.00382
0.0205
1.356
0.35 0.45 0.30 0.75 0.80 0.80 0.70 0.30 0.40
0.30 0.70 0.80 0.70 0.60 0.40 0.35
0.35
0.3.5
0.45 0.30 0.75 0.80
Mean Time after drug admin.
(mk)
No. of dogs
Mean
VFT
(watt-sec.)
difference front 0 tinre control (watt-sec.)
0
15 30 45 60 90
9 9 9 9 9
0.511 0.539 0.506 0.506 0.516 0.516
SO.028 0.005 0.00s 0.005 0.005
*Dosage caffeine sodium benzoate = 25 mg. per kilogram tVFT in watt-seconds. iD,ffI erences not statistically significant.
of body
with acute myocardial infarction. The VFT of dogs with acute myocardial infarction was lower than that of normal dogs. During the fourth day after coronary ligation, the heart muscle manifests the characteristic pathology of acute myocardial infarction and one would anticipate that the VFT would be below normal. These results are in agreement with observations of others who observed significant decrease in the VFT in ischemic hearts.15J2*23In dogs with acute myocardial infarction, the VFT which had been lowered because of ischemia was further decreased by caffeine. This might conceivably facilitate the development of spontaneous ventricular fibrillation (and sudden death) when myocardial ischemia and caffeine are operating simultaneously. 4. The efect of the combination of cafe&e and beta blocking agents on the VFT. As has been reported by others, propranolol (0.2
weight;
dosage
~~royranolol
= 0.2 mg. per kilogram
N.S.f N.S. N.S. N.S. 1N.S.
01 body
wcigl~t,
mg. per kilogram of body weight) did not affect the VFT to any significant degree.“4 However, propranolol probably prevented the caffeine-induced decrease in VFT whcu administered simultaneously with it. This effect is related to the beta-blocking actiou of propranolol rather than to its “quinidine-like” effect, since similar results were obtained by the use of practolol and “pure” beta-blocking agents which do not have significant direct action on the cardiac muscle. The dogs receiving this combination behaved similarly to the controls. These results would suggest that the effect on the fibrillation threshold may be mediated directly or indirectly through the adrenergic mechanism. It has been shown that sympathetic nerve stimulation results in an accentuation of asynchrony of recovery of the myocardial excitability leading to a marked decrease in VFT. Exogeneous catecholamine administration has the same
T&e IX. Effect of the combkation of caffeine sodium benzoate plus practolol on the ventricular fibrillation threshold in normnl dogs with bipolar implanted electrodes (third to seventh duy clfter implant&ion) * Minutes
after
30
1
i&ravenous
injection
Dog 0
/
15
1
45
1
60
/
90
/
120
-
1. 2. 3. 4. 5.
l‘inle after drug admin. (min.)
No. of dogs
Mean VFT (Ma.)
0 15 30 45 60 90 120
5 5 5 5 5 5 5
10.4 10.2 10.6 10.6 10.0 10.0 10.4
Mean difference from 0 time value (Ma.)
0.2 0.2 0.2 0.4 0.4 0.0
Variance
S.E.M.
0.70 1.70 2.20 1.30 1.30
0.38 0.59 0.67 0.51 0.51
*Dosape caffeine sodium benzoate = 25 mg. per kilogram of body weight; dosage practolol tVFT in milliamperes. IDifferences not statistically significant at the 5 % level on the basis of a paired comparison.
effect in the initial 5 to 10 minutes after administration.l’~25 Since caffeine results in stimulation of adrenergic activity,5v6 it may decrease the VFT through this mechanism. 5. Mechanism of decrease of VFT by ccL$eine. Caffeine has many pharmacologic effects which might be anticipated to affect the VFT. These include adrenergic stimulation, direct myocardial stimulation with increases in cardiac output, contractility, cardiac work, oxygen uptake, and coronary A-V difference. Agents, such as catecholamines and digitalis,n,25z26 producing similar effects are usually associated with depression of the VFT. A mechanism by which caffeine decreases the VFT is the adrenergic stim~ll;ltion Liorl of
rllwliouetl
ahove.
The
pre\w-
tile c~;~ffeiIlr-i~lduc-~(l dtxcreasr in \‘l;‘l‘ 114’ ~~~~pr;molul or practolol supports (Ilk view. ‘I’lle elevation of serum free fatty acid levels after caffeine administration rnny coutribute to this effect.‘a2 A rela-
0.53 0.33 0.30 0.78 0.78
= 0.6 trig. per kilogram
N.S.f N.S. N.S. N.S. N.S. N.S. of body
weight.
tion between serum free fatty acids and arrhythmias and death after acute myocardial infarction has been reported by a group of investigators. In addition, caffeine increases intracellular 3’,5’-cyclic AMP by inhibiting phosphodiesterase, elevatesserum adrenal steroid levels, and probably directly affects the action potential.1°J7 The factors mentioned above, singly or collectively, could result in facilitating the development of re-entry which under certain conditions might lead to ventricular fibrillation. The effect of caffeine on calcium may also play a role. Caffeine decreases the calcium binding which may lead to an increased concentration of calcium in the cell.9 Calcium was found to cause a reduclion in the maximum rate of rise of the xtion potential, which can slow tile \,ttlociLy of impulse propagation and shortens the refractory period. These effects would favor the development and maintenance of re-entrant excitation and possibly
226
Bellet et (11.
fibrillation.2* cium may
Irnder centain conditions calinitiate \Tentricular fihillation.‘”
Summary The effect of caffeine administration on the \TFT was studied in normal dogs and in dogs \vith acute myocardial infarction. TWO methods \vere employed; the first utilized impulses delivered through the chest wall of the intact animal and the second used epicardial electrodes implanted four to se\.en days previously. Caffeine produced a decrease in \.‘E’T starting 1.5 minutes after injection and tllis effect lasted about 60 minutes. I’ropranolol and practolol prevented tile caffeine-induced decrease of VFT. In dogs with acute myocardial infarction the \,-I!‘~ \\-a~ lo\i:er than normal and was further decreased after caffeine administration. Although the dose of caffeine utilized in this study is higher than that usually consumed by humans, it is possible that lower doses have a significant effect when combined with other agents. The various factors that affect the VFT w+ich might have arrhythmogenic effects are presently under study. There is suggestive evidence that a number of factors might be cumulatively significant in susceptible individuals. These factors may include cigarette smoking, various degrees of stress effects due to anxiety and exertion, various drugs--i.e., isoproterenol, ephedrine, and several sympathomimetic agents, and caffeine. The role of caffeine requires further study in this regard. REFERENCES 1.
2.
3.
4.
5.
Bellet, S., Kershbaum, .%., and Aspe, J.: The effect of caffeine on free fatty acids, Arch. Intern. Med. 116:750, 1965. Bellet, S., Kershbaum, A., and Fin&, E. M.: Response of free fatty acids to coffee and caffeine, Metabolism 17:702, 1968. Bellet, S., Kostis, J. B., Roman, I,., and UeCnstro, 0.: Effect of coffee ingestion 011 adrenocortical secretion in young men and dogs, Metabolism X3:1,007, 1969. DeSchaepdryver, A. F.: Physiopharmarological effects on suprarenal secretion of adrenaline and noradrenaline in dogs, Arch. I II~. I’h;lrm:~ctdy~i. ‘I‘hcr. 119:517, 19.50. Levi, I..: The effect of c,offee on the funcl ion of the s?nll)~~~l~o-adreno-lnedltll~~ry syste111 in mnu,
Acta bled. Srand. 181:431, 1967. Bellet, S., Roman, L., DeCastro, I)., Kitn, Ii. E., and Kershbaum, A.: Effect of coffee ilrgestion 011 catecholnmine release, Metabolism 18:288, 1969. ;\., Khorsandian, I:., Cal)l;~~l, 7. Kershbaum, R. E‘., Rellet, S., and Weinberg, I..: The role of c;~tccholnmines in the free fatty acid respouze to cigarette smoking. Circulation 28:.52, 196.1. A., Bellet, S., Jimellez, J.. :LII~ 8. Kershballm, Feinberg, I,. J.: Difference in effects of cigar and cigarette smoking on free fatty acid mobilizatiotl and catecholamine excretioll, J.A.M.:1. 195:1095, 1966. A., and Grollman. 1;. I;.: I’harnl,l0. Grollman, cology and therapeutics. 7th ed., I.ea & Febi~er. I’hiladelphia, 1970, p, 201. IO. Sutherland, E. \\~., Kobison, G. A., :llld Butcher. Ii. \Y.: Some aspects of the biolopical role (11 adenosille 3’.5’ monophosl)hate (cyclic ,111 I’), Circulation X:279, 1968. J., deJalon, I’. G., and kloe, G. K.: 11. Han, Adrencrgic effects on ventricular vulnerability, Circ. Kcs. 14:.516, 1964. l.., Howard, S. \I:., and Merrill, 12. Grumbarh, L.. I.: 1;artvrs related to the initiation of veiltricul;u fibrillation in the isolated heart. Efiect of calcium and I,otassium, Circ. Kes. 2:452. 1954. Ii., and \Villiams, J.: Cardio13. I,uwn, B., Kleiger, version and digitalis drucs: Chanced threshold to electric shock in digitnlized animals, Circ. Res. 17:519, 1965. A1. S.: I)elayed development of ven14. Harris, tricular cctopir rhythms following experimental coronary occlusion, Circulation 2:1318, 19.50. vulnerability during acute 15. Han, J.: \,Yentricular roronarqocclusion, ,\nl. J. Cardiol. 24:857, 1969. II. I)., Starmer, F., and \\‘halcn, 16. 1Irlntosh, Ii. E.: A comparison of the electrical ventriclllar librillation threshold with and without nnesthe&. .-\M. HEART J. 72:419, 1966. M.: Bretvlium tosylate for suppression 17. Fktcaner, of induced ventkcular tibrillation, Xm. J. Cardial. 17:528, 1966. C. Xl., Levy, I.. M., and b’Iacl.e;ul, 18. Phibbs, I*. I).: The influence of temperature and corenary occlllsion on the ventricular fibrillation threshold, Surg. Gynecol. Obstet. 109:216, 1959. 19. \~anTyr~. Ii. i\., and -\lacl,ean. I*. I).: YentrictlIar librillation threshold, Am. J. Physiol. 201:457, 1961. LO. Turnbull, -4. D., MacLean, I*. I )., I.)obell, A. R., and Demers, R.: The influence of hyl’erb;lric oxygen and of hypoxia on the ventriclllar librillation threshold, J. Thorac. Cardiovahc-. Surg:. 50:842, 1965. 71. Gerst, 1’. H., Fleming, \f:. H., and Maim, J. I~.: ‘1 clI~;lntitative evaluntion of Lhe effects of :lcidohi.s ;~rltl alkllosis upon the venlrkml;~r iil)rill.il ion lhrcshold, Surgery 59:1(150, IYOfi. 17. \\‘igqtlrs. C. _),, \Vegria. K.. and I’iner,t, R.: The did5 (,I n1~orarcli,~l isc.llcllli.l (11~ 1111. 6.
II
.
23.
24.
25.
fibrillation threshold-The mechanism of spontaneous ventricular fibrillation followinp coronary occlusion, Am. J. Physiol. 131:309, 1940. Shumwav. N. E.. Iohnson. 1. A.. and Stish. R. J.: ‘I%e study’ o? ventricular fibrillation by threshold determinations, J. Thorac. Cardiovast. Surg. 34:643, 1957. Rosati, K. A., Alexander, J. A., Wallace, A. G., Scaly, \V. C., and Young, W. G.: Failure of beta adrenergic blockade to alter ventricular fibrillation threshold in the dog, Circ. lies. 19:721, 1966. Hoffman, B. F., Siebens, A. A., Crantield, I’. l:., and Brooks, C. McC.: The effect of epinephrine
26.
27.
28.
and norepinephrine on ventricular vulnerability, Circ. Res. 3:140, 1955. Lown, B., and Cannon, R.: Electrical stimulation to estimate the degree of digitalization, Am. J. Cardiol. 22:251, 1968. de Gubareff, T,, and Sleator, \I’.: F:ffects of caffeine on mammalian atrial muscle and its interaction with adenosine and calcium, J. Pharmacol. Exn. Ther. 148:202. 1965. Tempte, S. V.‘, and Davis, I,: D.: Effect of calcium concentration on the transmembrane potentials of Purkinje fibers, Circ. Res. 20:32, 1967.
R
ecently, our laboratory as well as others has been interested in studying the various stress effects of caffeine such as the elevation of plasma adrenocortical steroid concentrations, blood free fatty acid levels, and adrenergic effects.‘es In addition, caffeine may increase the concentration of cyclic adenosine monophosphate (AMP) by competitive inhibition of phosphodiesterase and may decrease the binding of Ca++ by the cell membrane.gj10 Because some of these pharmacologic effects are known to induce ventricular fibrillation,11~‘3 it would be of interest to study the effect of caffeine on the ventricular fibrillation threshold (VFT), The aim of the present work was to study the effect of caffeine on the VFT in normal dogs and in dogs with experimentally-
induced myocardial infarction during the acute stage of the occlusion. In order to evaluate the relation of the changes in VFT after the administration of caffeine to the adrenergic effects, experiments were also performed after pretreatment with propranolol and with practolol. Methods
and
materials
Mongrel dogs weighing 25 to 30 pounds were anesthetized intravenously with sodium pentobarbital, 25 mg. per kilogram of body weight. Respiration with room air was maintained by means of a Harvard ventilatory pump through an endotracheal tube. Tidal volume and respiratory rate were set according to the weight of the animal, utilizing the ventilatory graph prepared by Kleinman and Radford. Arterial
From the Division of Cardiology, Philadelphia General Hospital, Philadelphia. Pa. This work was aided by Grant No. 71-589-l from the Commonwealth of Pennsylvania and by the Foundation for Cardiovascular Research, Philadelphia, Pa. Received for publication Oct. 15, 1971. Reprint requests to: Samuel Bellet, M.D., 2021 Spruce St., Philadelphia, Pa. 19103. *Director, Division of Cardiology, Philadelphia General Hospital; Professor of Clinical Cardiology, Graduate School of Medicine of the University of Pennsylvania; and Lecturer in Pharmacology, University of Pennsylvania SchOol of Medicine. **Cardiology Chief Resident, Division of Cardiology, Philadelphia General Hospital. ***Cardiologist, Division of Cardiology, Philadelphia General Hospital. ***Research Fellow, Division of Cardiology, Philadelphia General Hospital. *****Research Associate, Division of Cardiology. Philadelphia General Hospital.
l,‘ul.
N, No.
2, pp. 21522i
August,
1972
American Heart Journal
215
III
Ipig. 1. Determilution of the ventricular fibrillation threshold (VFT) by delivering (G) through previously implanted epicardial electrodes. S, pacemaker stimulus; F, ventricular fibrillation. Note the progressive increase of the amplitude of the gated
pH, E’co~, and Pas were monitored by the use of a radiometer. The values did not show significant deviation from the normal. The temperature was recorded every 15 minutes by means of a rectal thermometer. The electrocardiogram (ECG) was monitored through an oscilloscope and recorded each time the VFT was measured with a Sanborn Viso-100 recorder at a paper speed of 50 mm. per second. The blood pressure was measured by means of a catheter inserted in the descending aorta
gated series of impulses R, vwtricular complex; impulse (G’) from I to III.
3
utilizing Statham 23Bd transducers and Electronics-for-Medicine amplifiers. Two groups of experiments were performed. In the first group the ventricular fibrillation threshold (VFT) was determined in intact dogs by delivering electrical impulses through the chest ~vall. In the second group the impulses were delivered directly to the heart through previousI)’ implanted epicardial electrodes. These electrodes were attached to insulated wires wl~ich were exteriorized through the chest
7’uOl~~
i. j;)O;d
of
sorlirtm
bcn~otrfc
on
the
ventricular~fibrillation
Minules
after
~--~__-_-~Ihg 0 I. 2. , :; : .5 . (I. 7.
-
I
15
0. sot 0.45 0.45 0.35 0. 70 0.50
0.50 0.45 0.40 0.35 0. 70 0.50 0. 70 0. 60 0.30 0.40
0.70 0.60 0.30 0.45
h. 0. II). .~-
I
(llliil.)
intact
yzormul
dogs*
injection
45
30
in
I
0.50 0.45 0.40 0.35 0.70 0.50 0.75 0.60 0.20 0.45
60
90
0.55 0.45 0.40 0.40 0.70 0.50 0.75 0.45 0.20 0.55
0.50 0.45 0.40 0.35 0. 70 0.50 0.75 0.45 0.25 0.55
Mean diflerence
No. qf dogs
0
10
15
10
30
10
45
10 10 10
60 90
intravenous ~_~_____
0.45 0.50 0.40 0.40 0.70 0.45 0.70 0.60 0.30 0.45
I The after clrztg admin.
threskold
Mean VFT (mutt-sec.)
0.50 0.49 0.495 0.49
0.495 0.49
*Dosage 12.5 mg. per kilogram of body iVFT in watt-seconds. $Differences not statistically significant
jrom
0 lime value (watt-sec.)
VlViCkllU
S.E. M.
0.01 0.005 0.01
0.0444 0.00136 0.00155
0.067 0.011 0.012
0.005
0.0058 0.0043
0.024 0.02
0.01
t
I’
0.149 0.454
N.S.$ N.S.
0.833 0.208 0.50
N.S. N.S. N.S.
wei::ht. at the 5 O,b 1~x1
on the basis
wall and were thus available for stimulalion. GYOZI~IA. In the first group (Group A, intact dogs), a method similar to that described by Lou-n, Kleiger, and Williams13 was utilized. Caffeine and control experiments were performed on normal dogs and on dogs with acute myocardial infarction. Tile method is briefly as follows. Two electrode paddles measuring 8?4 cm. in di;ulleter covered with conductive paste were q~plied with pressure externally on both sides of the shaved chest at the level of the apical thrust. These paddles were held in a fixed position with rubber straps across the chest. Electrical discharges were delivered utilizillg tlie Idown Cardioverlrr RIodel 10530-H \\,itll ;t 16 nlicrofarad crrpac.itor ~ltrough 3 100 millihenry inductor. A voltage-dividing network was connected in series with the electrodes in order to obtain
of a pailed
corn~~arison.
accurate measurement of the discharge ;~t the range of 0- to 10 wsec. [watt-seconds) at increments of 0.05 wsec. The fibrillation threshold was determined by sweeping the Q-T interval of the cardiac cycle with stimuli of increasing energy from subthreshold to threshold levels. This was performed by progressively increasing the delay of the stimulus from the peak of the R wave by increments of 10 milliseconds using a 15 to 20 second interstimulus interval. The criterion of the VFT was tile minimal energy producing ventricular fibrillation for at least 10 seconds. The presence of ventricular fibrillation was established by tlie I<(‘(; and the disappearance of pulsatile aorlic: 1)ressure (I;ig. 1). Collll1.ersl~ocks\\,i 111energy ranging frunl SO to 2~) wsec. \vc’re applied in order to convcrl ventricular fibrillation to normal sinus rhythm. After an episode of ventricular
lirl~e
II. Efect
of cufeine
sodium
benzoute
on ventricz{lurJiDrilllltion
threshold
in iduct
normd
dOgS*
1. 2.
0.651 0.50
0.50 0.50
4: 3 5. 0. 7. 8. 9. 10. 11.
0.50 0.40 0.50 0 4.5 0.50 0.55 0.35 0.70
0.50 0.40 0.40 0.45 0.45 0.45 0.55 0.30 0.70
----
0.55 0.35 0.40 0.35 0.35 0.40 0.50 0.35 0.50 0.30 0.60
_______ ~~______
.~-__
0.50 0.30 0.40 0.35 0.30 0.35 0.40 0.30 0.40 0.30 0.60 .-....
0.55 0.30 0.45 0.35 0.35 0.25 0.35 0.30 0.30 0.25 0.50
0.40 0.35 0.45 0.35 0.35 0.35 0.35 0.40 0.40 0.25 0.55 ___--~-
--~
~
Mean Time after admin. of cizffeeine (min.)
0 1.5 30 4.5 60 90
_
difference
No. of dogs
Mean VFT (watt-sec.)
11 11 11 11 11 11
0.509 0.473 0.423 0.382 0.359 0.382
*Dosage 25 mg. per kilogram tVFT in watt-seconds.
of body
from
0 time value (watt-sec.)
0.036 0.086 0.127 0.150 0.127
Variance
S.E.lf.
0.002546 0.001307 0.002682 0.005500 0.003182
0.0152 0.0110 0.0120 0.0224 0.0170
t
3.368 7.818 10.580 6.696 7.470
’
P
0.05 0.001 0.001 0.001 0.001
weight.
fibrillation, a period of at least 10 minutes was allowed before a new series of stimuli were applied. The ventricular fibrillation threshold (VFT) jvas determined in 11 normal dogs at 1.5 minute intervals before and for a period of 90 minutes after intravenous injection of 25 mg. per kilogram of body weight caffeine sodium benzoate (corresponding to 12.5 mg. per kilogram of body weight caffeine base). Control experiments, of the same duration in which sodiunl benzoate (12.5 mg. per kilogram of body weight) was injected, were performed in 11 other dogs. Similar studies wcrc pcrforlned ;Jso in dogs during tlie acute phase of Ilt)*ocardial infarction produced I)y t\\o-stage ligation of the anterior descending artery.‘4 Tile
experiments mere performed on the fourth day after coronary ligation because in an earlier stage the presence of frequent prcmature ventricular contractions interferes with the proper determination of the VFT. Caffeine experiments were performed in 11 dogs with acute infarction, whereas control experiments were performed in 6 such dogs. In addition, similar experiments were performed on 9 normal animals treated 1)~ a combination of caffeine sodium benzoatc (25 mg. per kilogram of body weight) and propranolol (0.2 mg. per kilogram of 1)ody weight). Five other animals were treated \vith intravenous injections of propranolol (0.2 n1g. ])c:I- kilogr;ml (of Iwd)~ \\.cigllt) ;IlOW. C;rozc,b f3. In tile second group of experiments (( ;roup 13, dogs with pre\iously itrl-
‘I’trblt: III. Effect of so&m bipolar ,implanted electrodes
benzoate on the ventricular jibridlafion threshold in nomad dogs with (third to seventh day after implantation)* Minutes
1. I ;: 1. .i. 0. 7. 8. 0. 10.
after
intravenous
injection
14t
16
14
16
16
16
15
18 16 16 12 10 9 17 12 12
17 15 18 11 0 11 1Y 11 12
18 13 18 11 10 10 20 11 12
18 16 16 13 10 10 18 11 13
15 19 15 13 9 10 19 12 9
1.5 19 18 11 10 11 19 12 12
13 I6 12 10 0 18 10 14
t
P
.__.~ Time after admin. of sodium benrnate (min.)
0 15 30 45 60 90 110
NO. of dogs
Mean VFT (Ma.)
10 10 10 10 10 10
13.6 13.9 13.7 14.1 13.7 14.3 13.0
Mean difference from 0 time oalue (Ma.)
I Vaariunce
S.E.M.
1
0.3 0.1 $0.5
2.233
0.47
0.64
0.7222
0.269
1.859
+::: -0.3
1.555 2.4444
0.394 0.494
1.776 0.668
N.S.~ N.S. N.S. N.S. N.S. N.S.
*Dosage 12.5 nx. per kilograni of body weight. IVFT in milliamperes. :Differences not statistically significant.
planted electrodes), electrical discharges were delivrered directly to the myocardium Iq means of specifically constructed bipolar epicardial electrodes implanted on the right ventricle three to seven days prior to the experiment. These electrodes consist of two stainless steel wires, 1 mm. in diameter, embedded 10 mm. apart in a small acrylic plaque. They were connected to Tefloncoated treated silver lvires which were exteriorized through the chest wall. The heart rate \vas kept constant during each experinient 1)~ pacing the right atrium at a rate above the spontaneous rate of the animal by means of a similar pair of implanted elec~trotl~5. An American Elwtronics Lalb w;~s rrtilized for this orator\~ stiiilulator impulse \vas douplll-~)OStZ!.Tire pacennkr I,le the pacing tliresliold in intensity and
VFT
Contrai ,“ormall
05
Wa’t’sec. :;I!%, I5
30
45 Ttme (mini
i--Id
60
75
90
Fig. 2. ‘The effect of caffeine on the VF’T of normal dogs and dogs with acute myocardial infarction (impulses delivered through the chest wall). No change in the normal rontrols. 1;oIlowing caffeine drni~~ihtralion, the \‘l;‘I‘ drops. ‘I’he colrll-ol value< of dogs with acute mpcardial infarctirm (.A All) de lower than Iumrtl. b’urther tlet~.~~ is oljherved after caffeine.
220
Am. Heart 1. August. 1972
Bellid et ul.
l’uhle IV. l’he qfects of cclfleiae sodium bensoute on the T/F1 fAuntcd c~lrctrodcs (third to seventh duy after implantation)*
in normtrl
dogs with
lzipolllr
im-
Minutes after intrave~zous injection
Mean
Tinze after adnzin. of caffeine (min.)
0 15 30 45 60 90 120
No. of dogs
Mean VFT (Ma.1
10 10 10 10 10 10 10
14.6 11.6 9.2 9.6 10.9 13.5 14.2
*Dosage 0.25mg. per kilogram of body tVFT in milliamperes. tIXfferences not statistically significant.
difference from 0 time value (Ma.)
3.0 5.4 5.0 3.7 1.1 0.4
Varariance
12.8888 6.2800 6.0000 6.6777 6.5444
S.E. M.
1.135 0.836 0.775 0.817 0.809
t
P
2.643 6.459 6.452 4.529 1.360
0.05 0.001 0.001 0.01 N.S.# N.S.
weight.
2.5 msec. in duration. The VFT was determined by delivering gated impulses to the right ventricle through the previously implanted bipolar electrodes utilizing a method similar to that of Han.15 These impluses were programmed using a series of Tektronix waveform and pulse generators which trigger a Grass stimulator (model SDS). At every tenth heart beat, this system delivers a series of rectangular pulses of 2.5 msec. duration each at intervals of 10 msec. The series of impulses starts immediately after the R wave and ends at the peak of the T wave, adequately covering the vulnerable period. The cllrrent inrr-eased at increnients of 1 l\la. ulitil veil-. tricular fibrillation \vas observed (Fig. 1). The current delivered to the dog was measured with a current probe amplifier
and displayed on an oscilloscope. Ten control and 10 caffeine experiments were performed on normal dogs. In addition, 5 experiments were done on animals treated by the combination of caffeine sodium benzoate (25 mg. per kilogram of body weight) and practolol (0.6 mg. per kilogram of body weight). Results Control and caffeine experiments 016 IIOYrnul dogs. In Group A (intact dogs), no change in the VFT was noted during the 90 minutes following the injection of sodium benzoale. In conLrast, after injection of caffeine sodium I)enzoate a significant decrease in the fibrillation threshold was noted at 1.5, 30, 45, 60, and 90 minutes after the injection. The maximum effect
l’rllde V. fib/h of sodium htsoutc on the ventriculur myoccudicil 2nfWction (foltrth postoperc~tivc day)* Minutes __-
--__-
after
$/X&ion
intrave?tous
threshold in dogs with clctdte
injection ____
Dog
1. 2. .3 . 4. 5. 6. 7. 8. 9. 10.
0
15
0.50t 0.50 0.45 0.40 0.35 0.20 0.30 0.50 0.45 0.25
0.45 0.55 0.45 0.45 0.35 0.20 0.30 0.45 0.45 0.25
30
I
I
0.45 0.55 0.40 0.45 0.35 0.20 0.30 0.45 0.40 0.25
45
/
0.45 0.55 0.40 0.45 0.45 0.20 0.30 0.45 0.40 0.25
60
90
0.45 0.55 0.45 0.40 0.30 0.20 0.30 0.45 0.45 0.30
0.50 0.50 0.45 0.35 0.30 0.20 0.30 0.50 0.45 0.30
I_-
__-_
Time after drug admin. (min.)
0 15 30 45 60 90
No. of dogs
Mean VFT (watt-sec.)
10 10 10 10 10 10
0.39 0.39 0.38 0.39 0.385 0.385
*Dosage 12.5 mg. per kilogram of body tVliT in watt-seconds. tlXfferences not statistically significant
Mean difference jronz 0 t&e value
0 0.01 0 0.005 0.005
Variance
S.E.M.
0.00155
0.012
0.00136 0.00081
0.011 0.009
t
0 0.833 0 0.45 0.55
P
N.S.t. N.S. N.S. N.S. N.S.
weight. at the 5yo level
on the basis
\\XS noted at about 45 and 60 minutes, when the mean VFT decreased to 0.382 and 0.359 wsec. from a control value of 0.509 wsec. (P < 0.001) (see Tables I and 11, and Fig. 2). Similar results were observed in Group B (normal dogs with previously implanted epicardial electrodes) (see Tables III and IV, and Fig. 3). There was a statistically significant decrease in ventricular fibrillation threshold at 15, 30, 45, and 60 minutes with a maximum effect at about 45 and 30 minutes (9.6 and 9.2 respectively, from a control value of 14.6 Ma., p < 0.001). There was no change in the control experiments (i.e., after the injection of sodium benzoate). Dogs with experimental myocardial infarction (caffeine and control experiments.). The results obtained in this group of dogs are
of a paired
comparison.
nh,
Fig. 3. The effect of caffeine on the VFT of normal dogs (impulses delivered through previously implanted epicardial electrodes). There is a decrease in VFT after caffeine administration while there is no change in the controls and in those treated with the combination of caffeine and practolol.
_____ I
_____--_I__
Peg
1. 2. 3. 4. .5 . 6. 7. 8. 9. 10. 11.
0
15
0.4ot 0.25 0.50 0.40 0.30 0.40 0.60 0 ,40 0.35 0.30 0.60
0.30 0.20 0.35 0.35 0.25 0.35 0.60 0.40 0.35 0.25 0.60
_-_I------.-_____-----~~ 30
I
.---I
I
45
60
0.25 0.30 0.30 0.30 0.20 0.35 0.55 0.45 0.30 0.30 0.35
0. ‘0 0.30 0.30 0.25 0.20 0.30 0.60 0.45 0.35 0.35 0.35
~-.
-.
(/f>
I 0.25 0.25 0. 30 0.30 0.25 0.35 0.60 0.40 0.30 0.30 0.10
0.30 0.30 0.30 0.35 0, to 0.35 0.55 0 .4.5 0.35 0.35 0. 3.T
--_-__--
Time
Xean diference
after
admin.
of
cafe&e (min.)
0 1.5 30 4.5 60 90
No. of dogs
11 11 11 11 11 11
Mean VFT (watt-sec.)
0.409 0.364 0.327 0.323 0.314 0.332
from 0 time
-0.045 -0.082 -0.086 -0.095 -0.077
given in Tables 1: and \iI and in Fig. 2. 111the control experiments, no significant cllange in the VF’I‘ occurred, whereas after caffeine administration the VI!?’ was significantly decreased at 15, 30, 45, 60, and 90 minutes (p < 0.01). The maximum effect was noted at 45 and at 60 minutes \vhen the mean VFT decreased to 0.323 and 0.314 Ivsec., respectively, from a control value of 0.409 wsec. As expected, the VFT before the injection of caffeine (0.409 jvsec.) was lower in dogs with acute myocardial infarction than in normal dogs (0.509 wsec.). Administration
of
the
Vuriance
S.E. Al.
0.002227.5 0.00464 U.OO7046 0.009228 0.008182
0.0142 0.0206 0.0253 0.0289 0.0273
t
i
I’
value (watt-sec.)
conzbinations
of
cclzeine und $wopranolol and cafe&e and practolol. As seen in Table VII, propranolol in the dose of 0.2 mg. per kilogram of bodl Lveight did not significantly affect the VFT. However, lvhen administered simultaneously with caffeine, it prevented the caffeine-induced decrease in VFT. This is
3.169 3.981 3.399 3.287 2.825
show71in ‘I’al~le \.I II, where no clinngc in VFT is ol)served after the ~tdnlirlistratiorI of the propranolol-caffeine combinatiofl (Fig. 4). Similarly, no change in YE-T \t’;ls observed in the dogs treated with caffeincb and practolol (Table IX). Discussion 1. Til1lle.s
of ventriclllar
Jibrillation
thresh-
oZd. The values of VFT obtained in Group A (intact dogs) are in the range reported by Lawn, Kleiger, and Williams13 who employed a similar method. Those obtained in Group B (dogs with previously irnplanted electrodes) were similar to the results of Han,15 who utilized a similar technique. There w-asno change in the VFT in the control experiments. Prolonged anesthesia and repeated determinations did not significantly affect the VFT in the control experiments. This has been reported 1)y
Minutes
1. 2. 3. 1. 5. ~- _____-
0. 70t 0.50 0.35 0.80 0.35
0.70 0.50 0.35 0 80 0 35
before
(-)
0.80 0.50 0.35 0.80 0.35
and after
(+)
intrmenous
0.80 0.40 0.35 0.70 (1.35
injection
0.70 0.50 0.35 0.90 0.10
0.60 0.50 0.35 0.80 0.35
0.60 0.40 0.35 0.90 0.30
I_--
Meun T’FT (ml&ser.)
Xenn di$erenre jrorn 0 time control (wnlt-sec.)
others.1”~‘7 Although some variation in the control values of \‘FT between the groups of experiments was observed, these differences are not Statistically significant. ‘1 -. The efect of ccl$eine on the I’FT of noumciZ dogs. In contrast to the control experiments, caffeine produced a significant decrease in the \‘FT n:hich lasted at least 60 minutes. It is of interest that similar results were obtained with both techniques (Ciroups A and B). This is important, since the accurate determination of VFT is relatively difficult as it is affected by many variables and each technique is characterized by specific advantages and disadvantages.r8-?r The closed-chest technique, with impulses delivered through the chest wall of the intact animal, involves the problem of the chest wall impedance which might vary from dog to dog or from moment to moment on the same dog, but this technique does offer the advantage of using intact animals without previous operations. On the other hand, the technique utilizing implanted electrodes bypasses the problem
0
Fig. 1.
I5
The effect induced decrease of there is no decrease of the combination
30
45 Time
60
75
so
(men)
of propranolol on the caffeineVFT in normal dogs. Note that in VFT after the administration of caffeine and propranolol.
of variable impedance as well as the openchest problem, but introduces the factor of clot formation, electrode implantation, or myocardial reaction around the implanted electrode. Open-chest techniques were avoided in this study since they introduce important physiological alterations. 3. Eflect of caffeine on the b’FT of dogs
6. 7.
8. 9.
0.30t
0.30
0.45 0.30 0.75 0.80 0.70 0.60 0.40 0.35
0.15
0.35 0.45 0.25 0.70 0.80 0.70 0.60 0.30 0.40
0.50 0.30 0.75 0.80 0.60 0.60 0.40 0.40
0.35 0.45 0.30 0.75 0.80 0.60 0.60 0.40 0.40
0. hO 0.60 0.4) 0.40
l’oria~ce
S. E. ‘II.
t
I’
0.00382
0.0205
1.356
0.35 0.45 0.30 0.75 0.80 0.80 0.70 0.30 0.40
0.30 0.70 0.80 0.70 0.60 0.40 0.35
0.35
0.3.5
0.45 0.30 0.75 0.80
Mean Time after drug admin.
(mk)
No. of dogs
Mean
VFT
(watt-sec.)
difference front 0 tinre control (watt-sec.)
0
15 30 45 60 90
9 9 9 9 9
0.511 0.539 0.506 0.506 0.516 0.516
SO.028 0.005 0.00s 0.005 0.005
*Dosage caffeine sodium benzoate = 25 mg. per kilogram tVFT in watt-seconds. iD,ffI erences not statistically significant.
of body
with acute myocardial infarction. The VFT of dogs with acute myocardial infarction was lower than that of normal dogs. During the fourth day after coronary ligation, the heart muscle manifests the characteristic pathology of acute myocardial infarction and one would anticipate that the VFT would be below normal. These results are in agreement with observations of others who observed significant decrease in the VFT in ischemic hearts.15J2*23In dogs with acute myocardial infarction, the VFT which had been lowered because of ischemia was further decreased by caffeine. This might conceivably facilitate the development of spontaneous ventricular fibrillation (and sudden death) when myocardial ischemia and caffeine are operating simultaneously. 4. The efect of the combination of cafe&e and beta blocking agents on the VFT. As has been reported by others, propranolol (0.2
weight;
dosage
~~royranolol
= 0.2 mg. per kilogram
N.S.f N.S. N.S. N.S. 1N.S.
01 body
wcigl~t,
mg. per kilogram of body weight) did not affect the VFT to any significant degree.“4 However, propranolol probably prevented the caffeine-induced decrease in VFT whcu administered simultaneously with it. This effect is related to the beta-blocking actiou of propranolol rather than to its “quinidine-like” effect, since similar results were obtained by the use of practolol and “pure” beta-blocking agents which do not have significant direct action on the cardiac muscle. The dogs receiving this combination behaved similarly to the controls. These results would suggest that the effect on the fibrillation threshold may be mediated directly or indirectly through the adrenergic mechanism. It has been shown that sympathetic nerve stimulation results in an accentuation of asynchrony of recovery of the myocardial excitability leading to a marked decrease in VFT. Exogeneous catecholamine administration has the same
T&e IX. Effect of the combkation of caffeine sodium benzoate plus practolol on the ventricular fibrillation threshold in normnl dogs with bipolar implanted electrodes (third to seventh duy clfter implant&ion) * Minutes
after
30
1
i&ravenous
injection
Dog 0
/
15
1
45
1
60
/
90
/
120
-
1. 2. 3. 4. 5.
l‘inle after drug admin. (min.)
No. of dogs
Mean VFT (Ma.)
0 15 30 45 60 90 120
5 5 5 5 5 5 5
10.4 10.2 10.6 10.6 10.0 10.0 10.4
Mean difference from 0 time value (Ma.)
0.2 0.2 0.2 0.4 0.4 0.0
Variance
S.E.M.
0.70 1.70 2.20 1.30 1.30
0.38 0.59 0.67 0.51 0.51
*Dosape caffeine sodium benzoate = 25 mg. per kilogram of body weight; dosage practolol tVFT in milliamperes. IDifferences not statistically significant at the 5 % level on the basis of a paired comparison.
effect in the initial 5 to 10 minutes after administration.l’~25 Since caffeine results in stimulation of adrenergic activity,5v6 it may decrease the VFT through this mechanism. 5. Mechanism of decrease of VFT by ccL$eine. Caffeine has many pharmacologic effects which might be anticipated to affect the VFT. These include adrenergic stimulation, direct myocardial stimulation with increases in cardiac output, contractility, cardiac work, oxygen uptake, and coronary A-V difference. Agents, such as catecholamines and digitalis,n,25z26 producing similar effects are usually associated with depression of the VFT. A mechanism by which caffeine decreases the VFT is the adrenergic stim~ll;ltion Liorl of
rllwliouetl
ahove.
The
pre\w-
tile c~;~ffeiIlr-i~lduc-~(l dtxcreasr in \‘l;‘l‘ 114’ ~~~~pr;molul or practolol supports (Ilk view. ‘I’lle elevation of serum free fatty acid levels after caffeine administration rnny coutribute to this effect.‘a2 A rela-
0.53 0.33 0.30 0.78 0.78
= 0.6 trig. per kilogram
N.S.f N.S. N.S. N.S. N.S. N.S. of body
weight.
tion between serum free fatty acids and arrhythmias and death after acute myocardial infarction has been reported by a group of investigators. In addition, caffeine increases intracellular 3’,5’-cyclic AMP by inhibiting phosphodiesterase, elevatesserum adrenal steroid levels, and probably directly affects the action potential.1°J7 The factors mentioned above, singly or collectively, could result in facilitating the development of re-entry which under certain conditions might lead to ventricular fibrillation. The effect of caffeine on calcium may also play a role. Caffeine decreases the calcium binding which may lead to an increased concentration of calcium in the cell.9 Calcium was found to cause a reduclion in the maximum rate of rise of the xtion potential, which can slow tile \,ttlociLy of impulse propagation and shortens the refractory period. These effects would favor the development and maintenance of re-entrant excitation and possibly
226
Bellet et (11.
fibrillation.2* cium may
Irnder centain conditions calinitiate \Tentricular fihillation.‘”
Summary The effect of caffeine administration on the \TFT was studied in normal dogs and in dogs \vith acute myocardial infarction. TWO methods \vere employed; the first utilized impulses delivered through the chest wall of the intact animal and the second used epicardial electrodes implanted four to se\.en days previously. Caffeine produced a decrease in \.‘E’T starting 1.5 minutes after injection and tllis effect lasted about 60 minutes. I’ropranolol and practolol prevented tile caffeine-induced decrease of VFT. In dogs with acute myocardial infarction the \,-I!‘~ \\-a~ lo\i:er than normal and was further decreased after caffeine administration. Although the dose of caffeine utilized in this study is higher than that usually consumed by humans, it is possible that lower doses have a significant effect when combined with other agents. The various factors that affect the VFT w+ich might have arrhythmogenic effects are presently under study. There is suggestive evidence that a number of factors might be cumulatively significant in susceptible individuals. These factors may include cigarette smoking, various degrees of stress effects due to anxiety and exertion, various drugs--i.e., isoproterenol, ephedrine, and several sympathomimetic agents, and caffeine. The role of caffeine requires further study in this regard. REFERENCES 1.
2.
3.
4.
5.
Bellet, S., Kershbaum, .%., and Aspe, J.: The effect of caffeine on free fatty acids, Arch. Intern. Med. 116:750, 1965. Bellet, S., Kershbaum, A., and Fin&, E. M.: Response of free fatty acids to coffee and caffeine, Metabolism 17:702, 1968. Bellet, S., Kostis, J. B., Roman, I,., and UeCnstro, 0.: Effect of coffee ingestion 011 adrenocortical secretion in young men and dogs, Metabolism X3:1,007, 1969. DeSchaepdryver, A. F.: Physiopharmarological effects on suprarenal secretion of adrenaline and noradrenaline in dogs, Arch. I II~. I’h;lrm:~ctdy~i. ‘I‘hcr. 119:517, 19.50. Levi, I..: The effect of c,offee on the funcl ion of the s?nll)~~~l~o-adreno-lnedltll~~ry syste111 in mnu,
Acta bled. Srand. 181:431, 1967. Bellet, S., Roman, L., DeCastro, I)., Kitn, Ii. E., and Kershbaum, A.: Effect of coffee ilrgestion 011 catecholnmine release, Metabolism 18:288, 1969. ;\., Khorsandian, I:., Cal)l;~~l, 7. Kershbaum, R. E‘., Rellet, S., and Weinberg, I..: The role of c;~tccholnmines in the free fatty acid respouze to cigarette smoking. Circulation 28:.52, 196.1. A., Bellet, S., Jimellez, J.. :LII~ 8. Kershballm, Feinberg, I,. J.: Difference in effects of cigar and cigarette smoking on free fatty acid mobilizatiotl and catecholamine excretioll, J.A.M.:1. 195:1095, 1966. A., and Grollman. 1;. I;.: I’harnl,l0. Grollman, cology and therapeutics. 7th ed., I.ea & Febi~er. I’hiladelphia, 1970, p, 201. IO. Sutherland, E. \\~., Kobison, G. A., :llld Butcher. Ii. \Y.: Some aspects of the biolopical role (11 adenosille 3’.5’ monophosl)hate (cyclic ,111 I’), Circulation X:279, 1968. J., deJalon, I’. G., and kloe, G. K.: 11. Han, Adrencrgic effects on ventricular vulnerability, Circ. Kcs. 14:.516, 1964. l.., Howard, S. \I:., and Merrill, 12. Grumbarh, L.. I.: 1;artvrs related to the initiation of veiltricul;u fibrillation in the isolated heart. Efiect of calcium and I,otassium, Circ. Kes. 2:452. 1954. Ii., and \Villiams, J.: Cardio13. I,uwn, B., Kleiger, version and digitalis drucs: Chanced threshold to electric shock in digitnlized animals, Circ. Res. 17:519, 1965. A1. S.: I)elayed development of ven14. Harris, tricular cctopir rhythms following experimental coronary occlusion, Circulation 2:1318, 19.50. vulnerability during acute 15. Han, J.: \,Yentricular roronarqocclusion, ,\nl. J. Cardiol. 24:857, 1969. II. I)., Starmer, F., and \\‘halcn, 16. 1Irlntosh, Ii. E.: A comparison of the electrical ventriclllar librillation threshold with and without nnesthe&. .-\M. HEART J. 72:419, 1966. M.: Bretvlium tosylate for suppression 17. Fktcaner, of induced ventkcular tibrillation, Xm. J. Cardial. 17:528, 1966. C. Xl., Levy, I.. M., and b’Iacl.e;ul, 18. Phibbs, I*. I).: The influence of temperature and corenary occlllsion on the ventricular fibrillation threshold, Surg. Gynecol. Obstet. 109:216, 1959. 19. \~anTyr~. Ii. i\., and -\lacl,ean. I*. I).: YentrictlIar librillation threshold, Am. J. Physiol. 201:457, 1961. LO. Turnbull, -4. D., MacLean, I*. I )., I.)obell, A. R., and Demers, R.: The influence of hyl’erb;lric oxygen and of hypoxia on the ventriclllar librillation threshold, J. Thorac. Cardiovahc-. Surg:. 50:842, 1965. 71. Gerst, 1’. H., Fleming, \f:. H., and Maim, J. I~.: ‘1 clI~;lntitative evaluntion of Lhe effects of :lcidohi.s ;~rltl alkllosis upon the venlrkml;~r iil)rill.il ion lhrcshold, Surgery 59:1(150, IYOfi. 17. \\‘igqtlrs. C. _),, \Vegria. K.. and I’iner,t, R.: The did5 (,I n1~orarcli,~l isc.llcllli.l (11~ 1111. 6.
II
.
23.
24.
25.
fibrillation threshold-The mechanism of spontaneous ventricular fibrillation followinp coronary occlusion, Am. J. Physiol. 131:309, 1940. Shumwav. N. E.. Iohnson. 1. A.. and Stish. R. J.: ‘I%e study’ o? ventricular fibrillation by threshold determinations, J. Thorac. Cardiovast. Surg. 34:643, 1957. Rosati, K. A., Alexander, J. A., Wallace, A. G., Scaly, \V. C., and Young, W. G.: Failure of beta adrenergic blockade to alter ventricular fibrillation threshold in the dog, Circ. lies. 19:721, 1966. Hoffman, B. F., Siebens, A. A., Crantield, I’. l:., and Brooks, C. McC.: The effect of epinephrine
26.
27.
28.
and norepinephrine on ventricular vulnerability, Circ. Res. 3:140, 1955. Lown, B., and Cannon, R.: Electrical stimulation to estimate the degree of digitalization, Am. J. Cardiol. 22:251, 1968. de Gubareff, T,, and Sleator, \I’.: F:ffects of caffeine on mammalian atrial muscle and its interaction with adenosine and calcium, J. Pharmacol. Exn. Ther. 148:202. 1965. Tempte, S. V.‘, and Davis, I,: D.: Effect of calcium concentration on the transmembrane potentials of Purkinje fibers, Circ. Res. 20:32, 1967.