Electrocardiographic changes in severe hypokalemia

Electrocardiographic

Changes in

Severe Hypokalemia A Reappraisal * GERALD F. FLETCHER, M.D., J. WILLED HURST, M.D., F.A.C.C. and ROBERT C. SCHLANT, XL)., F.:\.c.c. Atlanta,

Georgia

laboratory were checked. =\I1inpatients with serum potassium concentrations of 2.5 mEq./L. or less had 12-lead electrocardiograms taken as soon as possible, usually within two hours and never more than four hours after blood was taken for potasssium determination. Serial 12-lead follow-up electrocardiograms were taken within one hour of the time of repeat serum potassium determination, until correction of the hypokalemia or until death. The frequency of repeat electrocardiograms was determined by the rapidity of potassium replacement and varied from two to three tracings daily for patients receiving intravenous replacement to one tracing every two days in those receiving oral replacement. As noted by Surawicz et. a1.,4 hypokalemic changes when present were usually best seen in lead II and Vs.

A

NUMBER of studies have been reported in the last three decades regarding the electrocardiographic changes associated with hypokalemia. In 1948 Terail’ concluded that the electrocardiogram correlates poorly with the changes in serum potassium, and balance studies by Schwartz and associates2 in 1954 revealed no constant correlation between body potassium and the electrocardiogram. However, because of the few patients studied by Schwartz et al. with serum potassium of less than 3.0 mEq./L., no conclusions on extensive depletion can be made. On the contrary, in 1950 Bellet et ale3 studied 79 patients and concluded that the electrocardiogram was an “important adjunct” in the diagnosis of hypokalemia. Surawicz et a1.4 in 1957 stated that there was a “good correlation between plasma potassium and the and that, unless tachyelectrocardiogram” cardia was present, a “tracing of hypokalemia” would be expected if the serum potassium was less than 2.7 mEq./L. In 17 patients with serum potassium less than 2.7 mEq./L. they found that 78 per cent had electrocardiograms typical of hypokalemia. Weaver and Burchell5 in 1960, in their study of 130 selected patients, also found a definite correlation between the electrocardiogram and the serum potassium. The present study was initiated because of the variable conclusions of the aforementioned investigators and because of the few patients previously studied with extremely low serum potassium (2.5 mEq./L. or less).

RESULTS There were 24 patients with determinations of serum potassium of 2.5 mEq./L. or less. The clinical diagnoses, serum potassium levels, initial serum CO2 content and comments on are listed in Table I. electrocardiograms Examples of electrocardiographic changes are shown in Figures 1 to 3. Two independent experienced observers analyzed the electrocardiograms and classified them into arbitrary groups of severe-classic changes, mild-moderate changes, or no significant change of hypokalemia. The criteria used in grouping the electrocardiograms were similar to those employed by Surawicz and associates4 with regard to S-T segments and In our study, severe-classic changes U waves. involved a U wave of 3 mm. or more in amplitude with loss of the T wave and definite S-T segment depression (1 mm. or more). Mild-moderate changes refer to a U wave of 2 mm. or less in amplitude, a positive T wave

METHOD For a period of six months the reports of all serum electrolyte determinations in the hospital clinical

* From the Department of Medicine, Emory University School of Medicine, and the Medical Service at Grady Memorial Hospital, Atlanta, Ga. 628

THE

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Electrocardiogram

620

in H>-pokalemia

Clinical Data in 24 Patients

(mEq./L.) Final Initial

Initial Serum CO* (mm./L.)

2.1 3.6 4.0 3.9 2.6 2.5 , ? 3.5 3.5 2.6 25 4.0 4.0 3.9 4.6 38 3.9 4.5 3.4 5.0 3.1 3.6 3.7

40.0 19.1 44.0 22.0 7 15.0 34.0 36.5 19.3 26.2 33.7 14.5 24.8 22.0 33.0 34.5 28.5 23.5 32.5 17.5 23.0 26.0 23.5 34 0

Serum (bSC No.

Diagnosis

K*

Treatmentt

EtxG Chaners

with Potassilrm (mEq./24 hr.)

Cl~loridc

Alcoholism-diarrhea Cirrhosis-alcoholism Cirrhosis-alcoholism Cirrhosis-alcoholism Thiazide diuresis-pregnancy Cirrhosis-alcoholism Water intoxication (psychotic) Sclrrodermaliarrhea Alcoholism Gantritis-vomiting Cirrhosis-alcoholism Chronic pyelonephritis; sepsis Hyprremesis gravidarum Hyperemesis gravidarum Diarrhea Diarrhea-alcoholism Pancreatitis-vomiting Diarrhea Hypercmeris gravidarum Cirrhosis-alcoholism Pneumococcal meningitis Cirrhosis-alcoholism Lobar pneumonia; hypertension Cirrhosis-alroholism

4

15 16 17 18 19 20 211 225. 23 24

1.6 1.8 1.8 1.8 1.8 1.9 2.0 2.0 2.0 2.0 2.0 2.2 2.2 2.3 2.3 2.3 2.3 2.3 2.4 2.4 2.4 2.4 2.5 2.5

S.-C. &1.-X1. M-M. M.~Sl. M-hf. M-M. M.-hi. M.-%I. S.-C S.-C. M-M. M-M. N.-C:. xi.-!vl. XL-M, S.-C. M-M. N.-C. \GM. S.-C. N.-C. Sf.-M. .\I.-MM. 11.-M.

* Normal wrum potassium = 3.5-5.5 mEq./L. t Patients able to eat were on either a regular diet or a 2 gm. sodium diet (cirrhotic patients) potassium/24 hr. $ Patient died. ECC. = electrocardiographic; S.-C. severe-classic; I.V. = intravenously; P.O. = per 01;

1 I

10-25-65

“3

fl2.6

10-25-65 (2hrs later)

10-26-65

10-27-65

FIG. 1. Patient 20. Example of electrocardiogram with “severe-classic” changes. This patient received 50 mEq. of potassium chloride between Oct. 25 to 27, 1965. Note the obvious S-T segment changes and the 3 mm. U wave in Vs in the October 25 strips. (The variation in R wave height in serial recordings probably represents variation in electrode placement.) VOLUME

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180 1.V. for 1 day 45 P.O. for I3 days + diet 100 I.V. for 3 days, then 110 P.O. l-or IO days f dirt 40 I.V. for 1 day, then 32 P.O. for 5 days + dirt 60 P-0. for 6 davs + diet 30 P.O. for 3 days + dkt No follow-up NO”SE 80 I.V. simultaneously with 40 P.O. for 2 days 40 I.V. for 1 dav, then 20 P.O. for 8 days 40 I.V. & 50 P.O. simultaneously for 2 days NO”C 20 I.V. for 1 day + diet 80 I.V. fox 1 dav + dirt 50 P-0. for 8 days f dirt 140 I.V. for 1 day, then 45 P.O. for 8 days f diet 45 P.O. for 8 days 25 P.O. for 10 days 20 I.V. for 3 days 25 I.V. for 2 days 60 I.V. for 1 day 20 P.O. for 3 days + diet Diet onlv for 5 days 80 I.V. for 1 day, thrn diet

,

;

both diets contained

N.C.

z

no change;

approximately

M.-M.

50-150

mEq.

of

= mild-moderate.

which is smaller than the U wave and only slight S-T segment depression (less than 1 mm.). No change refers to only slight distortion of the T wave without obvious S-T segment or U wave changes. Of the 24 patients only 5 (20.8y0) had severeclassic changes of hypokalemia, whereas 16 There (66.7%) had mild-moderate changes. were only 3 patients (12.5y0) whose electrocardiogram revealed no significant change of hypokalemia. Within the group of 21 patients (87.5%) with the severe-classic or mild-moderate electro-

12-g-65

FIG. 2. Patient 17. Example of electrocardiogram with “mild-moderate” changes. This patient received 225 mEq. of potassium chloride between Dec. 9 and Dec. 14,1965. Note the 2 mm. wave and the slight S-T segment changes in the December 9 strips.

630

Fletcher, II

10-29-65

Hurst

v3

FIG. 3. Patient 18. Example of electrocardiogram with “no change,” despite a serum K+ of 2.3. This patient received 250 mEq. of potassium chloride between Oct. 29 and Nov. 11, 1965. Note the slight distortion of the T wave without obvious S-T segment or U wave changes.

cardiographic changes of hypokalemia there was, however, no apparent correlation between the severity of these changes and the degree of hypokalemia in each patient. However, in the 3 patients (12.5%) with no change, the hypokalemia was less severe (2.2-2.4 mEq./L.). The relation between electrocardiographic changes and serum potassium level for all the patients is illustrated in Figure 4. DISCUSSION

In this study of 24 highly selected patients with hypokalemia (serum potassium of 2.5 mEq./L. or less) the over-all correlation between serum potassium concentration and electrocardiographic changes is somewhat in contrast to the findings of Terail’ and Schwartz et a1.,2 who believed that the electrocardiogram correlates poorly with the serum potassium; they No chanae

Mild-Moderate

Severe-Classical

*+ *+

“+++

1.7

1.6

+

and

Schlant

are similar to the results of Bellet et a1.,3 Surawicz et al.4 and Weaver and Burchell,s who reported a good correlation between the electrocardiogram and serum potassium. However, the lack of individual correlation between the serum potassium level and the severity of electrocardiographic changes indicates that the electrocardiogram does not always provide an accurate indication of the exact level of the serum potassium once it is below 2.5 mEq./L.; for example, Patient 20 had severe-classic electrocardiographic changes with a serum potassium of 2.4 mEq./L., whereas Patient 2 had only mildmoderate changes with a serum potassium of 1.8 mEq./L. It is possible that the increased frequency of potassium determinations in recent years increases the likelihood of finding more instances of severe hypokalemia. This, especially in our patients, led to obtaining electrocardiograms that might otherwise not have been obtained. In addition, in our 11 cirrhotic patients the severe potassium depletion was probably chronic, thus allowing time for systemic compensation to occur and possibly resulting in fewer electrocardiographic changes. It is noteworthy that 6 of 24 patients died; only 1 (Case 23) had known heart disease, and only 1 (Case 1) had an arrhythmia. In all of the patients generalized muscular weakness was on the average more frequent and more marked than depression of deep tendon reflexes. In view of innumerable factors, including acidosis, alkalosis and numerous mineral ions6 which contribute to changes in the electrocardiogram, it is actually not surprising that a single factor, low serum potassium, was found to correlate poorly with the electrocardiogram in individual patients. In the 24 patients reported there was also no definite correlation between the degree of electrocardiographic evidence of hypokalemia and the serum CO2 content. Ultimately it is hoped that, with greater knowledge of the complex interrelations among the major electrolytes affecting the electrocardiogram, a better prediction of serum concentrations can be obtained from an analysis of the electrocardiogram.

*

FIG. 4. Serum potassium levels in mEq./L. (ordinate) plotted with electrocardiographic changes (no change, mild-moderate, severe-classic) as graded by Observers 1 (*) and 2 ( +).

SUMMARY

Electrocardiograms were recorded in 24 patients with serum potassium of 2.5 mEq./L. or less. Only 5 (20.8%) had severe-classic changes of hypokalemia. Sixteen (66.7%) had mildmoderate changes and 3 (12.5%) had no THE

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OF CARDIOLOGY

Electrocardiogram chmges. It is concluded that, although most (21 of 24, or 8’7.5%) of these patients had at least some definite electrocardiographic changes, in individual patients there is poor correlation between the severity of the hypokalemia and the electrocardiographic abnormalities. When changes were present, however, they were clinically helpful and evolved as expected during potassium replacement. REFERENCES 1. TERAIL, R. Relation of abnormalities in concentration of serum potassium to electrocardiographic disturbances. Am. J. Med., 5: 828, 1948.

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2. SCHWARIZ, W. B., LEVINE, H. I>. and KELMAN, A. S. ‘The electrocardiogram in potassimn depletion: Its relation to the total potassium deficit and the serum concentration. r4m. J. Med., 16: 395, 1954. 3. BELLET, S., STEIGER, W. A., NADLER, C. S., and GAZES, P. C. Electrocardiographic patterns in hypopotassemia. Observations in 79 patients. .Im. J. M. SC., 219: 542, 1950. 4. SURAWICZ, B. ET AL. Quantitative analysis of the electrocardiographic pattern of hypopotassemia. Circulation, 16: 750, 1957. 5. \VEAVER, W. F. and BURCHELL, H. II.: Serum potassium and the electrocardiogram in hypokalemia. Circulation, 21 : 505,196O. 6. LEPESCHKIN, E. Modern Electrocardiography, Vol. 1, p. 282. Baltimore, 1951. Williams & Wilkins