Peter P. Karpawich

Developmental sequelae of fixed-rate ventricular pacing in the immature canine heart: An electrophysiologic, hemodynamic, and histopathologic evaluation

Permanent, fixed-rate ventricular pacing (VVI) is associated with hemodynamic deterioration in the adult with compromised myocardial function. The effects of this pacing mode on the intact, immature heart, however, are largely unknown. Twelve beagle puppies (age 3 to 4 months) were equally divided into paced and age-matched control groups. All underwent identical hemodynamic and electrophysiologic evaluations. Transepicardial atrioventricular block and pacemaker insertion were additionally carried out in the paced group. After 4 months of observation, repeat hemodynamic and electrophysiologic measurements followed by histopathologic examinations were done in all puppies. The paced group exhibited significant (p less than 0.05) elevations of right atrial and pulmonary artery pressures, alterations in sinus node function, and prolongation of ventricular refractory periods compared with the control group. Initiation of dysrhythmias by programmed electrical stimulation was observed only among the paced group of puppies. Histologic examination demonstrated myofibrillar cellular disarray, dystrophic calcifications, prominent subendocardial Purkinje cells, and an increase in variable-sized, disorganized mitochondria only in the paced specimens. These findings indicate that permanent, apically-initiated VVI pacing ultimately predisposes to adverse cellular changes associated with hemodynamic and electrophysiologic deterioration in the intact, developing immature canine heart.

Congenital complete atrioventricular block: Clinical and electrophysiologic predictors of need for pacemaker insertion

Because of initial Adams-Stokes attack in the patient with congenital complete atrioventricular (A-V) block may sometimes prove fatal, there is a need to be able to identify the patient at great risk of having such attacks. Twenty-four children with congenital complete A-V block were followed up for 1 to 19 years to determine the efficacy of current methods of predicting risk for Adams-Stokes syncope and the usefulness of pacemaker therapy in relieving symptoms. The heart rate at rest, configuration of surface electrocardiographic complexes, data obtained during intracardiac electrophysiologic study and response to graded treadmill exercise testing were compared in children with and without syncope. One or more Adams-Stokes episodes were experienced by eight children, one of whom died. Only a persistent heart rate at rest of 50 beats/min or less demonstrated any significant (probability [p] less than 0.01) correlation with the incidence of syncope. Intracardiac electrophysiologic study was of little benefit because of site of block did not correlate with syncope. Although the increase in heart rate during treadmill exercise testing showed no correlation with prevalence of syncope or location of block, exercise-induced ventricular ectopic beats may have predictive value in older children and young adults. Ventricular pacemakers were implanted in 10 children. Each child was asymptomatic over a 1 to 10 year follow-up period. Because extreme bradycardia may contribute to the prevalence of Adams- Stokes attacks in children with congenital complete A-V block, careful evaluation of heart rate at rest may be an effective means of differentiating patients at risk of syncope. Pacemaker therapy is a feasible and effective method of treatment in young children and relieves symptoms

Successful surgical treatment of atrial, junctional, and ventricular tachycardia unassociated with accessory connections in infants and children

Five children with severe, life-threatening tachydysrhythmias were treated successfully with surgery. Three had atrial ectopic automatic tachycardia (AET), one had AV junctional (his bundle) automatic ectopic tachycardia (JET), and one had ventricular reentry tachycardia (VT). The mechanism and site of the tachycardia were diagnosed preoperatively using intracardiac electrophysiologic studies (EPS). Medical management with all available drugs failed to control the tachycardia in each patient. The two patients with left atrial AET underwent cryoablation of the focus using cardiopulmonary bypass. The patient with right atrial AET had removal of the anterior one third of the right atrial appendage and cryoablation of the edges. The patient with AV JET first had incision and suture ligation of the bundle of His and implantation of a ventricular pacemaker, but the tachycardia recurred 2 weeks later. Cryoablation of the bundle of His prevented further recurrences. Tachycardia stopped in the patient with VT during incision of a tumor in the apex of the left ventricle. No patient had tachycardia after surgery and none has required medical treatment.

Effects of verapamil on supraventricular tachycardia in children

Abstract Thirteen patients, aged 6 weeks to 16 years, with uncontrolled recurrent Supraventricular tachycardia were given intravenous verapamil in an attempt to abolish an episode of Supraventricular tachycardia. All patients had had intracardiac electrophysiologic studies to define the mechanism of their tachycardia. In seven patients conversion to sinus rhythm occurred after administration of verapamil: Five of the seven had atrioventricular (A-V) nodal reentry as the mechanism of their supraventricular tachycardia; the other two had reentrant tachycardia involving an accessory pathway. Verapamil was effective in abolishing the Supraventricular tachycardia in these patients, probably by prolonging the A-V nodal refractory period and conduction, thus breaking the reentrant circuit. In six patients there was no conversion to sinus rhythm: Four of the six had automatic atrial ectopic tachycardia and two had automatic junctional ectopic tachycardia. Among the four patients with automatic atrial ectopic tachycardia, a junctional escape rhythm developed in one, and second degree A-V block developed in the others. The two patients with junctional ectopic tachycardia had severe symptomatic arterial hypotension after verapamil and required resuscitation with intravenous calcium chloride. In spite of the good response to intravenous verapamil in the seven patients with reentrant tachycardia, only four of the seven could be maintained successfully on long-term oral therapy. The patients who experienced conversion to sinus rhythm with an intravenous bolus dose of verapamil but in whom Supraventricular tachycardia could still be induced with programmed stimulation could not be maintained successfully on oral therapy. It is concluded that verapamil is an effective antiarrhythmic agent that can (1) abolish the acute episode of Supraventricular tachycardia only in cases due to reentrant mechanisms, and (2) be used as an oral medication to prevent recurrences of supraventricular tachycardia in patients in whom the arrhythmia cannot be induced with programmed stimulation after intravenous doses of the drug.

Chronic epicardial his bundle recordings in awake nonsedated dogs: A new method

Recording cardiac electrical potentials from the region of the bundle of His in the awake, nonsedated animal would allow a more physiologic evaluation of impulse transmission through the specialized atrioventricular conduction system than anesthetized preparations. We present a new technique to localize and record chronic His bundle potentials using standard electronic equipment which obviates the need for intravascular catheters or an atriotomy. Six mature and four immature mongrel dogs underwent a midline thoracotomy. The bundle of His electrogram was recorded from the right atrial epicardium alongside the noncoronary aortic cusp. A flexible tripolar electrode probe with 3 mm interelectrode distance attached to a standard electronic recorder was used to localize the area of greatest His bundle impulse. Silver solder electrodes were sutured to the designated area and the wires were externalized to the back. Electrophysiological measurements were made 1 to 20 weeks later to confirm the accuracy and stability of the His bundle electrogram. These recordings were comparable to the standard internal catheter measurements both before and during atrioventricular impulse interference caused by atrial pacing or pharmacologic intervention. Electrodes sutured to the designated area do not interfere with impulse conduction and allow stable His bundle recordings in all activity ranges in the chronic animal.

Comparative electrophysiologic effects of digoxin in the nonsedated chronically instrumented puppy

The electrophysiologic effects of acute but not chronic administration of cardiac glycosides have been studied. Nineteen chronically instrumented beagle puppies underwent 2-week courses of parenteral digoxin in three dosage regimens: six received digoxin, 0.04 mg/kg/day; seven received 0.03 mg/kg/day; and 11 received 0.02 mg/kg/day. Mean serum concentrations were 3.2 ng/ml, 1.3 ng/ml, and 1.0 ng/ml, respectively. Significant electrophysiologic effects on sinus node function were produced only by the highest dose. Atrioventricular node conduction was significantly delayed among animals receiving both high and middle dosages. All three regimens significantly effected atrioventricular specialized conduction system functional refractory periods. Atropine decreased digoxin-induced effects on all measured parameters but totally eliminated the digoxin effect on the corrected sinus node recovery time.