Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2818_Библиотеки_им_академика_М_И_Перельмана
.pdf
290
II
25 mm/s. 10 mm = 1 mV
https://t.me/med1917
22 ECG inElectrolyte Imbalance
22.1.1 Hyperkalaemia
The normal range of serum potassium is between 3.5 and 5.5mEq/L.A departure
from this narrow range can have signicant changes in ECG.Hyperkalaemia (serum
potassium more than 5.5mEq/L) increases cell membrane excitability. The ECG
changes are frequently seen when the serum potassium level is more than
6mEq/L.The typical progressive ECG changes of hyperkalaemia are:
• Peaked, tall and tented T wave
• Gradual decrease and disappearance of P wave
• Widening of QRS complex
• Virtual disappearance of S-T segment
• Atrioventricular conduction defect
• Cardiac arrhythmias
22.1.1.1 Peaked, Tall andTented T Waves
The earliest ECG manifestation of hyperkalaemia is peaked, tall and tented T wave
best seen in the chest leads. At rst the T wave becomes tall and then becomes
slightly wide. This is called ‘tented’ T wave. This is seen when serum potassium is
between 6 and 7mEq/L.Similar picture may also be seen in normal individuals and
posterior wall infarction. The proximal limb is usually steep but the distal limb of
the T wave has more gradual descent (Figs. 22.1, 22.2, 22.3, 22.4, 22.5, 22.6
and 22.7).
I
II
I
Fig. 22.1 ECG showing hyperkalaemia. This is ECG of a 50-year-old gentleman suffering from
Addison’s disease who presented with hyperkalaemia. This is the ECG at the time of presentation.
Note the wide QRS complexes and disappearance of P wave
aVR
aVL
aVF
V1
V2
V3
V4
V5
V6
II
25 mm/s. 10 mm = 1 mV
25 mm/s. 10 mm = 1 mV
25 mm/s. 10 mm = 1mV
22.1 ECG inPotassium Imbalance
https://t.me/med1917
291
I
II
I
aVR
aVL
aVF
V1
V2
V3
V4
V5
V6
Fig. 22.2 ECG showing hyperkalaemia. This is the ECG of the same patient after 10min. Note
the wide QRS complexes and tall T waves. At this time, the serum potassium was 9.1mEq/L.Injection
calcium gluconate was administered and insulin glucose drip was started
I
II
III
aVR
aVL
aVF
V1
V2
V3
V4
V5
V6
Fig. 22.3 ECG showing hyperkalaemia. This is the ECG of the same patient after calcium and
insulin glucose therapy. Note the narrowing of the complexes with treatment. Also note the bundle
branch block appearance in lead V2
I
II
III
Fig. 22.4 ECG of the same patient after correction of serum potassium
Fig. 22.5 Hyperkalaemia
showing sine wave
conguration of QRS
complex
aVR
aVL
aVF
V1
V2
V3
V4
V5
V6
Lead VI
292
Widened QRS complex
Normal
potassium
level
Mild
hyperkalaemia
Severe
hyperkalaemia
abc
https://t.me/med1917
22 ECG inElectrolyte Imbalance
Tall peaked
T wave
Loss of
P wave
with tall T wave (sine
wave configuration)
Fig. 22.6 Diagram showing progressive hyperkalaemia
Fig. 22.7 Diagram
showing progressive
hyperkalaemia. (a) Normal
complex. (b) Raised serum
potassium. Note the tall
and peaked T wave with
blunting of the P wave. (c)
With further rise in serum
potassium, there is
widening of the QRS
complex with peaked T
wave and disappearance of
the P wave
22.1 ECG inPotassium Imbalance
https://t.me/med1917
293
22.1.1.2 Gradual Decrease andThen Disappearance ofP Wave
With further rise in serum potassium level (7–8mEq/L), there is further increase in
height on T wave. The P wave rst decreases in amplitude and then disappears. The
prolongation of P-R interval may precede the disappearance of P wave.
22.1.1.3 Widening ofQRS Complex
The QRS complex becomes wide and bizarre in shape when the serum potassium
lies between 8 and 9mEq/L.This mainly affects the terminal deection. This conduction disturbance resembles bundle branch block. There is further peaking of T
waves. S-T segment depression starts.
22.1.1.4 Virtual Disappearance ofS-T Segment
With rise in serum potassium level (more than 9mEq/L), the S-T segment virtually
disappears as if the proximal limb is incorporated in the ascending limb of T wave.
The QRS complex continues to widen and eventually blends with the T wave, producing the classic sine-wave ECG.
22.1.1.5 Atrioventricular Conduction Defect
Atrioventricular conduction defects are observed in patients suffering from severe
hyperkalaemia. In the initial phase, P-R interval prolongation and QRS widening
are seen but later the sequential changes include atrioventricular junctional delay,
followed by acceleration of junctional pacemakers, conduction delays in the HisPurkinje system and delays in ventricular muscle. Fascicular blocks and bundle
branch blocks are also seen.
294
https://t.me/med1917
22.1.1.6 Cardiac Arrhythmias
Sinus tachycardia and bradycardia, idioventricular rhythm, ventricular tachycardia,
ventricular brillation have all been observed in ECG of patients suffering from
hyperkalemia. Asystole may develop if urgent steps are not taken to manage life
threatening hyperkalaemia.
22 ECG inElectrolyte Imbalance
22.1.2 Hypokalaemia
Hypokalaemia (serum potassium less than 3.5mEq/L) is commonly seen in patients
receiving diuretics, prolonged intravenous uid therapy, vomiting and diarrhoea. It
causes delayed ventricular repolarization shortened refractory period and increased
automaticity. The gradual fall in serum potassium level is reected electrocardiographically by the following features:
22.1.2.1 Gradual Decrease andThen Disappearance ofT Wave
The earliest ECG change of hypokalaemia is decrease in the amplitude of T wave.
The T wave gradually becomes at and then disappears. Later it may be seen as a
small hump on the S-T segment.
22.1.2.2 Presence ofProminent U Waves, Best Seen inLeads V2–V4
With fall in serum potassium, the U wave becomes prominent. When the height of
U wave is more than that of T wave, the serum potassium level is below
3mEq/L.When the T wave has disappeared, the U wave may give a false impression of T wave. Thus, it may also lead to an appearance of pseudo-prolonged Q-T
interval, which is basically Q-U interval. The U wave maintains its round shape
(Figs.22.8, 22.9 and 22.10).
22.1.2.3 Slight Depression ofS-T Segment
There may be S-T segment depression in all the leads.
22.1.2.4 Increase inP-R Interval
The P-R interval gradually increases along with increase in amplitude of P wave and
the P wave falls almost on the preceding U wave. Wenckebach type of seconddegree block is usually seen with very low level of serum potassium.
ab c
UU
22.1 ECG inPotassium Imbalance
https://t.me/med1917
295
U
25 mm/s. 10 mm = 1 mV
Lead II
U
Fig. 22.8 Hypokalaemia
I
aVF
V4
II
V1
V5
25 mm/s. 10 mm = 1 mV
III
V2
aVR aVL
V3
V6
Fig. 22.9 Hypokalaemia. This ECG was taken from a patient suffering from hypokalaemic periodic paralysis. Note the prominent U waves (arrows) in leads V2, V3 and V4
Fig. 22.10 Diagram showing progressive changes in hypokalaemia. (a) Normal complex. (b)
Hypokalaemia. Note the prominence of U wave, which is taller than the T wave. The P-R interval
is prolonged. (c) With further fall in serum potassium, the U wave becomes very prominent with
disappearance of the T wave. Note the further prolongation of the P-R interval
T
U
U
T
U
296
https://t.me/med1917
22.1.2.5 Arrhythmias
Severe hypokalaemia can cause arrhythmias including ventricular tachycardia and
Torsades de Pointes. It also may cause ventricular brillation and sudden cardiac death.
Tips and Tricks
• Look for tall and tented T waves to diagnose hyperkalaemia.
• Look for U waves which are preferably taller than T waves to diagnose hypokalaemia.
• Always remember that tall T waves and prominent U waves are seen in normal
persons as well.
• If you nd tall T waves, keep in mind the possibility of hyperacute myocardial
infarction.
22 ECG inElectrolyte Imbalance
22.2 ECG inCalcium Imbalance
Calcium imbalance is seen in patients suffering from renal failure, disorder of parathyroid glands, pancreatitis and malignancy. Calcium ion is mainly responsible for
phase 2 of action potential when calcium ions enter into the cardiac cells. Calcium
imbalance mainly produces changes in the duration of S-T segment with practically
no changes in QRS complex or T waves.
22.2.1 Hypercalcaemia
The normal serum calcium level is 9–10.5 mg/dL. The ECG changes usually appear
when the serum calcium level is more than 12mg/dL.The most characteristic ECG
change is shortening of Q-T interval and the shortening is due to shortening of the
S-T segment. This occurs due to the shortening of the phase 2 of action potential.
The S-T segment virtually disappears and gets incorporated in the T wave as if it
forms the proximal limb of T wave (Figs.22.11 and 22.12). There may be P-R
Fig. 22.11
Hypercalcaemia
25 mm/s. 10 mm = 1 mV
V1 V2
V3
V4
V5 V6
22.2 ECG inCalcium Imbalance
https://t.me/med1917
297
25 mm/s. 10 mm = 1 mV
I III
25 mm/s. 10 mm = 1 mV
Fig. 22.12 Hypercalcaemia. Note the shortened Q-T interval
II
aVR aVL aVF
interval prolongation and increased duration of QRS interval also. J point elevation
has also been observed in hypercalcaemia.
Additional ECG manifestations in severe hypercalcaemia include S-T segment
elevation, biphasic T waves and prominent U waves.
22.2.2 Hypocalcaemia
Hypocalcaemia occurs when the serum level of calcium is below the lower limit of
normal. The most characteristic ECG change is prolongation of Q-T interval. The
increase in Q-T interval is due to increase in the S-T segment, which is due to prolongation of phase 2 of action potential. The prolongation of Q-T interval is proportional to degree of hypocalcaemia. However the S-T segment is not displaced. The
Q-T interval may be in the region of 0.5–0.6s (Fig.22.13).
298
25 mm/s. 10 mm = 1 mV
https://t.me/med1917
Fig. 22.13 Hypocalcaemia
Lead II
22 ECG inElectrolyte Imbalance
Rarely, there may be decreased T wave amplitude, T wave attening, terminal T
wave inversion or deep T wave inversion in severe hypocalcaemia. In certain
patients, S-T segment elevation mimicking acute myocardial infarction has also
been observed.
Tips and Tricks
• To diagnose hypercalcaemia, look for shortened Q-T interval.
• To diagnose hypocalcaemia, look for prolonged Q-T interval.
• If Q-T interval is prolonged beyond 0.48s, keep in mind the possibility of devel-
opment of Torsades de pointes.
22.3 Magnesium Effect
Usually, the serum potassium and magnesium go hand in hand and the ECG changes
are also similar. The ECG changes of hypomagnesaemia resemble that of hypokalaemia. The U wave increases in amplitude, and the T wave becomes attened. The
S-T segment may be depressed.
The ECG changes of hypermagnesaemia resemble that of hyperkalaemia. There
may be widening of QRS complex and increase of P-R interval.
Self-Assessment Questions
1. Hyperkalaemia can cause a at or absent P wave on the ECG.True or false?
2. Hyperkalaemia can cause a wide QRS complex and peaked T waves on the
ECG.True or false?
3. Hypercalcaemia can cause a shortened Q-T interval on the ECG.True or false?
4. S-T segment is isoelectric in hypercalcaemia. True or false?
5. ECG changes of hypomagnesaemia resemble that of hyperkalaemia. True
or false?
22.3 Magnesium Effect
https://t.me/med1917
299
6. Electrolyte disturbances can cause major changes in the:
a. QRS complex b. P-R interval c. T wave d. All of the above
7. Hypokalaemia is associated with:
a. Prominent U waves b. Peaked T waves c. Tall R waves d. Deep S waves
8. Severe hypercalacaemia is sometimes associated with:
a. Prolonged Q-T interval b. S-T segment elevation c. Peaked T waves d.
Widened QRS complex
9. Which electrolyte disturbance can cause Torsades de Pointes on the ECG?
a. Hypokalaemia b. Hypercalcaemia c. Hypomagnesaemia d.
Hyponatraemia
10. Hypomagnesaemia can cause:
a. Prominent U waves b. Peaked T waves c. Shortened Q-T interval d.
S-T segment depression
Case Studies
1. A 55-year-old gentleman presented to emergency with history of uneasy feeling
for last six hours. He gave history of suffering from hypertension, diabetes and
dyslipidaemia. He was taking Enalapril and Telmisartan for control of blood
pressure. He was on metformin and glimepiride for control of diabetes. His pulse
rate was 80bpm, regular and blood pressure was 130/90mmHg. His 12-lead
ECG is given in Fig.22.14. Identify the abnormality. What is the treatment?
III III aVR aVL aVF
V1 V2 V3 V4 V5 V6
25 mm/s. 10 mm = 1 mV
Fig. 22.14 Identify the ECG abnormality
Соседние файлы в папке Библиотека им академика М.И. Перельмана