Ventricular tachycardia And Its Clinical management
Introduction And Diagnosis
When three or more ventricular ectopic beats occur in succession, it is called ventricular tachycardia. The common causes are ischemic heart disease, myocarditis, digitalis toxicity, electrolyte disturbances and cardiomyopathies. Rarely it may occur in an otherwise normal heart. The ventricles beat regularly at the rate of 150-210/min. Slight irregularity may occur. The blood pressure is low and the patient may go into shock. The carotid message does not bring down the rate as in the case of supraventricular tachycardia.
Ventricular tachycardia is generally preceded by the occurrence of ventricular ectopics. Frequency of more than 6 ectopics/min., multifocal ectopics, ectopics occurring in succession and ectopics falling on the T-wave of the preceding beat (R on T phenomenon) are features which are associated with a high risk of developing VT.
Diagnosis: It is confirmed by the ECG which shows wide regular QRS complexes with evidence of dissociation between P-waves and QRS. Occasional sinus capture beats may be seen.
Ventricular tachycardia is a grave arrhythmia associated with high mortality, since it usually indicates serious underlying heart disease. Death is due to shock or transition to ventricular fibrillation.
Patients presenting with shock and ventricular tachycardia should be given DC shock of 100-150 joules to convert the rhythm to normal without delay. Antiarrhythmic drugs tend to aggravate hypotension. Pressor agents such as dopamine may be required if the blood pressure does not come up.
In uncomplicated cases, the drug of choice is lidocaine (Lignocaine). It is given as a 2% solution intravenously. Bolus doses of 50-100 mg are repeated (up to a total dose of 250 mg) till the tachycardia is arrested. The a maintenance dose of 2-4 mg/min is given continuously as an intravenous drip (1g added to 500 ml 5% glucose and 1-2ml given every minute). The drip is tapered off within 48-72 hours. If the VT recurs despite lignocaine, other antiarrhythmic drugs should be tried to control the arrhythmia. Drugs like procainamide, disopyramide, mexilitine, propranolol or amiodarone are given intravenously for immediate control of VT. Once the VT is controlled, oral maintenance therapy can be continued preferably with the same drugs. The following drugs are for oral use:
- Procainamide 1-3g daily in divided doses
- Quinidine sulphate 0.8-2g daily in divided doses
- Disopyramide 400-600 mg daily in divided doses
- Dilantin sodium 100mg thrice daily
- Propanolol 40-80 mg tid
- Mexilitine 200mg three or four times daily to start with and then to be tapered off.
- Amiodarone 200mg three times daily to start with and then to be continued at 100mg thrice daily.
In acute myocardial infarction with a slow ventricular rate, transvenous pacing to increase the heart rate prevents the development of ventricular tachycardia.
© 2014 Funom Theophilus Makama