PAROXYSMAL TACHYCARDIA

Supraventricular Paroxysmal Tachycardia occurs frequently in people with no other discoverable abnormality. It is also seen in various pathological conditions—rheumatic heart disease, toxic goitre, etc., and in such an effort must be made to deal with the exciting cause.
Various measures may cut short a paroxysm. There are many methods, and patients soon learn which procedure is most effective. That which meets with success varies in individual cases, but remains fairly constant for any particular patient. Lying down flat, bending the head low between the knees when seated on a chair, holding the breath, attempting forced inspiration or expiration with nose held and mouth closed, pressure over the abdomen, and vomiting, are all procedures that patients may find useful in cutting short attacks. The physician may stimulate the vagus reflexly and strongly by pressure over the carotid sinus on one or other side, and this frequently arrests the paroxysm : the patient should lie on a couch, and pressure with the finger-tips of one hand should be exerted gently over a point level with the upper border of the thyroid cartilage at the anterior border of the sternomastoid. Meanwhile the heart should be auscultated, and abrupt slowing or cessation of the sounds is the signal for immediate release of pressure. If a first attempt is ineffective, success may follow repeated attempts or stimulation of the sinus on the other side. Cases resistant to sinus stimulation may yield to reflex vagal stimulation through the fifth nerve, from pressure on the eyeballs. Ocular pressure, however, is un¬pleasant and painful, and is now seldom employed. A tight abdominal binder is sometimes effective, especially in children.
In cases in which simple measures are ineffectual, attacks may sometimes be terminated by full digitalization, e.g. by the intravenous injection of 0-75 to i mg. of digoxin, the action being manifest in twenty to thirty minutes. It is essential before such intravenous therapy to be certain first that the patient is not already having digitalis treatment, and secondly that the rhythm is in fact supraven-tricular; digitalis is not a drug to use lightly in ventricular tachycardia. If this fails, quinidine sulphate by mouth in doses of 0-3 g. (5 gr.) three or four times a day may be effective. Hypodermic administration of 15 to 20 mg. morphine may secure needed rest for an anxious and exhausted patient. Supra-ventricular tachycardia is common in infants, in whom it may lead to severe congestive failure, and in whom digitalis in appropriate dosage is highly effective. Digitalis in anything like the adult dose is highly dangerous, and the average digitalizing dose for infants is 0-04 mg./lb. (0-09 mg./kg.) body-weight, given as the elixir in divided doses four or six-hourly.
With the development of pain or of symptoms and signs of congestive failure indicating exhaustion of the heart muscle, the need to arrest the paroxysm becomes more urgent. Should other measures have failed, treatment by intra¬venous quinidine or electrical cardioversion as practised for ventricular tachy¬cardia, may be required. The parasympathomimetic drugs (methacoline and carbachol) are now rarely used.
Attacks tend to cease spontaneously and are generally of short duration— minutes or hours. Every day that passes in a persistent case renders spontaneous arrest more likely, and whatever medicament is being used will probably be given the credit for the cure.
Ventricular Paroxysmal Tachycardia is less common than the other form, and generally occurs in older patients with grave myocardial disease, e.g. after recent coronary infarction. It may also occur from gross overdosage with digitalis. One rare form, however, is innocent and occurs in relation to exercise in apparently healthy people. In general, vagal stimulation and parasympatho¬mimetic drugs are useless in this form of tachycardia and treatment by quinidine, procaineamide or electrical cardioversion is required. Quinidine given orally in doses of 0-2 to 0-3 g. (3 to 5 gr.) two hourly is sometimes effective : the rate during the paroxysm may fall gradually under quinidine before normal rhythm is abruptly restored. Treatment in cases of ventricular tachycardia with grave cardiac disease and gross failure is more urgent than in the average case of supraventricular origin, and in these patients a quinidine sulphate drip given intravenously is of great value. Quinidine sulphate in a concentration of 3 g. (45 S1-) m 600 nu- °f saline is given by slow intravenous infusion at the rate of about 100 ml. per hour. It is essential that a close watch be kept upon the heart rate, and if possible electrocardiographic control or better, monitoring on an oscilloscope, is advisable. Gradual slowing of the high ventricular rate with sudden reversion to normal rhythm occurs in many cases after administration of from 0-3 to 1-5 g. (5 to 20 gr.) of the drug . Once normal rhythm has been restored, quinidine sulphate by mouth should be continued as described below.
Procaine has an action comparable to quinidine in ventricular ectopic rhythms, but its cerebral excitant action precludes its use m the unansesthetized patient. Its derivative, procaineamide, is devoid of this cerebral action, and can be used for treatment of extrasystolic arrhythmias. It is given orally in capsules ofo'25 g., or intravenously in 50 to 100 mg. doses repeated at intervals of a few minutes up to a total of i g. Reversion to normal rhythm, when it occurs, may be sudden. In some patients gross extrasystolic disturbances, even fatal ventricular fibrillation, may be provoked. Electrocardiographic control is most desirable. The blood pressure should be repeatedly estimated during the injection, since hypotension is a common side-effect. As with quinidine, this drug is unsuitable for use in general practice.
Prevention of Attacks.—Patients who have recently had attacks of paroxysmal tachycardia, or who are liable to repeated attacks, are generally benefited by maintenance doses of 0-2 to 0-3 g. (3 to 5 gr.) of quinidine sulphate several times daily over a period of weeks. Any exciting factor (excess of tobacco, caffeine or alcohol; thyrotoxicosis; septic foci in teeth or tonsils, etc.) should be attended to. Many patients are resistant and attacks recur at intervals over many years without serious effects on the health. In them continued quinidine therapy is unnecessary, but they should be given a supply of the drug for use during an attack. In cases of supraventricular paroxysmal tachycardia, reassurance as to
the innocent nature of the attacks is very important.
The smooth controlled action achieved by this method is clearly shown.
Cardwversion.—The technique of cardioversion, developed over the last few years, is becoming increasingly widely employed as the apparatus becomes available in this country. (The British Heart Foundation has gifted cardio-verters, each costing about ,£1,000, to teams in centres all over Britain.) In principle, the method employs a brief high-voltage (3,000 to 5,000 volt) Direct Current shock to depolarize the heart, so that on repolarization the sinus node with its highest rhythmicity reasserts its dominance. It is essential that the shock be timed to fall in the " safe period ", during early ventricular systole, since a shock at the end of systole (near the apex of the T-wave of the E.C.G.) may produce ventricular fibrillation, and shocks during atrial systole induce atrial fibrillation. Exact timing is secured by using the R-wave of the E.C.G. to trigger the shock, after a built-in predetermined delay of a few milliseconds-The voltage is built up in a condenser after stepping-up and rectification of ordinary mains A.C. supply, and the discharge is smoothed and prolonged bv an impedance in the circuit. A range of voltage is available, and calibration of the
energy used is in watt-seconds.
In use, the patient is connected to the built-in E.C.G., anesthetized briefly with intravenous thiopentone, and given one or more shocks at increasing voltage from large electrodes held against the chest so that the current traverses the heart. Preliminary use of quinidine, and suppressive doses after restoration of normal rhythm are advisable.
The results are impressive. Series running into three figures have been reported from various centres, from. which it is clear that the method is safe, and highly effective. Embolism is not a serious hazard. In atrial fibrillation over 80 per cent. of cases revert to sinus rhythm. Unfortunately, more than half of them relapse to fibrillation later. Repeated cardioversion in such individuals can, however, be undertaken.
Cardioversion can be used not only in atrial fibrillation, but in other disorders of atrial or ventricular rhythm—flutter, atrial and ventricular paroxysmal tachycardia, and ventricular fibrillation. For atrial fibrillation and flutter and for ventricular tachycardia it is probably safer than conventional drug therapy.
Beta-adrenergic Blockers.—Two types of sympathomimetic receptors are known, of which the beta group are concerned in cardiac ventricular excitability. Specific agents blocking these receptors have been devised: the first (prone-thalol) while effective was found to have carcinogenic effects .in rodents in long-term use, and has been withdrawn. Its successor, propranolol, is free from this drawback, and has been used for control of obstinate arrhythmias, and for treatment of angina. It has a specific additional use in the rare form of cardio-myopathy which mimics aortic valvular stenosis. Its value has not been finally established, but in oral doses of 10 to 20 mg. it is worthy of trial in cases of atrial fibrillation where digitalis fails to control an excessive ventricular rate, in recurrent paroxysmal tachycardia, and in gross extrasystolic arrhythmia. In angina it has been shown on occasion to increase exercise tolerance and reduce the frequency of attacks.