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9. ECG Patterns Associated with Electrolyte Imbalances, Drug Toxicities and Physical and Chemical Agents
Intracellular concentration of K+ is approximately 30 times higher than the extracellular concentration in cardiac cells, while concentration of Na+ and Ca2+ is higher in extracellular fluid. Sodium and potassium pumps are active transport mechanisms responsible for resting membrane potential, depolarization, and repolarization of cardiac muscle cell. Hence appropriate concentrations of Na+, K+, and Ca2+ are important for normal depolarization and repolarization of cardiac cells. Any imbalance in the concentration of these electrolytes may lead to change in the pattern of electrocardiogram. Electrolyte imbalances are commonly seen in dehydration, severe vomiting, diarrheas, or renal failure. Electrocardiographic changes in response to electrolyte imbalances are detailed below.
9.1 ECG Changes Associated with Electrolyte Imbalance
Electrolyte imbalances | Alterations in electrocardiogram |
|---|---|
Hyperkalemia | – Large spiked “T” wave |
– Short Q-T interval | |
– Flat or absence of “P” wave | |
– Wide “QRS” | |
– Depression of S-T segment | |
– Prolonged P-R interval | |
– Sinoventricular rhythm | |
– Slowing of heart rate | |
– Decrease in R amplitude | |
– Complete heart block in severe hyperkalemia | |
Hypokalemia | – Progressive S-T segment depression |
– Small biphasic “T” wave | |
– Prolonged Q-T interval | |
– Appearance of U wave | |
– Tachyarrhythmia | |
– Delayed and abnormal repolarization | |
– Supraventricular and ventricular arrhythmias | |
– Increase in R amplitude | |
– Increased “P” wave amplitudes and durations (in severe hypokalemia) | |
Hypercalcemia | – Short Q-T interval. It may be fused with upstroke of “T” wave |
Hypocalcemia | – Prolonged Q-T interval |
– Tachyarrhythmia | |
– Q-T interval is correlated with plasma calcium levels | |
Hypermagnesemia | – Prolonged P-R interval |
– Widening of QRS complexes | |
– Heart block | |
Hypomagnesemia | – Decreased resting membrane potential of myocardial cells |
– Increased excitability of Purkinje fibers | |
– Wide QRS complexes | |
– S-T segment depression | |
– Peaked “T” wave | |
– Atrial fibrillation | |
– Supraventricular tachycardia | |
– Ventricular tachycardia | |
– Ventricular fibrillation |
9.2 ECG Changes Associated with Drug Toxicities
Drugs | ECG changes |
|---|---|
Amitriptyline | – Tachycardia |
– Arrhythmias | |
– Conduction disturbances | |
Acetylpromazine | – Sinus bradycardia |
Atropine | – Bradycardia followed by tachycardia is seen when atropine is given intravenously in doses higher than 0.015 mg/kg |
– Atrial premature complexes (APCs), ventricular premature complexes (VPCs), second-degree AV block, or sinus tachycardia may be seen when atropine is given in doses less than 0.015 mg/kg intravenously | |
Amitraz | – Bradycardia |
Amiodarone | – Arrhythmias |
– Conduction disturbances | |
– Bradycardia or a systole | |
Atenolol | – Bradycardia |
– Impaired atrioventricular conduction | |
Adrenaline | – Tachycardia |
– Arrhythmia | |
Aminophylline | – Tachycardia |
– Arrhythmia | |
Amphetamine | – Tachycardia |
– Arrhythmia | |
Aminoglycosides | – Tachycardia |
– Arrhythmias | |
Barbiturates | – Ventricular bigeminy |
– Ventricular arrhythmias | |
Bretylium | – Ventricular tachycardia |
Clindamycin and lincomycin (rapid IV in sensitive dogs) | – Cardiovascular collapse |
Clomipramine | – Cardiac arrhythmias |
– Tachycardia | |
Cimetidine | – Tachycardia (occasionally) |
Calcium gluconate (rapid IV infusion) | – Bradycardia |
– Shortening of Q-T interval | |
– S-T elevation | |
Cyclophosphamide | – Cardiac enlargement pattern |
– Low-output heart failure | |
Digoxin | – Prolongation of P-R interval |
– AV block (second or third degree) | |
– Sinus bradycardia or sinus arrest | |
– Ventricular premature complexes | |
– Accelerated junctional rhythm | |
– Ventricular tachycardia | |
– Paroxysmal atrial tachycardia with blocks | |
– Atrial fibrillation with slow ventricular rate | |
Doxorubicin | – Atrial premature complexes |
– Ventricular tachycardia | |
– AV block | |
– Supraventricular arrhythmias | |
– Heart block | |
Diltiazem | – Prolong AV node conduction time |
Diazepam | – Tachycardia |
– Normal QRS | |
Ephedrine | – Tachycardia |
Glycopyrrolate | – Increased heart rate |
– Ventricular premature complexes (less frequent) | |
Halothane | – Sinus bradycardia |
– Ventricular arrhythmias | |
Hydralazine | – Reflex tachycardia |
– Hypotension | |
Isoproterenol | – Ectopic complexes |
– Tachycardia | |
Isopropamide | – Tachycardia |
Imipramine | – Sinus tachycardia |
– AV bundle branch block | |
Lidocaine | – AV block |
– Sinus arrest | |
– Pace maker suppression | |
– Asystole | |
Morphine | – Bradycardia |
Nicotine | – Tachycardia |
Norepinephrine | – Sinus tachycardia or atrial tachycardia |
Neostigmine (ophthalmic) | – Bradycardia |
Neostigmine methylsulfate | – Cardiac arrest |
Organic phosphates | – Bradycardia or tachycardia |
Oxyphenonium | – Bradycardia followed by tachycardia and arrhythmias |
Prochlorperazine | – Tachycardia |
Propantheline bromide | – Tachycardia |
PGF2-alpha | – Tachycardia |
– Ventricular tachycardia | |
Prazosin | – Hypotension |
– Tachycardia (less frequent than with hydralazine) | |
Propranolol | – Pace maker suppression |
– Atrioventricular (AV) block | |
Physostigmine (ophthalamic) | – Bradycardia |
Quinidine | – Increased heart rate |
– Q-T prolongation | |
– AV blocks | |
– Ventricular tachyarrhythmia | |
– Sinus arrest | |
– Wide QRS | |
– Pace maker suppression | |
– Asystole | |
– Ventricular fibrillation | |
– Heart block (first, second, and third degree) | |
Salbutamol | – Tachycardia |
– Palpitation | |
Thiopental | – Cardiac arrest |
Terbutaline | – Direct stimulation of SA node may cause sinus tachycardia |
– Increased coronary circulation | |
– Enhanced myocardial perfusion | |
– Ventricular tachycardia | |
– Multifocal ventricular tachycardia | |
– Sinus tachycardia | |
– Atrioventricular (AV) block | |
Verapamil | – Pace maker suppression |
– Atrioventricular block | |
Xylazine | – Sinus bradycardia |
– Sinus arrest | |
– Sinoatrial block | |
– AV block | |
– Ventricular tachyarrhythmia |
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