Journal of Clinical InvestigationVol. 43, No. 9, 1964

The Effect of Acetylcholine and Potassium onRepolarization of the Heart *

CHARLESFISCH, SUZANNEB. KNOEBEL, ANDHARVEYFEIGENBAUMt

(From the Division of Cardiology, Department of Medicine, and the Heart Research Center,Indiana University School of Medicine, and the Krannert Heart Research Institute,

Marion County General Hospital, Indianapolis, Ind.)

Acetylcholine has been shown to have an effecton the action potentials of mammalian atrialmuscle, the sinoatrial and the atrioventricularnodes, and on the action potential of frog ven-tricles (1-4). On the other hand, the action po-tential of mammalian ventricle has been found tobe highly resistant to acetylcholine. Only veryslight changes were noted in the presence of enor-mous concentrations of the drug (4-6).

The purpose of this communication is to pre-sent electrocardiographic evidence indicating a)that acetylcholine exerts a consistent effect on re-polarization of the ventricles in the intact dog andthat this effect is independent of the heart rate,ventricular arrhythmias, and atrioventricular(AV) or intraventricular conduction delays, andb) that the effect of acetylcholine on repolariza-tion is augmented by increasing the level of plasmapotassium (K).

Methods

Eleven experiments were performed with seven mon-grel dogs weighing 10 to 14 kg. The animals wereanesthetized with either pentobarbital, 30 mg per kg iv,or a combination of morphine sulfate, 2.5 mg per kgim, followed by pentobarbital, 15 mg per kg iv. Ventila-tion was maintained through the use of a Harvardrespirator. A bilateral cervical vagotomy was per-formed, and an arterial catheter was placed just abovethe aortic valves. Blood pressure was continuously re-corded through a Cournand needle in the femoral artery.The entire experiment was monitored with an oscilloscope,and permanent records were obtained with a direct-

* Submitted for publication January 10, 1964; ac-cepted May 15, 1964.

Supported by the Herman C. Krannert Fund, the In-diana Heart Association, Indiana State Board of Health,in part by U. S. Public Health Service training grant5363, and in part with facilities provided by cardiovas-cular clinical research grant H-6308 from the NationalHeart Institute, U. S. Public Health Service.

t Work done as trainee of the National Heart Institute.

writing electrocardiograph using standard lead II con-nections. Frequent determinations of arterial plasma Kwere made with a Beckman flame photometer.

Increasing amounts of acetylcholine were injectedthrough the catheter for 15 seconds until a total amountwas reached that consistently induced second or thirddegree AV block. With an electric interval timer thisamount of acetylcholine was then given every 2 min-utes without interruption throughout the experiment.Four to eight injections of this dose were made innormokalemic dogs, and the effect on the duration ofR-R, Q-T intervals and the amplitude of the T waveswas measured before the appearance of AV block andafter AV block appeared. ST-T segment position andconfiguration were also observed. The plasma K levelswere then elevated by the infusion of a buffered iso-tonic (155 mEq per L) solution of K phosphate in dis-tilled water administered at a rate of 0.5 to 1.0 mEq perminute through a femoral vein catheter. The effect onthe ECGwas evaluated as above with acetylcholine in-jection in these hyperkalemic animals. As a controlstudy, identical experiments were carried out with thesubstitution of isotonic buffered sodium phosphate forthe K solution.

Results

The amount of acetylcholine that was adminis-tered averaged 0.295 mg per 15-second injection,with a range of 0.096 to 0.955 from experimentto experiment. As pointed out in an earlier com-munication, this variation from experiment to ex-periment may have been due, among other factors,to the placement of the catheter in relation to thecoronary ostia resulting in unequal perfusion ofthe two coronary arteries (7, 8).

In 8 of 11 experiments, when the plasma K wasnormal, acetylcholine had a definite effect on theamplitude of the T wave of the ECGwithin 5 to10 seconds after the start of injection and beforethe appearance of AV block (p < 0.01). In theremaining three experiments (274, 275, 276-1),before appearance of AV block no change inheight of T wave was measurable, but a change

1769

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1771ACETYLCHOLINEAND REPOLARIZATION OF THE HEART

TABLE II

Change in amplitude of T wave due to acetylcholine

Difference betweenNormal plasma K (A) Elevated plasma K (B)* A and B

Before AV block During AV block Before AV block During AV block Before DuringExperi- AV AV

meant K Control Change Change K Control Change Change block block

mEq/L mm mm % mm % mEq/L mm Momm ag mm % % S

274 3.5 2.0 0.0 0 0.0 0 5.8 1.0 0.5 50 6.0 600 50 600275 4.2 2.0 0.0 0 1.0 50 5.6 1.0 0.0 0 2.0 200 0 150276 2.4 2.0 1.0 50 5.0 1.5 1.25 117 67276-1 4.1 2.5 0.0 0 0.2 8 7.1 2.3 0.7 30 1.2 52 30 44277 3.6 3.0 1.0 33 3.0 100 8.4 4.0 5.0 125 10.0 250 92 150278 3.7 1.2S 0.5 40 0.75 60 6.8 0.75 0.75 100 1.25 167 60 107278-1 2.7 1.0 0.5 50 0.75 75 7.5 1.25 0.75 60 2.75 220 10 145279 3.0 0.75 0.5 66 5.4 1.0 2.0 200 134281 2.6 3.3 0.3 10 1.0 30 7.3 4.0 2.0 50 6.2 155 40 125282 4.2 0.75 0.25 33 7.8 2.0 3.5 175 142285 4.3 1.5 1.5 100 8.0 2.5 5.5 220 120

Mean 1.82 0.5 34.5 0.96 46 1.94 2.40 102 4.2 235 68 189SD 1.87 :10.49 ±32.0 40.98 ±36 ±1.17 ±2.00 ±73 +3.3 ±173 ±49 4195p <0.01 <0.001 <0.001 <0.05

* Highest plasma K at which acetylcholine induced AV block.

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FIG. 1. THE EFFECT OF ACETYLCHOLINE IN TWO NORMOKALEMICDOGS (EXPERIMENTS276, 285) AND ONE WITH AN ELEVATED PLASMA K (EXPERIMENT 277). The T-wavechanges are independent of the heart rate or alteration of the QRScomplex. The stripsin columns A and B were obtained before and during injection of acetylcholine. Thedose of the drug was 0.30, 0.61, and 0.09 mg in experiments 277, 276, and 285, re-spectively. In experiments 276 and 285, in addition to T-wave changes, the P wavesbecame diphasic, the Ta segment elevated, and the P-R interval prolonged.

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C. FISCH S. B. KNOEBEL, AND H. FEIGENBAUM

in configuration was noted. In all 11 experimentsT-wave amplitude was altered by acetylcholineafter plasma K was elevated (p < 0.001). Thepercentage of change in T-wave amplitude pro-

duced by acetylcholine was greater in all cases

when the animals were hyperkalemic than thatdemonstrated in normokalemic dogs (p < 0.001).The alteration in T wave was independent of bloodpressure and the R-R interval. There was no sig-nificant change in the Q-T interval.

In seven experiments AV block was producedby acetylcholine at both normal and elevatedplasma K levels. The acetylcholine effect on

T-wave amplitude during AV block was also con-

sistently augmented by increased plasma K levels(p < 0.05).

In three experiments acetylcholine injection re-

sulted in a shift of the ST segments. Thesechanges were accentuated by elevation of plasmaK.

The effect of acetylcholine at different K levels

on the heart rate, amplitude of the T waves, Q-Tinterval, and blood pressure for all 11 experi-ments is presented in Tables I and II.

Figure 1 (experiments 277, 276, 285) is an ex-

ample of the effect of acetylcholine on the T wave

in two normokalemic animals (276, 285) and inone in which the plasma K was elevated (277).The strips on the left show the ECGbefore in-jection of acetylcholine. The ones on the rightwere recorded during the injection of acetylcho-line and immediately before the appearance ofAV block. An increase in amplitude of T waves

is noted in all three strips. In addition a pro-

longation of P-R interval is evident. In experi-ments 266 and 285 the P wave became diphasicand the P-Ta segment elevated. No change inshape or duration of QRS nor any measurablechange in the duration of the QT interval was

observed. This figure also demonstrates that theeffect of acetylcholine on the T wave is inde-pendent of the heart rate.

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FIG. 2. CONTINUOUSTRACINGS OF THREE SEPARATE INJECTIONS OF 0.30 MGOF ACETYLCHOLINEAT DIFFERENT PLASMA

LEVELS OF K. The beginning of each strip signifies the onset of injection. Prompt alteration of the T wave is evi-dent, and this alteration is exaggerated by elevating the plasma K. In addition, the effect of acetylcholine on Pand Ta is augmented by raising the plasma K.

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ACETYLCHOLIN'E AN'D REPOLARIZATION OF THE HEART

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1773

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FIG. 3. MOREDETAILED REPRESENTATIONOF THE CHANGESDESCRIBED IN FIGURE 2. Rows A, B, C, and Dare representative of tracings recorded at the start of acetylcholine injection, just before appearance of AVblock, during the AV block, and immediately after disappearance of the block.

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FIG. 4. THE ACCENTUATION OF T-WAVE NEGATIVITY (EXPERIMENT 282) AND ELEVATION OF S-T SEG-MENT (EXPERIMENT 279) AFTER INJECTION OF 0.09 AND 0.12 MGOF ACETYLCHOLINE, RESPECTIVELY. The ef-fect of acetylcholine on the T wave in experiment 282 was accentuated by raising the plasma K to 7.8mEq per L. Similarly the shift of S-T segment in experiment 279 was augmented by elevating theplasma K to 5.5 mEq per L.

I

3

T

C. FISCH S. B. KNOEBEL, AND H. FEIGENBAUM

Figure 2 (experiment 277) shows continuousrecordings during three separate injections of

acetylcholine. The injections were made at plasmaK of 3.6, 8.4, and 6.6 mEq per L, respectively.In addition to the previously described effect ofacetylcholine when the plasma K is normal (toptracing), the augmentation of the acetylcholineeffect on the T wave at an elevated plasma K levelis demonstrated. The accentuation of the T-waveamplitude is evident before and after appearance

of acetylcholine-induced AV block. The heartrate during AV block was the same in all threeinjections. The most marked T-wave change isevident at a plasma K level of 8.4 mEqper L withlesser alterations at a plasma K of 6.6 mEqper L.The alteration of P and Ta segment also is most

pronounced at the higher plasma K level. Thechanges described in Figure 2 are presented ingreater detail in Figure 3, where rows A, B, C,and D are representative sections of tracings re-

corded before acetylcholine injection, just beforethe appearance of AV block, during the AV block,and immediately after disappearance of the block.

In Figure 4 the strips shown in rows A, B, andC were recorded at the start, at the end, and 10seconds after infusion was stopped. Experiment282 shows that with elevation of plasma K to 7.8mEq per L acetylcholine accentuates the biphasicnature of the T wave (row B). Experiment 279is an example of an observation made in 3 of the11 experiments in which acetylcholine, in additionto increasing the height of the T wave, shifted S-Tsegment. This elevation was most striking whenthe plasma K was raised.

Discussion

The data show that acetylcholine when injectedjust above the aortic valves of the normokalemicdog had a measurable effect on the amplitude ofthe T wave of the surface ECGin 8 of 11 experi-ments, and in 3 the configuration of the T wave

changed. The measurement of the T-wave am-

plitude during infusion of acetylcholine is at timesdifficult because of the appearance of Ta segment,a shift of J point, and alteration in contour and

position of ST segment. In each experiment the

effect of acetylcholine on the T wave was aug-

mented by increasing the plasma K level. T-wave

changes may be due either to altered conduction

velocity or to primary change in the duration ofrepolarization. In our experiments the configura-tion and duration of the QRS remained un-changed, and for this reason the alteration inheight and configuration of the T wave is primaryand indicative of accelerated repolarization. Thevariation in magnitude of T-wave change fromexperiment to experiment may be due to an un-even effect of acetylcholine on repolarization ofthe ventricle.

The failure of the QT interval to change in ourexperiments might result from uneven perfusionof the myocardium or, if perfusion were uniform,from an inhomogeneous effect on repolarization(9, 10) of the ventricle. The failure to registerchange of the Q-T interval, on the other hand,may be due to lack of sufficient sensitivity and fineresolution of the recording instrument. It shouldbe noted, however, that the Q-T interval did notincrease despite reduction of the heart rate dueto AV block.

Although the surface ECGdoes not give preciseinformation as to the electrical behavior of thecell, it is the differential quotient of the mono-phasic action potentials of the cardiac fibers (11-13); thus, our results might be assumed to indi-cate an effect of acetylcholine on the mammalianventricle. As suggested by Hecht (13), altera-tion of R-T junction and RS-T segment may berelated to change in the first phase of recoveryand alteration of the T wave to modification of theduration of the slope of the final recovery process(phase 3).

The clear demonstration of the effect of acetyl-choline on repolarization in our experiments isin contrast to observations of previous workers.The discrepancy can perhaps be explained by thetechnique of intracoronary injection in the in-tact animal. The possibility must also be con-

sidered that, in the intact animal, liberation ofother effector substances such as catecholaminesfrom the stores within the heart itself contributedto ST-T changes observed in our experiments(14). It may also be that for an acetylcholineeffect on the action potentials of ventricle to be-come manifest, the proper K environment needsto be present. If acetylcholine affects the re-

polarization phase of the action potential by in-creasing K permeability, the importance of suffi-cient K is implied (15-19).

1774

ACETYLCHOLINEAND REPOLARIZATION OF THE HEART

A discussion of the changes noted in atrial re-polarization in our experiments is not pertinent;they may in part be due to change in atrial con-ductivity as indicated by alteration in appearanceand duration of the P wave.

Summary

Acetylcholine has been shown to alter the re-polarization of the ventricles in the intact dog.This effect is augmented by raising the plasmalevel of potassium.

References1. Burn, J. H., E. M. V. Williams, and J. M. Walker.

The effects of acetylcholine in the heart-lung prep-aration including the production of auricular fibril-lation. J. Physiol. (Lond.) 1955, 128, 277.

2. Loomis, T. A., and S. Krop. Auricular fibrillationinduced and maintained in animals by acetylcholineor vagal stimulation. Circulat. Res. 1955, 3, 390.

3. Cranefield,- P. F., B. F. Hoffman, and A. P. deCarvalho. Effects of acetylcholine on single fibersof the atrioventricular node. Circulat. Res. 1959,7, 19.

4. Hoffman, B. F., and P. F. Cranefield. Electrophysi-ology of the Heart. New York, McGraw-Hill,1960, pp. 56, 86, 277.

5. Rothschuh, K. E. Electrophysiologie des Herzens.Darstelling, Kritie, Probleme. Darmstadt, VerlagDr. 0. Steinkopff, 1952.

6. Hoffman, B. F., and E. E. Suckling. Cardiac cel-lular potentials: effect of vagal stimulation andacetylcholine. Amer. J. Physiol. 1953, 173, 312.

7. Fisch, C., H. Feigenbaum, and J. A. Bowers. Theinhibition of acetylcholine-induced atrioventricularblock by potassium. J. clin. Invest. 1963, 42, 563.

8. James, T. N. Anatomy of the Coronary Arteries,New York, Paul B. Hoeber, 1961, p. 162.

9. Schaefer, H., and H. G. Haas. Handbook of Physi-ology. Circulation. Baltimore, Williams and Wil-kins, 1962, p. 382.

10. Han, J., and G. K. Moe. Nonuniform recovery ofexcitability of ventricular muscle. Circulat. Res.1964, 14, 44.

11. Eyring, H., and R. Parlin. Some molecular aspectsof heart behavior. Ann. N. Y. Acad. Sci. 1957,65, 679.

12. Hecht, H. H. Some observations on theories con-cerning the electrical behavior of heart muscle.Amer. J. Med. 1961, 30, 720.

13. Hecht, H. H. Normal and abnormal transmembranepotentials of the spontaneously beating heart.Ann. N. Y. Acad. Sci. 1957, 65, 700.

14. Hoffmann, F., E. Hoffmann, S. Middleton, and J.Talesnik. The stimulating effect of acetylcholineon the mammalian heart and the liberation of anepinephrine-like substance by the isolated heart.Amer. J. Physiol. 1945, 144, 189.

15. Holland, W. C., C. E. Dunn, and M. E. Greig. Stud-ies on permeability, VIII. Role of acetylcholinemetabolism in the genesis of the electrocardiogram.Amer. J. Physiol. 1952, 170, 339.

16. Hodgkin, A. L., and R. D. Keynes. The potassiumpermeability of a giant nerve fibre. J. Physiol.(Lond.) 1955, 128, 61.

17. Hodgkin, A. L., and P. Horowicz. The influenceof potassium and chloride ions on the membranepotential of single muscle fibres. J. Physiol.(Lond.) 1959, 148, 127.

18. Hutler, 0. F., and D. Noble. Rectifying propertiesof heart muscle. Nature (Lond.) 1960, 188, 495.

19. Harris, E. J., and 0. F. Hutler. The action of acetyl-choline on the movements of potassium ions in thesinus venosus of the heart. J. Physiol. (Lond.)1956, 133, 58.

1775