John T. Flaherty

Influence of respiration on recording cardiac potentials. Isopotential surface-mapping and vectorcardiographic studies*

Abstract Isopotential surface-mapping studies in normal children indicated that inspiration produces an inferior shift of potential maxima and minima on the body surface with a concomitant decrease in their absolute potential values. There was a terminal maximum under the right clavicle with inspiration which was absent during expiration. Review of the body surface potential distribution provided a clearer picture of changing events of respiration than could be acquired from analysis of data acquired from a few selected points, as is done in vector-cardiography. Respiratory changes were more prominent in abnormal than in normal vector-cardiograms. It is suggested that when quantitative vectorcardiographic analysis is used for comparison of patient groups, it would be optimal to compare beats recorded during resting expiration.

Crossover from intravenous to transdermal nitroglycerin therapy in unstable angina pectoris

The present study was designed to examine the safety and efficacy of titrating a nitroglycerin infusion to a fixed hemodynamic endpoint as initial therapy for patients admitted to a coronary care unit for medically refractory unstable angina, and to test the hypothesis that patients, responding to the addition of intravenous (i.v.) nitroglycerin to their previous antianginal regimen, could be crossed over to nitroglycerin administered by a new transdermal delivery system. In 9 patients the nitroglycerin infusion titrated upward at 3- to 10-minute intervals until a 10% reduction in mean arterial pressure was achieved. This titration schedule and hemodynamic endpoint proved safe and effective for controlling episodes of chest pain at rest in all 9 patients. Subsequently, this treatment strategy was tested in 17 consecutive patients with unstable angina treated in our coronary care unit during a 1-month period. In 10 of 15 successfully treated patients ischemia was the cause of chest pain as documented by cardiac catheterization. No change was made in antianginal or vasoactive drugs during the period of i.v. nitroglycerin administration or during crossover to transdermal therapy. In this well defined subgroup of patients with unstable angina, nitroglycerin infusion decreased the mean arterial pressure from 101 +/- 18 to 87 +/- 11 mm Hg (mean +/- standard deviation), using an infusion rate of 84 +/- 74 micrograms/min (range 10 to 200). The mean duration of i.v. therapy was 36 +/- 12 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of Externally Recorded Radioisotope- Dilution Curves for Quantitation of Left to Right Shunts*

Abstract This study evaluated the use of radioisotope-dilution curves as a method for estimating the magnitude of left to right shunts. Following injection of radiohippuran into the proximal right pulmonary artery, curves were recorded during monitoring over the right lung. The curves were analyzed by comparing area ratios which were derived following extrapolation of the initial exponential disappearance slope. Statistical analysis indicated a good correlation between estimation of the magnitude of left to right shunts by the radioisotope as compared to the Fick method. Additionally, it was shown that (1) an improved correlation was obtained with the use of the quadratic regression equation as compared to linear regression; (2) an improved regression coefficient and decrease in the standard error of estimate was obtained by separating individual defects (ventricular defect, atrial defect and patent ductus) into separate groups as compared to the total group; and (3) estimation of the left to right shunt was obtained equally well in infants as compared to older children.

Cardiac Potentials on Body Surface of Infants with Anomalous Left Coronary Artery (Myocardial Infarction)

The body surface potential distribution in two infants with myocardial infarction secondary to anomalous origin of the left coronary from the pulmonary artery demonstrated: (1) the persistence of a minimum in the area overlying the infarct during inscription of the prominent Q wave in V6, and, (2) the presence of a terminal maximum in an adjacent area overlying the infarct. The terminal maximum was considered to represent peri-infarction “block” resulting from persistence of wave fronts in the ischemic muscle surrounding the infarct as suggested by the studies of Durrer and associates. Postoperatively, there was persistence of the initial minima overlying the area of the infarct. Finally, there was disappearance or marked diminution in the terminal maximum overlying the area of the infarct following surgical enhancement of myocardial blood supply.

Cardiac potentials in pulmonary disease. Overdistension of the lung versus cor pulmonale (right ventricular hypertrophy).

Abstract These studies demonstrated the distribution of cardiac potentials on the body surface in children with clinical evidence of overdistension of the lungs without right ventricular hypertrophy. The effect of the overdistended lung was shown to alter body surface events during ventricular activation by causing an inferior shift of potential maxima and minima during the middle third of the QRS. Roentgenographic studies demonstrated an associated inferior shift of the heart in relation to the anterior chest surface. Further shown was the associated diminished values of potentials over the left lateral chest during this interval in the patients with cystic fibrosis, as compared to normal children. The results of surface-mapping and x-ray studies indicated that leads placed in the fourth interspace monitor different body surface events during the middle of QRS in the cystic fibrosis children as compared to normal children due, in large part, to the inferior shift of potential maxima and minima. In the presence of cor pulmonale with marked right ventricular hypertrophy the potential distribution over the body was quite different in normal subjects and in those with cystic fibrosis. Right ventricular hypertrophy produced a migration of the anterior maximum in a rightward direction during the latter part of the QRS. Its terminal position was located beneath the right clavicle. These events differed from those in normal subjects and those with cystic fibrosis who showed a leftward migration of the maximum with a terminal distribution characterized by anterior minimum and posterior maximum.

The Role of Free Radicals in the Pathogenesis of Postischemic Reperfusion Injury

Spontaneous thrombosis of a coronary artery produces regional myocardial ischemia and ultimately an acute myocardial infarction. Recently, thrombolytic agents including streptokinase, urokinase, and tissue plasminogen activator (t-PA) have been used to dissolve the intracoronary thrombus within the early hours of an acute myocardial infarction. More recently percutaneous transluminal coronary angioplasty (PTCA) has also been utilized to reverse an acute coronary occlusion. Both of these procedures result in reperfusion of myocardium at risk for infarction. However, there is controversy as to whether reperfusion, while terminating ischemia, may actually cause a new form of damage to the region of myocardium at risk.