​Differential diagnosis of antibiotics causing long QT interval on ECG are : 
-amantadine 
-erythromycin 
-ketoconazole 
-clarythromycin 
-ampicillin 
-pentamidine 
-sulfamethoxazole 
-trimethoprim 

​Differential diagnosis of anti arrhythmics causing long QT interval on ECG are : 
-sotalol
-amiodarone
-dysopyramide
-procainamide
-quinidine 

​Differential diagnosis of drugs / toxins causing long QT interval on the ECG are : 
-antihistaminics
-anti arrhythmics
-antibiotics
-thiazides
-serotonine antagonists
-novocamide
-cisapride
-quinine 
-tricyclic antidepressants 
-butyrophenone 
-phenothiazines
-chronic alcoholism 
-papavarin 
-insecticides

​Differential diagnosis of metabolic / endocrinological causes of long QT interval are : 
-hypothyroidism
-alkalosis
-extreme case of hyperkalemia 
-hypokalemia 
-hypocalcemia 

​Differential diagnosis of congenital causes of long QT interval on ECG are : 
-Ward – Romano Syndrome 
-Jervell and Lang Nielsen Syndrome 

​Differential diagnosis of long QT interval on the ECG are : 
-myocardial infarction 
-myocardial ischemia 
-congenital causes
-metabolic causes
-endocrinologic causes
-cardiomyopathy 
-sick sinus syndrome 
-mitral valve prolapse
-bundle branch block 
-complete heart block 
-myocarditis 
-toxins 
-drugs
-HIV infection 
-hypothermia 
-diabetic coma 
-dysproteinemia 
-chronic hepatopathy 
-hepatic coma
-cerebrovascular brain damage 
-glycogen storage disease
-amyloidosis 
-celiac sprue 
-nephrosis 
-hemochromatosis 

​Differential diagnosis of short QT interval on the ECG are: 
-hyperthyroidism 
-coronary heart disease
-digitalis medication 
-acidosis 
-hypermagnesemia 
-hypercalcemia 
-hyperkalemia
-sinus tachycardia

​Differential diagnosis of changing QRS complex on ECG are : 
-supraventricular extrasystoles
-premature ventricular contractions 
-intermittent bundle branch block 
-intermittent pre excitation complex

​Differential diagnosis of thin QRS complex on ECG are : 
-supraventricular extra systoles 
-sinus rhythm 
-polytope atrial ectopias
-atrial flutter
-absolute arrhythmia in atrial fibrillation 
-ectopic atrial rhythm 

​Differential diagnosis of supraventricular tachycardia in pre existing bundle branch block are : 
-atrial tachycardia 
-sinus tachycardia 
-atrioventricular re entry tachycardia