Antegrade conduction and AV node function in patients with unidirectional retrograde accessory pathways

In 26 patients with unidirectional retrograde accessory pathways (URAP), antegrade conduction properties were evaluated. During electrophysiologic study the interval from the low septal right atrial potential to the His bundle potential (LSRA-H) in sinus rhythm (SR) was found to be less than 60 msec in 7 out of the 18 patients with left-sided URAP and in one out of two patients with septal URAP. Each of the six patients with right-sided URAP had an LSRA-H equal to or greater than 70 msec. During atrial extrastimulus testing, LSRA-H failed to prolong more than 100 msec (LSRA-H increment equal to or less than 100 msec) in four of six patients with left-sided URAP and LSRA-H of less than 60 msec in SR as well as in the one of two patients with septal URAP in whom the LSRA-H in SR was less than 60 msec. During rapid atrial pacing, we found 1:1 AV node conduction at a pacing rate of more than 200 bpm in the one patient with septal URAP and in 7 out of 14 patients with left-sided URAP who could be assessed. Three of these patients had progression from 1:1 AV conduction to 2:1 AV block without intervening Wenckebach. In conclusion, accelerated AV node conduction in SR and reduced AV node function during rapid atrial pacing or extrastimulus testing was found in 44% of our patients with left-sided or septal URAP. Since these patients are at higher risk for faster ventricular response to atrial flutter and fibrillation and for high frequency during supraventricular tachycardia, these findings were of clinical relevance.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Echocardiographic evaluation of left ventricular function in children with congestive cardiomyopathy

Echocardiography was used to study left ventricular function in 37 children with congestive cardiomyopathy. Left atrial and left ventricular diameters were approximately 1.5 times that predicted by body weight, whereas systolic decrease in left ventricular diameter (shortening fraction) and increase in posterior wall thickness were half that of normal children. The ratio of left ventricular preejection period to ejection time was increased in 25 patients and normal in 10. The mean velocity of circumferential fiber shortening was decreased in 30 of 34 patients and averaged 52 percent of that predicted by heart rate.

The shortening fraction was higher in the 12 patients who were asymptomatic at the time of study than in the 25 who had symptoms of congestive heart failure (19.6 ± 2.4 standard error of the mean versus 14.6 ± 1.2) (P < 0.05). In 11 patients whose condition improved after therapy with digoxin and diuretic drugs, serial echocardiograms showed significant increases in shortening fraction and posterior wall thickening and decreases in left atrial diameter and the ratio of preejection period to ejection time. However, one or more indexes of left ventricular function remained abnormal, despite the resolution of symptoms and a return of heart size to normal as judged from the chest roentgenogram.     

Response to isometric exercise in children and young adults with aortic regurgitation

We studied the hemodynamic response to isometric exercise in 28 children and young adults with aortic regurgitation (AR). Results were compared with those of 18 control subjects without heart disease. Sustained isometric exercise at 33% maximal handgrip capability produced similar increase in heart rate in the two groups. Systolic blood pressure rose to a greater extent in patients with AR than in controls (mean rise 33 mm Hg vs 13 mm Hg). Thirteen of 28 patients with AR had elevated left ventricular end-diastolic diameters at rest. During isometric exercise, left ventricular end-diastolic diameter remained constant in both groups. However, end-systolic diameter increased in patients with AR, resulting in a fall in shortening fraction. The mean left ventricular shortening traction of the patients with AR fell from 36.0 ± 1.0% to 32.8 ± 1.2% (p < 0.001), but did not change in controls. The fall in shortening fraction was most marked in patients with severe AR. We conclude that patients with AR have an abnormal cardiovascular response to isometric exerclse consisting of greater increase in blood pressure and a decrease in left ventricular fractional shortening.     

Prognosis for the newborn with transposition of the great arteries

To determine the prognosis for the newborn with transposition of the great arteries, the clinical course of 112 consecutive neonates with dextro-transposition was reviewed. Patients were managed with balloon atrial septostomy at initial cardiac catheterization, palliative operation if needed in the 1st year of life and Mustard's intraatrial baffle repair.The 1st month of life was the period of greatest risk (8 percent mortality rate). Between balloon septostomy and baffle repair, 14 of 103 patients at risk (14 percent) either died or had a cerebrovascular accident. The mortality rate at baffle repair was 14 percent (10 deaths in 71 patients), and there were 3 late postoperative deaths. Actuarial analysis of the data indicates that with this plan of management, approximately 50 percent of newborns with transposition of the great arteries will survive 5 years with excellent function and an additional 15 to 20 percent will survive with one or more medical handicaps.     

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. Electrophysiologic 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.     

Prolonged and decremental antograde conduction properties in right anterior accessory connections: Wide QRS antidromic tachycardia of left bundle branch block pattern without Wolff-Parkinson-White configuration in sinus rhythm

Four patients are described who had long conduction times and decremental conduction through right anterior accessory connections. None had Wolff-Parkinson-White syndrome on their ECG. Each had recurrent sustained wide QRS tachycardia due to antegrade conduction through the accessory connection. Three patients underwent epicardial mapping and successful surgical division of their accessory connection. Two of the three had a second accessory connection that was also divided surgically. Each of the three are free of tachycardial without medication. It is postulated that these accessory connections represent the remnants of anterior atrioventricular ring tissue described by Anderson.     

Mechanisms of cardiac arrhythmias after the Mustard operation for transposition of the great arteries

To determine the mechanisms of the cardiac arrhythmias frequently seen after the Mustard operation for transposition of the great arteries, intracardiac electrophysiologic studies were performed in 52 children 1 to 8 years after the Mustard operation. Sinus nodal automaticity as judged from the response to rapid atrial pacing was abnormal in 28 of the 52 children. Sinoatrial conduction (conduction of the sinus impulse to the atrium) was found to be abnormal in three of nine patients studied with the atrial extrastimulus method. Conduction of the sinus impulse from the high right atrium to the atrioventricular (A-V) node was abnormally delayed in only 2 of 41 subjects. The low lateral wall of the right atrium was depolarlzed late in 3 of 11 subjects (including the preceding 2). Two subjects showed delayed A-V nodal conduction and one delayed His-Purkinje conduction. The mechanism of supraventricular tachycardia induced in the laboratory was determined to be sinoatrial nodal reentry in four subjects and atrial muscle reentry in four. Two of the four with atrial muscle reentry had prolonged high right atrium to low lateral right atrium intervals during sinus rhythm.

Thus, damage to the sinus node remains the most common cause of arrhythmias after the Mustard operation. In addition, delayed atrial conduction may predispose to atrial muscle reentrant tachycardia.     

Electrophysiologic effect of digitalis on sinoatrial nodal function in children

Despite the prevalence of digitalis usage in children, the electrophysiologic effects of digitalis on sinoatrial (S-A) nodal function is unknown in this age group. The purpose of this study was to determine the effect of digitalis on sinoatrial conduction time as well as on S-A nodal automaticity. Ten subjects (mean age 10.5 years) underwent electrophysiologic assessment of S-A nodal function before and 30 minutes after administration of ouabain (0.01 mg/kg). Total S-A conduction time increased in each subject and the mean value after ouabain (182 msec ± 13 standard errors of the mean [SEM]) was significantly higher (P < 0.01) than before (149 msec ± 11). The sinus cycle length was variable after ouabain (P > 0.1). The corrected sinus nodal recovery time also was variable (P > 0.1), decreasing substantially in three subjects. Mechanisms of the effect of digitalis on the S-A node and atrium are proposed and discussed.

It is concluded that digitalis prolongs the S-A conduction time in children with normal S-A nodal function. By prolonging the S-A conduction time, digitalis may artifactually shorten corrected S-A nodal recovery time in some patients.     

Intracardiac electrography in children and young adults.

The interpretation of IE recorded in children has been hampered by a lack of agreement regarding normal values. We recorded IE in 158 children and young adults (ages, three days to 33 years) to define the various conduction intervals in normal and disease states. The HBP was recorded in 156 subjects. In 85 subjects with normal conduction indicated by surface ECG, including 19 subjects with normal hearts, there were no statistically significant age-related differences in internodal, A-V nodal, or His-Purkinje conduction intervals. Therapeutic levels of digitalis did not alter the conduction intervals. In 11 subjects with first degree A-V block and in five subjects with congenital complete A-V block, the site of block as determined by IE could not be predicted from the surface ECG. No abnormalities in conduction intervals were found in 18 subjects with right bundle branch block (surgically induced in 17 cases). Intracardiac electrography with recording of the HBP was found to be a safe, informative technique for electrophysiologic investigations in children and young adults.     

Prognosis of symptomatic coarctation of the aorta in infancy

Medical and surgical advances have improved the outlook for infants with symptomatic coarctation of the aorta. To help predict the clinical course of individual patients and to aid in individualizing their treatment, a 10-year experience with this condition was reviewed. Of 97 infants with symptomatic coarctation, 10 had isolated defects. In these patients, medical treatment was successful and surgical intervention could be postponed to allow for growth. The 87 other patients with associated cardiac defects were generally sicker at presentation and required earlier operation. Eleven of these died before surgical correction, 10 died at the time of repair, and 13 died later. The overall survival rate after 8 years was 62%, with most deaths occurring in the first 6 months of life. Late surgical results are flawed by a 32% rate of residual coarctation. Late postoperative hypertension is uncommon, and is usually attributable to a residual coarctation.     

Congenital diverticulum of the left ventricle

The clinical and hemodynamic features in a three-year-old boy with a congenital muscular diverticulum of the left ventricle associated with omphalocele, diaphragmatic hernia, and pyloric stenosis are presented. Preoperative angiocardiograms showed no obstruction to outflow from the diverticulum, the mechanism previously postulated as contributing to the spontaneous rupture and death reported in over half of the patients with this lesion. An intraventricular conduction delay noted on preoperative electrocardiograms disappeared after successful surgical removal of the diverticulum.