THE ELECTROCARDIOGRAM OF · this time the serum potassium remained at an abnormally low level...

THE ELECTROCARDIOGRAM ASSOCIATED WITH LOW LEVELSOF SERUM POTASSIUM

BY

P. M. McALLENFrom the West Middlesex Hospital

Received May 7, 1950

In recent years it has become increasingly evident that a depletion of body potassium may occurin a number of conditions. The relationship of a fall in the serum potassium to the attacks of-familial periodic paralysis is well known. Potassium deficiency has also been found in infantilediarrhoea, intestinal obstruction with vomiting, sprue, renal insufficiency, diabetic coma, Addison'sdisease with overdosage of desoxycorticosterone acetate, and in patients in whom the potassiumintake has been low over a long period. Abnormalities in the electrocardiogram have been reportedin each of the above conditions when the serum potassium has been at a low level. Theseabnormalities have been found mainly in the S-T segment, the T wave, and the Q-T interval.Electrocardiograms of three cases with low serum potassium are presented in this paper; in two ofthem it remained low over long periods and many tracings were obtained,

PROCEDURE

All the serum potassium estimations were made by a modification of the method of Kramer andTisdall(Jacobs and Hoffman, 193 1)using a photo-electric absorptiometer for-evaluationof the colour.Special precautions were taken to prevent hlmolysis on withdrawal of the blood and the serum wasremoved within two hours of collection. The accuracy of the method, using duplicate estimations,was found to be ±0 5 mg. per 100 ml. Normal values by this method lie between 16 and 20 mg.per 100 ml. of serum.

'Electrocardiograph leads I, II, III, Vi, V3, and V5 were used. All tracings were taken with thepatient recumbent. Care was taken to exclude, as far as possible, factors other than potassiumthat might influence the S-T segment or the T wave. In no case was there evidence of coronarydisease, preponderance of a ventricle, paroxysmal tachycardia, severe anmmia, myxcedema, tetany,or trauma to the chest wall. No digitalis or other significant drugs had been given. In all tracings,the Q-T interval measurement was corrected for the heart rate using Bazett's formula as expressed

by Taran and Szilagyi (1947) where K= vQC [C=cycle length; K=the corrected Q-T interval].On every occasion, the electrocardiogram and the blood sample were taken simultaneously.

This was considered essential as the serum potassium level is known to vary from hour to hour,especially when the patient is being given potassium salts (Wilkins and Kramer, 1923; Sampsonet al, 1943). Forty-four cardiograms corresponding to various levels of serum potassium werestudied in the three cases.

CASE REPORTSCase 1. Woman, aged 41 years. A typical case of idiopathic steatorrhcea admitted during

an acute phase of the disease. The patient was thin and poorly developed. The tongue wassmooth and there were fissures at the angles of the mouth but there were no other abnormalphysical signs. The blood pressure was 105/80. Radiological examination showed a normal,

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160 P. M. McALLEN

small heart and clear lung fields. Blood chemistry values per 100 ml. of serum were: sodium317 mg., potassium 10-4 mg., calcium 9-2 mg., and chlorides (as sodium chloride) 654 mg.

The patient's serum potassium remained low for the first three months under observation.Subsequently, as her condition improved, the level rose to 20-6 mg. per 100 ml. The bloodchemistry was otherwise always normal. With the alterations in the serum potassium there was atno time any significant change in the state of the cardiovascular system'.

Electrocardiograms. During the whole period of observation a series of cardiograms wastaken which covered a range of serum potassium levels from 20-6 mg. to 12-1 mg. per 100 ml.(Fig. 1). In this series, all tracings taken at levels above 18-3 mg. per 100-ml. are normal, whereas,at and below this level they show an abnormally flat or inverted T wave and sometimes a depressed

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FIG. 1.-Case 1. Tracings at different levels of serum potassium: (A) Normal tracings. The Q-Tc is 0-411 sec.As the serum potassium falls (B) the T wave becomes abnormally flat in leads I and II, and inverted in III, V3and V5. The Q-Tc is 0-400 sec. (C) The T wave is now also inverted in lead II and the S-T segment is slightlydepressed in V5. The Q-Tc is 0 400 sec. (D) The abnormalities in the T wave and the S-T segment are moremarked. Normal U waves are now visible in most leads. The Q-Tc is 0 402 sec.

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ELECTROCARDIOGRAM WITH LOW SERUM POTASSIUM

S-T segment.. Both the degree of the abnormalities and the number of leads in which they areseen, increase in proportion to the fall of the serum potassium; The electrocardiograms are normalin all other respects.

The corrected Q-T interval has a range from 0402 to 0-426 sec. The slight variations in theQ-T interval are unrelated to the level of the serum potassium. Abnormalities are present in theelectrocardiograms of this case even when the serum potassium is within the usually accepted limitsof normal. The abnormalities in the electrocardiogram could be corrected temporarily by givingpotassium chloride intravenously (Fig. 2).

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FIG. 2.-Case 1. The effect of intravenous potassium chloride on the electrocardiogram; 10 g. of potassium chloridewere given over a period of two hours. (A) Before potassium. The S-T segment is depressed in leads II, IIIand V5; the T wave is flat in leads I and V5, and inverted in V3. (B) At the end of the two hours of intravenouspotassium. The abnormalities have been corrected. (C) Seventy-two hours after (B); the T wave is againflat in lead I and inverted in V3 and V5.

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P. M. McALLEN

Case 2. Woman, aged 39 years. A known case of ulcerative colitis of three years durationwho was admitted to hospital during an exacerbation of her disease. The patient was thin but therewere no abnormal physical signs in any system. The blood ptessure was 120/70. Radiologicalexamination of the heart and lungs was normal. The blood chemistry values per 100 ml. of serumwere: sodium 311 mg., potassium 16-1 mg., chlorides (as sodium chloride) 555 mg., calcium 8'4 mg.,and phosphorus 4-6 mg. Two subsequent serum potassium determinations showed levels of12-9 and 18-0 mg. per 100 ml.

Electrocardiograms (Fig. 3). As the serum potassium level falls there is some decrease in theamplitude of the T wave in the chest leads. However, the T wave and all other parts of the tracingare within normal limits. The duration of the corrected Q-T interval is almost constant throughout.

Case 3. Woman, aged 45 years. A case of ulcerative colitis ofmore than twenty years duration.The right kidney had been removed for an abscess ten years previously. She was admitted becauseof increasing severity of her bowel condition. The patient was thin, but there were no abnormalphysical signs to be found in any system. The blood pressure wts 10/70. An X-ray of the chestshowed a normal, small heart and clear lung fields. The renal futiction tests were normal. Bloodchemistry values per 100 ml. of serum were: sodium 304 mg., potassium 11 1 mg., chlorides (assodium chloride) 590 mg., calcium 116 mg., and phosphorus 3-7 mg. Subsequent determinationsshowed no significant change from normal other than in the serum potassium.

The diarrhoea was unremitting for the next twelve months and during this time the patient wasliable to attacks of severe muscular weakness which coincided with vory low serum potassium levels.These attacks were relieved by giving potassium chloride by mouth. Throughout the whole ofthis time the serum potassium remained at an abnormally low level unless the patient was givenpotassium.

Electrocardiograms. A series of cardiograms was obtained on this patient at 27 differentlevels of the serum potassium. The range was from 21-0 to 6-3 mg. per 100 ml. (Fig 4 and 5).In this series, all tracings at levels above 11-9 mg. per 100 ml. are within normal limits. At andbelow this level they show a depressed S-T segment, an abnormally low or inverted T wave and alarge U wave (Fig. 4C). Both the degree of the abnormalities and the number of leads in whichthey are present, increase in proportion to the fall of the serum potassium. At the lowest serumpotassium levels, a characteristic undulating tracing is produced by the deep depression of the S-Tsegment, the flat or inverted T wave, and the grossly high and wide U wave (Fig. 5).

In some of the tracings at the lowest serum potassium levels, the height of the P wave in lead IIis greater than 2-5 mm. and the duration of the QRS complex is at the upper limit of normal. Thecorrected Q-T interval has a range from 0-402 to 0-442 sec. Its variations are unrelated to the levelof the serum potassium. It is of interest to follow the changes that occur in the T wave and theU wave as the serum potassium falls. These changes are most clearly seen in lead V3 (Fig. 6).The T wave steadily decreases in amplitude, becomes flat and then inverted. Concurrently, theU wave increases in height and width and encroaches upon the T wave. Difficulty may arise in theinterpretation of the tracing when the T wave is flat and the U wave is high. Here, the U wavemay easily be mistaken for an upright T wave associated with a prolonged Q-T interval (Fig. 5and 6). The true nature of this U wave is usually revealed by the presence of an upright or invertedT wave preceding it in one of the other leads (Fig. 5).

It was found that all the abnormalities in the cardiogram could be corrected within one hourby the administration of 7 5 g. of potassium chloride by mouth. Four hours after this dose thecardiogram reverted to its previous state.

COMMENTEach of the three cases reported has a different response to a fall in the serum potassium as

shown in the electrocardiogram. This is well seen at levels in the region of 12 mg. per 100 ml.In Case 1, S-T segment depression and T wave inversion occur. In Case 2, there is lowering of the

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FIG. 4.-Case 3. Tracings at different levels of serum potassium. (A) Normal tracings. Q-Tc is 0 400 sec.(B) Normal tracings, but there are some changes in the amplitude of the T wave and the U wave. The Q-Tcis 0-420 sec. (C) In leads II, HI, V3 and V5, the T wave is oflow amplitude and the U wave is large. In lead IHand V5 there is slight S-T segment depression. The Q-Tc is 0-416 sec. (D) In leads III, V3, and V5 the T wavehas become inverted. The abnormalities in the S-T segment and the U wave are greater. The Q-Tc is 0-400sec.

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T wave voltage only. In Case 3, a depressed S-Tsegment is combined with a low T wave and alarge U wave. Further, in Cases 1 and 3, thereis a marked difference in the level to which'thepotassium fealls before the electrocardiogram be-comes abnormal (18-3 and 11[9 mg. per 100 ml.respectively).

In Case 3, when the serum potassium is lo.w,there is an abnormal increase in the amplitude ofthe P wave. This is in contrast to the flatteningor disappearance of the P wave which is known tobe associated with a high level of serum potassium.In none of the three cases is there lengthening ofthe Q-T interval with a fall in the serum potas-sium.

PREVIOUSLY REPORTED CASES

LOW SERUM POTASSIUM 165

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Electrocardiograms associated with low ser'um -4-potassium levels have been presented in reportson familial periodic paralysis (Stewart et al., 1940;Stoll and Nisnewitz, 1941; Gass et al., 1948;iPerelson and Cosby, 1949), infantile diarrhoea -(Gamble et al., 1948), intestinal obstruction (Bellet.....et al., 1949), sprue (Engel et al., 1949), renal insuffi- --1ciency (Brown et al., 1944; Tarail, 1948), diabetic - ~

Nadler et al., 1948; Ernstene and Proudfit, 1949), FAddison's disease (Thompson, 1939; Currens andWhite, 1944; Ernstene and Proudfit, 1949), and -I I ~ Avarious conditions with a low potassium intake(Tarail, 1949).

In most reported cases, the period of low serum. I1potassium was brief and few electrocardiograms 1J -4 -could be obtained. In a number of cases the Js:..I..cardiogram and serum potassium recording werenot simultaneous, being separated sometimes byas long as 24 hours. It is therefore difficultoestablish the potassium level at which abnormali-ties appear in the electrocardiogram, and also to FIG. 5.--Case 3. The electrocardiogram at a serum

potassium level of 10-3 mg. per 100 ml. Inappreciate the progression of these abnormalities leads II, III, V3 and V5, the S-T segment is de-asthelevelfalls. ~~~~~~~~pressed,~the T wave is flat or inverted, and theIn a number of reports, where the Q-T interval U wave is abnormially high and wide. Lead VI

clearly shows an inv-erted T wave and an uprightis said to be prolonged (Stewart et a!., Ernstene U wave. In lead LIIthe height of the P wave isandPoudft,Prelsn andCosb, an Engl et more than 2-5 mm. The duration of the QRS

aL.), broad and deformed T waves are described,. ope s ~0scThese waves are similar in form and position to the U waves of Case 3 in this paper, and they arepart of a similar u1ndulating outline. That these broad waves are in fact U waves is confirmed bythe presence of preceding small T waves in some of the leads. It is considered, therefore, that theQ-T interval has been over-estimated by these authors and is actually within normal limits in mostof their cases. The only reported case with a high voltage P wave at low levels of potassium wasCase 6 of Ernstene and Proudfit.



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FIG. 6.-Case 3. Lead V3 showing the change in the T wave and the U wave as the serum potassium falls. TheT wave decreases in amplitude and eventually becomes inverted; at the same time the U wave increases inamplitude and width. At 10-3 mg. per 100 ml. the U wave simulates an upright T wave associated with a pro-longed Q-T interval.

SUMMARY AND CONCLUSIONSThe abnormalities in the electrocardiogram associated with low serum potassium were studied in

three cases. A different type of tracing was found in each case. The level of serum potassium atwhich abnormalities first appeared was determined in two of the cases.

On examination of the tracings of these cases and of those previously reported, it is found thata lowering of the serum potassium may result in changes in almost any part of the electrocardiogram.Decrease in the amplitude of the T wave is constant and may proceed to inversion. Depressionof the S-T segment is frequent. Marked increase in the size of the U wave occurs in less than halfof the cases. Lengthening of any part of the eleQtrical cycle may occur. High voltage of the P,wave may be present occasionally.

The above abnormalities may be combined in various ways. In most cases, the resultant tracinghas no characteristic form. In some cases it has an undulating outline produced by a depressedS-T segment, a low or inverted T wave, and a high and wide U wave. TbAis outline is,stronglysuggestive of low serum potassium and may prove to be diagnostic. No one type of tracing wasfound to be constantly associated with any one causative disease or condition.

It is considered, contrary to most previous reports, that a prolongation of the Q-T interval isnot commonly associated with a fall in the serum potassium.

I wish to thank Dr. N. F. Coghill for permission to study his cases and for his encouragement in the preparationof this paper. I am indebted to Dr. M. Lubran for much helpful criticism. I also wish to thank Mr. R. J. Hall forthe many biochemical estimations, and the staff of the Electrocardiographic Department for their kind co-operation.

REFERENCESBellet, S., Nadler, C. S., Gazes, P. C., and Lanning, M. (1949). Gastroenterology, 12,49.Brown, M. R., Currens, J. H., and Marchand, J. F. (1944). J. Amer. med. Assoc., 124, 545.Currens, J. H., and White, P. D. (1944). Amer. Heart J., 28, 611.Engel, F. L., Martin, S. P., and Taylor, H. (1949). Bull. Johns Hopkins Hosp., 84, 285.Emstene, A. C., and Proudfit, W. L. (1949). Amer. Heart J., 38, 260.Gass, H., Cherkasky, M., and Savitsky, N. (1948). Medicine, Baltimore, 27, 105.Gamble, A. H., Wiese, H. F., and Hansen, A. E. (1948). Pediatrics, Springfield, 1, 58.Holler, J. W. (1946). J. Amer. med. Assoc., 131, 1186.Jacobs, H. R. D., and Hoffman, W. S. (1931). J.biol. Chem., 93, 685.Martin, H. E., and Wertman, M. (1947). Amer. Heart J., 34, 646.Nadler, C. S., Bellet, S., and Lanning, M. (1948). Amer. J. Med., 5, 838.Perelson, H. N., and Cosby, R. S. (1949). Amer. Heart J., 37, 1126.Sampson, J. J., Alberton, E. C., and Kondo, B. (1943). Ibid., 26, 164.Stewart, H. J., Smith, J. J., and Milhorat, A. T. (1940). Amer. J. med. Sci., 199. 789.Stoll, B., and Nisnewitz, S. (1941). Arch. intern. Med., 67, 755.Tarail, R. (1948). Amer. J. Med., 5, 828.Taran, L. M., and Szilagyi, N. (1947). Amer. Heart J., 33, 14.Thompson, W. A. R. (1939). Lancet, 1, 808.Wilkins, L., and Kramer,B. (1923). Arch. intern. Med., 31, 916.

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