Rapid intracardiac pacing for treatment of recurrent ventricular tachyarrhythmias in the absence of heart block

Antitachycardia pacing and low-energy cardioversion for ventricular tachycardia termination: a clinical perspective

When incorporated into tiered therapy implantable cardioverter defibrillators (ICDs), antitachycardia pacing (ATP) techniques have proved useful for termination of sustained monomorphic ventricular tachycardias (VT) and have the advantages of rapid delivery, absence of patient discomfort, and minimal battery drain. The efficacy of low-energy cardioversion (LEC) is similar to that of pacing techniques for VT termination, but LEC has the disadvantages of patient discomfort, atrial proarrhythmia, and greater battery drain compared with ATP. Acceleration of VT occurs with similar frequency with each technique. Neither technique should be used without back-up defibrillation capability in an ICD. VT termination algorithms are currently empiric and require repetitive arrhythmia induction and trials of ATP or LEC. Future studies of the risk and benefits of each technique are likely to define optimal programming strategies in tiered therapy ICDs.

Autodecremental pacing for the interruption of ventricular tachycardia and atrial flutter

The efficacy and safety of autodecremental pacing (ADP) to interrupt ventricular tachycardia (VT) and atrial flutter was examined. Once tachycardia was recognized, ADP was initiated using a short train of stimuli with gradual shortening (3%) of the interstimulus interval. ADP was applied to 13 consecutive patients during 75 episodes of VT (mostly following induction by ventricular stimulation). Successful interruption of VT occurred in 88% of the episodes. In 6 episodes (8%), ADP resulted in ventricular fibrillation and in 3 episodes VT was unaffected by ADP. The only significant discriminator between the failure or success of ADP was the rate of VT. ADP was also applied to 17 consecutive patients with an atrial flutter that was resistant to conventional antiarrhythmic agents. Successful conversion of atrial flutter to sinus was seen in only 8 patients (47%). A temporary acceleration to atrial fibrillation appeared in 3 patients (18%), and in 6 patients atrial flutter was unaffected by ADP. ADP was successful in 70% (7/10) of patients with type 1 (< 300 beats/min) atrial flutter. The authors conclude that ADP is beneficial in the interruption of VT and atrial flutter in a selected group of patients, especially with a slower rate of tachyarrhythmia (atrial rate during atrial flutter < 300 beats/min and ventricular tachycardia < 180 beats/min).

Electrical devices for treatment of arrhythmias

Electrical devices can be used for preventing and terminating tachycardia and for achieving hemodynamic improvement during a continuing tachycardia. Conventional approaches to tachycardia prevention include pacing at physiologic rates to prevent brady-cardia-related tachycardia or tachycardias associated with prolonged QT-interval syndromes. More exotic techniques, such as those involving stimulation during the refractory period, are undergoing investigation. Some tachycardias cannot be easily terminated or recur incessantly. Hemodynamics can be improved by pacing methods that result in a narrower QRS complex by coupled pacing and, in supraventricular tachycardias, by pacing rapidly enough to create atrioventricular block. Most clinical tachycardias are caused by reentry. Careful analysis of the timing of individual stimuli that successfully terminate tachycardias indicate that critical relations exist in the conduction velocity, refractoriness and physical properties and dimensions of the reentry circuit and the remaining myocardium. Elucidating these relations has permitted inferences into the mechanisms by which pacing terminates or accelerates tachycardias. A vast number of pacing patterns have evolved for use in tachycardia termination. None of these appear to be foolproof. There is widespread and justified concern about the risk of acceleration of tachycardia when antitachycardia pacing is used in the ventricle. Experience indicates that only a few patients are suitable for termination of ventricular tachycardia by pacing, but these carefully selected patients may do well. Both the results and the potential for widespread use may be better with pacing for termination of supraventricular tachycardia. Life-threatening tachycardias or fibrillation can be terminated by direct-current countershock. Although many technical problems remain, implantable cardioverter-defibrillators, possibly combined with antitachycardia pacemakers, will play an increasing role in the management or serious arrhythmias.

Ventricular tachycardia: historical perspective

Ventricular tachycardia is now diagnosed frequently in patients with organic heart disease. Although ventricular tachycardia was first demonstrated electrocardiographically 75 years ago, the natural history, fundamental mechanisms, and optimal management have remained elusive. Early observers commented on the rarity of occurrence and poor prognosis associated with this arrhythmia, yet with time, some patients with ventricular tachycardia were reported to survive for prolonged periods. Because of the sporadic nature of the arrhythmia and its variable prognosis, assessment of the efficacy of therapies has been difficult. A wide variety of treatments has been advocated with enthusiasm, but only a few have been consistently reported to be effective. Citation of historical data to claim benefit from new treatments should be viewed with caution.

Serial electrophysiologic testing with a permanent pacemaker after acute myocardial infarction

Electrophysiologic testing in patients after acute myocardial infarction may predict subsequent sudden death. We used a permanent pacemaker for repetitive electrophysiologic testing in a patient after acute infarction. Programmed, twice-threshold ventricular extrastimulation at two weeks after anteroseptal infarction failed to induce ventricular tachycardia. Subsequent programmed extrastimulation induced sustained ventricular tachycardia on four occasions (6, 16, 29 and 65 weeks) after infarction. As yet (20 months), spontaneous ventricular tachycardia has not occurred. Firm conclusions cannot be drawn from a single case. However, our patient developed a stable ventricular tachycardia circuit which was not apparent at two weeks. Thus, a single electrophysiologic study performed acutely after infarction may not accurately describe the potential for ventricular tachycardia or fibrillation. Serial electrophysiologic testing with an implantable externally triggered pacemaker may more accurately describe the potential for sudden death post-infarction in a few high-risk patients. This report shows that induction of ventricular tachycardia after acute infarction may not predict outcome.

Pacemakers in noncardiac surgery

The authors look at the use of pacemakers in three groups of patients: one with previously implanted cardiac pacemakers, one requiring temporary pacing systems for reasons related to their heart, and one in whom indications exist for permanent pacemaker implantation, but because of a surgical emergency, cannot have a permanent unit implanted before the noncardiac operation.

Risks of delayed potentials in pacemaker patients prone to ventricular tachycardia

Late potentials occurring after completion of the QRS complex have been observed in patients prone to ventricular tachycardia. They were recorded either during epicardial studies or in the catheterization laboratory. This paper describes such abnormal myocardial activity and discusses their potential effects on cardiac pacemakers.

Successful treatment by overdrive pacing of recurrent quinidine syncope due to ventricular tachycardia

A 54 year old patient who experienced recurrent ventricular tachycardia subsequent to quinidine administration for conversion of atrial fibrillation is described. Over a 10 hour period, 25 sustained episodes of ventricular tachycardia occurred for which electrical cardioversion was required in addition to numerous self-terminating paroxysms. Medical therapy with lidocaine, procainamide and propranolol was unsuccessful in controlling the arrhythmia. However, placement of a transvenous right ventricular pacemaker with overdrive pacing at a rate of 110 beats/min abrupty terminated all further ventricular ectopic activity during the period of quinidine elimination. Temporary overdrive pacing may be the treatment of choice for refractory, recurrent, ventricular tachycardia associated with quinidine therapy.

A multipurpose catheter for electrophysiologic and hemodynamic monitoring plus atrial pacing

A new multipurpose flow-directed pulmonary arterial catheter has been developed and evaluated in 30 patients with acute cardiopulmonary dysfunction. The catheter permits monitoring of the bipolar atrial electrogram, pulmonary arterial or wedge pressure, central venous pressure, and cardiac output, plus atrial pacing. The standard Swan-Ganz thermistor-equipped catheter was modified to incorporate two ring electrodes on the shaft at 25 and 26 cm from the tip. With the pair of electrodes positioned in the right atrium at the junction with the superior vena cava, stable electrograms of high quality were recorded in all 30 subjects, some for as long as six days. These high-fidelity atrial electrograms permitted rapid and accurate diagnosis of many complex dysrhythmias in these unstable patients. Because of the limited noise in the signal of the electrogram, continuous quantitative measurements of intervals by a computerized system was feasible. Furthermore, the stable intracavitary position of electrodes provided a reliable site for atrial pacing, with pacing thresholds (2 to 12 ma; average, 5 ma) that remained stable for up to four days. Atrial pacing was used to treat sinus bradycardia, atrial tachyarrhythmias, digitalis intoxication, and ventricular dysrhythmias.

Acute digitoxin intoxication treated by intracardiac pacemaker: experience in sixty-eight patients

Out of 124 patients who had taken massive doses of digitoxin in attempted suicide, emergency endocardial pacing was performed in the 68 with the worst prognosis. The mortality (13%) in the 124 patients compared favorably with the mortality (20%) in a previous series of 70 similar patients none of whom were paced. Sixteen (23%) of the 68 paced patients died. The causes of death were: asystole (two); cardiogenic shock (two); septicemia (one); and ventricular fibrillation (eleven). Ventricular fibrillation occurred during introduction of the pacing catheter in two patients, as a result of electrode displacement in these patients, because of premature withdrawal of the catheter in one patient, and for no detectable reason, during normally proceeding pacing, in five patients. Endocardial pacing has a place in the emergency treatment of massive digitoxin poisoning. Its chief hazards are mechanical, and one of the commonest is electrode displacement.

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.

The treatment of recurrent ventricular tachycardia with bilateral cervico-thoracic sympathetic-ganglionectomy. A report of two cases

Two patients had bilateral cervico-thoracic sympatho-ganglionectomy for treatment of disabling symptoms due to refractory ventricular tachycardia. In both patients treatment with antiarrhythmic drugs singly, in combination, or together with pacemaker overdrive had been ineffective in controlling this arrhythmia. Both patients had normal coronary arteriograms.

Bilateral thoracic sympathectomy appears to facilitate medical management of ventricular tachycardia in selected patients who are refractory to the usual medical treatment.

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.

Tachyarrhythmias in myocardial infarction

Tachyarrhythmias occur in about one third of patients with acute myocardial infarction (MI), and may precipitate serious consequences when they arise. Mechanisms of arrhythmogenesis in MI are imperfectly understood, but five categories of factors contributing to ectopic tachycardias are discussed. These include metabolic, anatomic, autonomic, hemodynamic, and iatrogenic causes. Each of the atrial, junctional, and ventricular tachyarrhythmias is briefly considered, and therapy is outlined.

Prevention of tachyarrhythmias and prompt treatment when they occur have substantially reduced mortality in acute MI, and constitute a primary objective of coronary care. However, better understanding of mechanisms of arrhythmogenesis, better systems of automated monitoring, and better modes of therapy, especially antiarrhythmic drugs, are urgently needed.

Acceleration of ventricular pacemakers by transient increases in heart rate in dogs during ouabain administration

The present experiments describe effects of transient increases in heart rate on ventricular pacemakers during digitalization. Fifteen anesthetized, vagotomized dogs were studied during ouabain infusion or after recovery from ouabain-induced ventricular tachycardia. Vagal stimulation was used to assess baseline ventricular automaticity and 30-second periods of atrial pacing were utilized to evaluate the response of ventricular pacemakers following different increments in rate. After an average dose of 45 ± 3 (SE) µg/kg of ouabain, vagal stimulation unmasked an automatic ventricular focus in 14 animals and pacing was followed by ventricular acceleration in all 15 animals. The Degrees of ventricular acceleration varied directly with the pacing rate. The increment in ventricular rate above the level unmasked by vagal stimulation averaged 59 ± 4% of the increment in atrial rate. At the higher driving rates, a transient postpacing depression was present before the emergence of a rapid ventricular focus. These findings were unaffected by beta-receptor blockade with 4-(2-hydroxy-3-isopropylamino propoxy) acetanilide (AY21,011). The results indicate that transient increases in heart rate may accelerate rather than depress ventricular pacemakers during digitalization.

Long-term pervenous atrial pacing

Long-term pervenous right atrial pacing has been used in five patients with intact atrioventricular (A-V) conduction for the treatment of refractory ventricular arrhythmias in two subjects and marked sinus bradycardia in three, two of whom also had paroxysmal supraventricular arrhythmias. The pervenous method was used to avoid a thoracotomy, and atrial pacing was chosen over ventricular pacing to preserve the normal A-V contraction sequence. Reliable atrial pacing was established in four cases, but one patient required ultimate conversion to a ventricular system because of irregular atrial capture. The most constant pacing was achieved by using a curved electrode with the tip positioned in the right atrial appendage.