The use of ventricular pacing for suppression of ectopic ventricular activity

Sustained Suppression of Premature Ventricular Contractions by a Three-Month Pacing Adjustment

Premature ventricular contractions (PVCs) that comprise more than 15% of total heartbeats can induce cardiomyopathy in patients with systolic dysfunction, and cardiac ablation is frequently used to reduce PVCs in this patient group. However, cardiac ablation is not entirely without hazards. We report a noninvasive method that dramatically reduced PVCs in a cardiac pacemaker patient from 31% to 3% in seven days by increasing the lower limit pacing rate from 50 beats per minute (bpm) to 60 bpm. Not only were our patient's PVCs reduced by the initial pacing elevation, but PVC levels were maintained below 5% even after the pacemaker's lower limit was returned to its original value of 50 bpm. This irreversible suppression of PVC activity following a three-month pacing elevation is a novel result that might be caused by ventricular remodeling of the original ectopic focus.

Spectrum of sinus node dysfunction in two siblings

Two siblings, ages 14 and 23, with various features of sinus node dysfunction have been reported. Sinus bradycardia was the presenting feature in both patients. During the follow-up period both patients developed various types of ectopic rhythms which increased with exercise. One of them developed "silent atrium" at the age of 23 and had cerebral embolus as a complication. The other patient had frequent syncopal episodes and had to be treated with a combination of electronic pacemaker and antiarrhythmic drugs.

Tachycardias and electrical pacing

Techniques of electrical pacing for the treatment of tachycardias are multiple. The choice of a suitable method for a particular tachycardia depends upon understanding the mechanism of the tachycardia and the pacing characteristics that will lead to interruption or suppression of the tachycardia, or to ventricular slowing. Electrical pacing is indicated for tachycardias when drug therapy alone has failed or cannot be initiated or continued, and only for those tachycardias that are likely to respond to this type of electrical stimulation. In either the circus movement type or the ectopic pacemaker type an ectopic tachycardia is more likely to be suppressed if the pacing site is near the site of origin of the tachycardia. Pacing more rapidly than the basic rate in order to prevent or abolish tachycardias is termed overdrive suppression. The mechanisms responsible for this phenomenon may be associated with release of acetylcholine, release of potassium, activation of an electrogenic sodium pump, increase in cardiac output and coronary flow, decrease in size of the heart with a consequent decrease in wall tension, and decrease in the inhomogeneity of recovery of excitability that occurs at more rapid rates in the non-ischemic heart. All of these effects of pacing suppress accelerated pacemaker activity or prevent emergence of conditions favorable for development of circus movement tachycardias. Paired, coupled, or rapid atrial pacing may improve ventricular performance or slow ventricular rate, or both, without abolishing the ectopic pacemaker activity. Atrial pacing with pacing sites located at endocardial, epicardial, coronary sinus, trans-septal, or esophageal locations may interrupt or prevent rapid supraventricular or ventricular arrhythmias. Similarly, ventricular pacing at endocardial, epicardial, myocardial, or transthoracic sites may be equally effective. Artificial pacing has abolished almost every type of tachycardia. Ventricular fibrillation always, and atrial fibrillation usually, require countershock if electrical treatment is to be employed, although defibrillation of the atria by rapid pacing has been reported once. Unipolar or bipolar pacemakers may be used temporarily, or permanently after implantation. Pacing rates used to abolish supraventricular tachycardias range from single premature beats to alternating current atrial pacing at 3600 cycles per minute. Artificial electrical stimulation of the heart may be on demand, or may be competitive (fixed rate). External magnets, induction coil coupling, and radio frequency signals allow competitive pacing to be used intermittently, with permanently implanted pacemakers. Thus, electrical pacing of the heart is a technique of major importance for the control of rapid heart rates.

Pharmacologic therapy of ventricular arrhythmias

To treat patients with ventricular arrhythmias properly, one must characterize the arrhythmia, define the underlying heart disease and look for and treat reversible causes. When arrhythmias are suitable for pharmacologic suppression, it is necessary to predefine therapeutic goals, then carefully document that the drug accomplishes these goals. Knowledge of a drug's metabolism, excretion, active metabolites and plasma protein binding is often required for full understanding of its clinical effect. Pharmacokinetic principles require that antiarrhythmic drugs be given on a rigid schedule and that plasma drug levels be frequently determined. Use of compartment models and the principle of superposition can enable one to achieve and maintain therapeutic drug concentrations while avoiding toxic side effects. The drugs commonly used to treat arrhythmias, lidocaine, propranolol, procainamide, diphenylhydantoin and quinidine, as well as some newer agents, have specific pharmacokinetics and toxic effects that must be understood.

Artificial pacemakers: indications and management

The development of artificial pacemakers for the electrical control of the cardiac rhythm has greatly enhanced the physician's ability to treat cardiac dysrhythmias. Pacemakers have been useful in treating Stokes-Adams syndrome and symptomatic bradyeardias; they have helped control the occurrence of tachyarrhythmias and have played an important role in the management of arrhythmias accompanying myocardial infarctions. With their more frequent use, pacemakers have contributed to our knowledge of underlying conduction and natural pacemaker disorders. As new indications for artificial pacemaking have been elucidated, more complex pulse generators have been developed, and newer technics found for their insertion. In spite of recent development the pulse generators in general use have a limited useful lifetime.

This paper reviews the indications for pacemaker insertion that are commonly employed. In addition, an approach to the problem of pulse generator replacement is presented.

Digitalis intoxication in patients with atrial fibrillation

The characteristic arrhythmias induced by digitalis glycosides in patients with atrial fibrillation are illustrated, and their mechanisms are described. The two effects of the drug which are most important in the genesis of such disturbances are: production of A-V nodal block and arousal of subsidiary pacemakers. These properties account for slow ventricular responses, escape beats, and nonparoxysmal junctional tachycardia. Less commonly observed arrhythmias include exit block from junctional pacemakers, and bidirectional tachycardia which may reflect blocking actions of digitalis in subnodal tissues. The recent development of His bundle electrocardiography and the immunoassay method of blood level determination permit more accurate appraisal of the clinical status of patients in whom digitoxicity is suspected. Treatment of junctional rhythms due to digitalis intoxication is usually passive. The occasional use of drugs, pacing, or cardioversion is discussed.

Glucagon in prevention and abolition of ouabain-induced ventricular tachycardia in normokalemic and hypokalemic dogs

A recent study suggested that glucagon has antiarrhythmic properties in addition to its positive inotropic effect. The present study was designed to evaluate the efficacy of glucagon in preventing and converting ouabain-induced ventricular tachycardia (VT) in normokalemic and hypokalemic dogs. Paired studies were made in ten normokalemic dogs and in eight dogs rendered hypokalemic by diet and hydrochlorothiazide. All dogs were pretreated with glucagon, and the amount of ouabain required to produce VT was measured. Each dog served as its own control in a second study in which normal saline was substituted for glucagon. When VT was produced during the control study, the response to a bolus injection of glucagon was evaluated. (1) Pretreatment with glucagon delayed the appearance of VT in hypokalemic dogs but not in normokalemic dogs. (2) Glucagon, by bolus injection, converted VT to sinus rhythm in 78% of the normokalemic dogs and in 100% of the hypokalemic dogs. (3) The mechanisms by which glucagon exerts its antiarrhythmic effect are not clearly defined.