Electrical Changes in the Heart – Roots far away from the Pump

Jomin Jose

M.Sc. Nurse, Medical and Surgical from Kerala University of Health Science, Thrissur

*Corresponding Author Email: jominjomon@gmail.com

ABSTRACT:

People usually possess a misunderstanding that ECG is getting changed with cardiac conditions only .But there are certain other conditions which have effect on the cardiac conduction that will be present on the electrocardiogram. The main conditions are glandular abnormalities, electrolyte disturbance and some neuronal problems. Hormonal problems are mainly due to excess or decreased production of thyroid and parathyroid hormones. The parathyroid hormone has an effect on the calcium level in the human body. Electrolyte difference creates clearly identifiable changes in the ECG. The main electrolytes in the body are calcium, potassium and magnesium. The rise or fall from the normal level in each of the electrolyte demonstrates its identical representation the electrocardiogram in response to each. The changes in waveforms in hypo and hyper calcaemia are same in hypo and hyper-parathyroidism. Vascular accident in the brain can cause arrhythmias in the heart rhythm which is more with the cerebral hemorrhage than with thrombosis .The neuromuscular disorders leads to cardiomyopathy and associated cardiac changes. .In case of hypo and hyper-magnesemia also the ECG depicts the same changes in the variations of potassium level in an individual. Hence the ECG alone cannot be a diagnostic tool in any of the following clinical conditions, along with the ECG blood test and other tests test should be used to finalize the diagnosis.

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INTRODUCTION:

Humankind cannot live in the universe without the vital organs in his body. Among the vital organs pivotal role is played by the heart .It act as a transporter or in another way a mechanical pump which help to transport the fuels for the cells that constitute the basic unit of animals.

It was only in the 18^th century more studies had been done in relation to the functioning of myocardium .In 1872; Alexander Murihead was the first physician who recorded the electrical activity of human’s heart. It took much more years to create a primitive form of present electrocardiography. It occurred in 1901 with the invention of Galvanometer by William Einthoven.

Later awarded as the father of ECG as well as won the Nobel Prize.(1)

In a normal heart the electrical impulse originate in the right top portion of the heart (Right atrium) in a place called Sinoatrial node (It is also called as the natural pacemaker of the heart).In simple way the power house in an electrical station. As same like the electrical energy supply from a hydroelectric station in the heart electrical impulse travel to entire heart through the conduction system .The main parts of this conduction system are AV nose, Bundle of his, Purkinje fibers.(2)

The PQRST waveform in a heartbeat is recorded with the help of four limb leads and six chest leads. In a normal individual the electrical activity is rhythmically repeating around 72 times in a minute. However, there are several situations which can alter the number of waves or the shapes of the electrical activity. Ninety percentage of this changes are in response to the abnormalities in cardiac itself. Nevertheless, multiple other factors can also affect the shape and the duration of the wave forms that may even have much importance in the confirmation of diverse clinical conditions.(2)

· Waves in response to the glandular abnormalities

a) Hyperthyroidism

The clinical condition in which the thyroid gland secrets excess amount of its hormone. These hormones have a direct control over the cardiac contraction rates. When the gland secrets more amount; cardiac pumping rates will also get increased.(3)

Clinical cardiac findings include:-

· Collapsing pulse

· Sinus tachycardia (Heart rate >100bpm)

· Wide pulse pressure

· Other atrial arrhythmias (atrial fibrillation is common)

· Cardiac enlargement

· Sometimes failure

Electrocardiogram changes:-

Usual changes

Ø Sinus tachycardia

Ø Atrial fibrillation with rapid ventricular response

Ø High voltage QRS complex

Rare changes

Ø Supra-ventricular arrhythmias(PSVT, Multifocal atrial tachycardia)

Ø Nonspecific ST and T wave changes

Ø Ventricular extra systole

b) Hypothyroidism

Clinical condition in which the individuals lack adequate amount of thyroid hormones in the body. Hypothyroidism results in the reduction of metabolic rates in the body. The number of hypothyroidism is much higher than hyperthyroidism since most of the time they are undetected.(3, 4)

Cardiac findings:-

· Bradycardia (Heart rate <60 bpm)

· Diastolic hypertension (DBP> 90 mm of hg)

· Narrow pulse pressure

· Cardiomegaly

· Pericardial effusion

Electrocardiogram changes:-

Usual changes

Ø Bradycardia

Ø Low QRS voltage in standard leads (<5mm).Generalized low voltage QRS in associated pericardial effusion.

Ø T wave appear flat or low voltage, however the ST segment remain without any deviation

Rare symptoms

Ø Prolonged QT interval

Ø Conduction disturbance, first degree AV block( PR > 0.22 sec)

Ø Interventricular conduction delay

c) Parathyroid hormones

The parathyroid gland secrets its hormone in the form of amino acids which helps to increase the ca²⁺⁺ level in the blood. Elevation in the hormone secretion leads to an increase in the body calcium level or vice versa.

The cardiological findings and the electrocardiographical changes are therefore similar to hypocalcemia and hypercalcemia. That will be discussed in the electrolyte disturbance part.(3)

· Waves in response to cation and anion changes in human

The electrocardiographic changes in a human body are mainly related to three electrons such as potassium, calcium and magnesium.

a) Potassium

Potassium is an important mineral take part in both intracellular and extracellular function. Movement of potassium in and out the intracellular and extracellular fluid result in cardiac contraction and relaxation. Normal level of potassium in a human body is 3.6-5.2 mmol/L.(1)

1) Hypokalemia

Less than the normal level is considered as hypokalemia, very low level such as less than 2mmol/L can be life threatening and require immediate medical attention.(5)

Cardiac findings:-

· Mild elevation in the blood pressure

· Abnormal heart rhythm

Electrocardiogram changes:-

Changes when potassium level falls below 2.7 mmol/L(7)

Ø Raise in the height and width of the P wave

Ø Prolonged PR interval or first degree AV block

Ø T wave flattening and inversion as the hypokalemia increases

Ø Appearance of U wave after the T wave.U wave become prominent as the T wave flattening and get inverted. Sometimes the U wave may join with the T wave to form TU complex (appearance of U wave in ECG is the classical sign of hypokalemia)

Ø ST segment depression in all the leads

Ø Long QT interval due to fusion of U and T waves

In case of sever hypokalemia (7)

Ø Frequent ventricular or supra-ventricular ectopics

Ø Atrial flutter, atrial fibrillation and supraventricular tachyarrhythmias

Ø Sometimes VT, VF, Torsades de pointes

b) Hyperkalemia

An increase in the potassium level greater than 5.2 mmol/L is called hyperkalemia. A significant increase in the level of 7mmol/L can cause severe hemodynamic and hematological consequence. Whereas an increase of 8.8mmol/L leads to sudden cardiac arrest or respiratory paralysis.(5)

Cardiac findings:-

· Slow, weak or irregular pulse

· Abnormal cardiac rhythms (arrhythmias)

· Sudden cardiac arrest

Electrocardiogram changes:-

Changes when potassium level above 5.5 mmol/L

Ø Tall T waves, especially in the precordial leads, clearly seen in V₂, V₃

Ø _Widenand flat P waves, at times P wave may be absent

Ø Increase PR interval

b) Magnesium

Magnesium is also an important intra-cellular cation in various body functions such as energy storage, utilization and transport, active role in all energy metabolism, regulation of normal cell membrane function and control of parathyroid hormone. Its importance is usually unnoticed in the clinical practice. Hence it is also called ‘forgotten cation’.

The normal range of magnesium in human body is 1.5-2.5 mmol/L. High or low levels leads to conditions called hyper or hypo magnesemia accordingly.(1)

1) Hypomagnesaemia

Hypomagnesaemia occur in mankind when the body level slip l below the ordinary level, i.e. < 1.5 mmol/L. Lower levels of magnesium can affect almost all functions in a human.(6)

Cardiac findings:-

· Cardiac arrhythmias

· Hypertension

· Tachycardia

Electrocardiographic findings:-

Ø Characteristic electrocardiogram is similar to hypokalemia

2) Hypermagnesemia

Identified by an unusual upstroke of magnesium level to >2.5 mmol/L.(6)

Cardiac findings:-

· Low blood pressure

· Abnormal heart rhythms, sometimes asystole

· Bradycardia

· > 5mmol/L – 1^st degree AV block

· >10mmol/L – 3^rddegree AV block

· >13mmol/L – asystole

Electrocardiogram changes:-

Ø This is similar to the waveform changes in hyperkalemia.

c) Calcium

Calcium ion in an individual plays important role in proper functioning and metabolism of a variety of cells and organs in the human body. It act as second messenger in the neuronal message transmission, helps in fertilization, cofactor in several chemical reactions in human body. Normal calcium level in human body is maintained as 4.5-5, 5mmol/L. It is also necessary for the growth and repair of bones.(2)

1) Hypocalcemia

It refers an unusual reduction in the body calcium level blow 4.5 mmol/L. It can affect all the functions in the cardiac system.(6)

Cardiac findings:-

· Hypotension

· Arrhythmias

· Increased heart beat

· Reduced contractility

· Congestive heart failure

Electrocardiographic changes:-

Ø Straight or long ST segment

Ø Prolongation of QT interval in an on and off manner in response to the prolongation of ST segment.

Ø Atrial and ventricular arrhythmias are common (torsades de pointes, ventricular tachycardia )

Ø Normal T wave

2) Hypercalcemia

It is a clinical disorder in which the calcium level in the body increased above 5.5 mmol/L.Excess amount of calcium in the body can leads to the bone become fragile, production of kidney stones, also affect cardiac and brain functions.(6)

Cardiac findings:-

· Reduced heart rate

· Increased contractility

Electrocardiographic findings:-

Ø Small ST segment sometimes cannot be visible

Ø Osborn wave (J waves- small notch at end of QRS )

Ø Short QT interval

Ø Atrial and ventricular arrhythmias

· Problems with the brain

a) Cerebrovascular accident

Majority of patients with cerebro-vascular accident have an ECG changes. These changes occur mainly in case of vessel break than the block in the brain.(7)

Electrocardiographic findings:-

Ø Sinus tachycardia

Ø Long QT interval with ischemic stroke

Ø Inverted tall T wave

Ø Sometimes tall wide T wave and prominent U wave

Ø Atrial arrhythmias

Ø Different blocks

· In impulse transmission disorders

a) Duchenne or pseudohypertrophic muscular dystrophy

It is a genetic disorder caused by mutation in the dystrophine gene located in the X chromosome.It manifested as skeletal muscle myopathy and cardiomyopathy. This hereditary disorder is transmitted to other generation through the female gender.(4, 7)

Cardiac findings:-

· Abnormalities in heart beat

· Dilated cardiomayopathy can occur and its associated signs and symptoms

· Congestive heart failure

Electrocardiographic findings:-

Ø Right ventricular hypertrophy

Ø Small PR interval <0.01 sec

Ø Presence of Q waves in limbic and lateral leads

Ø Arrhythmias (sinus tachycardia, supraventricular tachycardia, ventricular tachycardia )

Ø Bundle branch block, fascicular block

b) Friedreich’s ataxia

It is a rare hereditial disease that affect mainly the muscle and heart. Ninety percentage of patients with Friederich’s ataxia have a cardiac involvement usually hypertrophic or dilated cardiomyopathy. (6, 7)

Cardiac findings:-

· Arrhythmias

· Left ventricular hypertrophy in 75% of patients

· Conduction disturbance in 10%

Electrocardiographic findings:-

Ø Signs of left ventricular hypertrophy

Q wave in leads two and three, avf, V5, V6

Ø Features of dilated cardiomyopathy

Low voltage

ST depression and wave inversion

Bundle branch block

Ø Arrhythmias

Atrial flutter, atrial fibrillation, ventricular tachycardia

REFERENCES:

1. Chung NS. Practical electrocardiography. Peepee publications. 2000

2. Braunwald E. Heart disease, a text book of cardiovascular medicine. 5^th edition. Saunders publications.1997

3. Norman J. Hypothyroidism too little thyroid hormone. [Online].Available from. http://www.endocrineweb.com/conditions/thyroid/hypothyroidism-too-little-thyroid-hormone

4. Lederer E. Practical essentials. [Online].available from. http://emedicine.medscape.com/article/240903-overview

5. Lewis L J. Hyperkalemia.[online].Available from: http://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/electrolyte-disorders/hyperkalemia

6. Moe M S. Disorders involving calcium, phosphorous and magnesium. [online] Doi. 10.1016/j.pop.2008.01.007

7. Agarwal K.ECG abnormalities and stroke incidence. Expert review on cardiovascular therapy 2013:11(7)

*** picture courtesy http://image.google.coms

Received on 22.04.2015 Modified on 27.06.2015

Int. J. Nur. Edu. and Research 3(3):July-Sept., 2015; Page 263-268

DOI: 10.5958/2454-2660.2015.00005.8