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The effects of verapamil, a slow channel blocker and a potent antiarrhythmic drug, on retrograde V-A conduction were investigated following diagnostic cardiac catheterization in 12 children premedicated with lytic cocktail. Surface EKG, intra-atrial and His bundle electrograms, as well as right ventricular pacing with use of extra stimulus technique were obtained before and after a single intravenous dose of verapamil (0.15 mg/Kg, max 5 mg). Verapamil prolonged the AH interval in 9/12 and abolished or prolonged the retrograde V-A conduction whenever present (abolition in 5/12 and prolongation in 1/12). The duration of retrograde V-A conduction exceeded the antegrade conduction time in all. It is concluded that verapamil abolishes retrograde V-A conduction whenever present and this phenomenon may further explain the antiarrhythmic effects of the drug on retrograde conduction dependent (reentrant) arrhythmias.

We previously reported that pulmonary artery pressures can be assessed in children with chronic rheumatic mitral valve disease by measuring right maximum spatial vector from Frank vectorcardiogram. To simplify the calculation, pulmonary artery systolic pressure was correlated with maximum negative deflection on Frank scalar X-lead (SX), maximum negative deflection on scalar Z lead (SZ), sum total of SX and SZ (SX+SZ) and combined SX and SZ. The patient material consisted of 30 children with chronic rheumatic mitral valve disease, aged 8-14 1/2 years. Eleven were male and 19 were female. Sixteen had mitral stenosis, 8 had mitral regurgitation, and 6 had combined mitral regurgitation and stenosis, documented by cardiac catheterization and angiocardiographic study. The results showed a significant correlation between pulmonary artery systolic pressure and SX (r=0.782). As calculation of SX is considerably easier and less time consuming than that of right maximum spatial vector, this simplified method is preferable to right maximum spatial vector for prediction of the pulmonary artery systolic pressure of children with pulmonary hypertension due to chronic rheumatic mitral valve disease.

Ouabain-induced tachyarrhythmias in cats can be abolished by bolus injection of NaHCO3 solution. This effect is consistent, rapid and of short duration. The antiarrhythmic effect appears to be due to high sodium concentration of this solution, as hypertonic NaCl solution with equal concentration of sodium exerts the same effect. Alkalinity and hyper-osmolality cannot account for the antiarrhythmic effect of NaHCO3 as respiratory alkalosis and mannitol solution with equal osmolality did not relieve the arrhythmias. Overdrive suppression is not responsible for this effect as the heart rate slows down during normalization of the cardiac rhythm. It is postulated that high Na+ concentration abolished ouabain-induced arrhythmias by competition with calcium ion in the myocardial cell sarcotubular system thus replacing it. This hypothesis is supported by the known effect of other agents such as sodium-EDTA and magnesium chloride, in digitalis-induced arrhythmias, which exert their antiarrhythmic properties by removal or displacement of calcium in the myocardial cells.

A comparative morphometric study was performed on the aortomitral valve apparatus of the embryonic and adult chicken hearts. It was found that the thickness of the aortic and mitral valve cusps diminishes dramatically as the embryo matures, however the relative length of the aortic valve, mitral valve and subaortic conus remains constant. A comparison of the aortomitral valve apparatus in chicken and man revealed that the subaortic conus is not completely resorbed in the fowl, whereas this process is well documented in the mammalian hearts. The implications of this observation on "the differential conal growth hypothesis" of transposition of the great arteries are discussed.

A heart specimen is presented which showed a rare combination of atrioventricular valve atresia with single ventricle, truncus arteriosus communis with an anteriorly placed trunk, ie transposition. Because of the problems involved in the classification of this heart, the types of single ventricle are revised with particular attention to the rare cases of atrioventricular valve atresia and single ventricle reported in the literature. Also the rare type of truncus arteriosus communis with truncoatrioventricular valve discontinuity is excluded from the so-called transposition complexes, and properly classified as a form of truncus. The literal meaning of transposition is stressed and it is urged to approach congenital heart defects in a purely anatomic sense with definition of each segment as accurately as possible. Thus the present confusion in terminology and further plethora of new terms are avoided.

A 10-month-old boy is presented who had isolated unilateral absence of the right pulmonary artery. He suffered from hemoptysis and severe congestive heart failure. The patient underwent prosthetic anastomosis of the right to the main pulmonary artery. Although the hemodynamic response was favorable, his oxygenation did not improve due to diffuse pulmonary arteriovenous fistulae of the affected lung. The patient succumbed 3 months after operation due to massive uncontrollable hemoptysis from the right lung. Isolated unilateral absence of the pulmonary artery is a rare lesion. In our review of the world literature as of November 1976, 47 cases (including this report) of the unilateral absence of the pulmonary artery have been reported. Of these 25.5% had pulmonary hypertension and only 4 cases underwent successful repair of the lesion. Though repair of this defect can be carried out, the result may not be always gratifying. Our experience with this case has led us to consider a lung biopsy before proceeding to the surgical repair of the lesion. If the affected lung shows arteriovenous abnormalities the operation should not be recommended.

Disopyramide has been successfully used to treat a variety of supraventricular and ventricular arrhythmias. The electrophysiologic effects of this drug were studied following diagnostic cardiac catheterization in 14 children aged 7 months to 14 years, suffering from congential heart disease. Surface EKG, intra-atrial, and His bundle electrogram as well as right atrial pacing with the use of extrastimulus technique were obtained before and after a single intravenous dose of disopyramide (2 mg/Kg, max 50 mg). The drug significantly prolonged the HV interval, effective and functional refractory periods of the atrium and the AV node. The most consistent change was the prolongation of the atrial refractory periods. The electrophysiologic effects of this drug on the conduction system have been variable and this variability has been attributed to the degree of vagal tone. The findings in this age group are similar to adults with simultaneous cholinergic blockade. This might be due to the direct depressant effects of disopyramide on the atrial and AV nodal tissue, and point to the potential usefulness of this drug in the pediatric age group.