Sam B. Edwards

Isopotential body surface mapping in subjects of all ages: emphasis on low-level potentials with analysis of the method.

In this report we consider the body surface distribution of low-level potentials, particularly those of the U wave, the PR segment, and the ST segment in normal subjects. The long-term objective of this report is to study low-level body surface potentials, but adequate methods are required for that. Therefore, the primary emphasis in this report is artifacts that may occur in these potential distributions. Although receiving a secondary emphasis, the findings show that accurate low-level potential distributions can be recorded and they have interesting and distinctive features. The results present two features that are important in the construction of isopotential maps: 1) The normal distribution of the surface potentials characteristic of these signals, especially the U wave and the PR segment, and 2) the influence of subtracting or not subtracting these patterns in the process of constructing body surface maps for the entire cardiac cycle. An isopotential map method is described for identifying U waves. A reciprocal relationship was found between the normal body surface patterns of the U wave and the PR segment. If the period of the U wave was unfortunately chosen as the time for zero potential reference for all electrodes, the maps subsequently made for QRS and the ST segment were distorted on the anterior chest by an element of potential representing currents of terminal ventricular repolarization during overlapping T and U waves. The implication of these results is significant in that the timing of the reference baseline is critical in determining the pattern of the depicted map. These considerations are especially important in the interpretation of precordial and body surface maps recorded during exercise. The false patterns found can be quite misleading, since the baseline artifacts produce regional changes that may simulate patterns of abnormalities

The force-interval relationship of the left ventricle.

The force-interval relationship the dependence of cardiac contractility on the rate and pattern of stimulation has been shown to be independent of preload, but sensitive to the inotropic and disease state of the heart. The force-interval relationship was evaluated for the left ventricles of 42 patients, ages 1.5- 20 years, during cardiac catheterization using a micromanometer pressure transducer-tipped catheter and an atrial pacing electrode catheter. The left ventricular (LV) minor axis was monitored echocardiographically, and the end-diastolic dimension (EDD) and posterior wall thickness (PW) were measured. Hearts were paced at a variety of basic cycle intervals, to (1/heart rate), and two test stimuli were introduced at various times during a pause in the regular stimulation (test intervals t, and t2 were measured relative to the last regular systole before the pause). For t, < to and t2 2 tl + to Pma of the second test systole was greater than Pma for the last regular systole before the pause (equivalent to postextrasystolic potentiation). The ratio of these values of Pmax (test to regular) for systoles with equal LVEDDs, the force-interval ratio, was used to characterize the relationship. Patients were divided into three groups: group 1 (n = 17) patients had normal LVEDD, LVPW and pressure indices. Group 2 (n = 17) patients had increased LVEDD or LVPW but normal pressure indices. Group 3 (n = 4) patients had increased LVEDD and depressed pressure indices. The force-interval relationship was similar for groups I and 2: Pmax increased monotonically with t, or t2. However, the force-interval ratio was larger for group 2. The relationship for group 3 was different. Pmaz was a biphasic function of the test interval, increasing for small values of t, or t2 and decreasing for larger values of t,. The force-interval ratio was smaller than or equal to unity for short values of t,. This postextrasystolic depression was never found in groups I or 2.

Use of contrast echocardiography for evaluation of right ventricular hemodynamics in the presence of ventricular septal defects.

SUMMARY Intracardiac blood flow is altered in the presence of a ventricular septal defect (VSD), with different sizes of defects producing different flow patterns that can be visualized by peripheral injection contrast echocardiography. The utility of these patterns in allowing estimation of right ventricular pressure and resistance to ejection of blood from the right ventricle (RV) was investigated. Forty-four patients underwent 46 contrast echocardiographic procedures, all within 24 hours before cardiac catheterization. All patients were placed in one of four groups based on catheterization findings. Group I, which consisted of patients with no VSD, or a small VSD with a pulmonary-to-systemic flow ratio (Qp/Qs) < 1.5:1 and right ventricular pressure < one third systemic, had echo-dense material appear in the RV only. Group II consisted of those with moderate-sized VSDs with Qp/Qs 2 2.5:1 and right ventricular pressure 60-80% systemic; in these patients echodense material appeared in the RV and in the left ventricle (LV) anterior to the mitral valve. The contrast appeared in the LV in early diastole and cleared from the LV in systole, with none appearing in the aorta or left atrium. Time from the preceding QRS to appearance of echo-dense material in the LV divided by the R-R interval (appearance time to R-R interval ratio) was 0.62 - 0.69. Group III consisted of those with large VSDs, Qp/Qs > 3:1 and systemic right ventricular pressure with low pulmonary vascular resistance and no pulmonary stenosis. These patients had appearance of echo-dense material in the LV during early diastole anterior to the mitral valve as in group II, but the material remained in the LV to be ejected into the aorta. Appearance time to R-R interval ratio was the same as in group II. Group IV consisted of patients with tetrology of Fallot and one patient with a large VSD and increased pulmonary vascular resistance. Echo-dense material again appeared in the LV early in diastole and was ejected into the aorta during systole. The appearance time/R-R ratio was significantly less than in groups II or III, allowing a clear separation between those patients in group III from group IV. Contrast echocardiography allows estimation of the right ventricular pressure and evaluation of increased resistance to pulmonary flow due to either pulmonary stenosis (PS) or increased pulmonary vascular resistance in the presence of VSDs. This technique also provides a minimally invasive method which may be useful for serial evaluation of such patients, and will permit early detection of developing PS, and possibly increasing pulmonary vascular resistance. Decreasing right ventricular pressure due to spontaneous closure of the VSD may also be detected by this technique.

Heart block in children - Evaluation of subsidiary ventricular pacemaker recovery times and ECG tape recordings

SummaryTo evaluate subsidiary ventricular pacemaker function in 20 children with congenital or surgically induced complete heart block, we measured recovery times following overdrive ventricular pacing. Long-term ECG tape recordings were performed in eight of these children. Ages ranged fom 1 month to 17 years. The resting R-R intervals ranged from 595 to 1,740 msec. The ventricles were paced at various cycle lengths of 400 to 1,000 msec with either transvenous electrode catheters or surgically implanted epicardial electrodes. His bundle recordings showed that the site of block did not allow separation of patients with symptoms from those without symptoms. Prolonged recovery times were present in patients with block above the His bundle recording site who had symptoms of syncope or dizziness, as well as in patients who had a wide QRS. However, some asymptomatic patients with heart block above the His bundle recording site also had long recovery times. None of the asymptomatic patients who had ECG tape recordings had paroxysmal tachycardia in more than 300 hours of recordings. However, one symptomatic patient with congenital heart block and a prolonged recovery time had brief episodes of paroxysmal ventricular tachycardia that produced no symptoms at the time of recording. The results suggest that the coexistence of prolonged recovery times and paroxysmal tachycardia may be predisposing factors to the development of symptoms in patients with complete heart block. We believe that further electrophysiologic investigation of this possibility is warranted in patients with heart block.

Accessory atrioventricular pathway in an infant: prediction of location with body surface maps and ablation with cryosurgery.

A 10-month-old infant with multiple muscular ventricular septal defects, congestive heart failure, Wolff-Parkinson-White syndrome, and supraventricular tachycardia is presented. The site of ventricular pre-excitation was predicted by analysis of ST-T wave isopotential body surface maps to be in the posterior free wall of the right ventricle. The site was confirmed by epicardial mapping of the ventricles during surgery. The pathyway was cryoblated and the ventricular defects were closed. The patient has been free of pre-excitation and supraventricular tachycardia for over two years since surgery.

Sudden death after left stellectomy in the long QT syndrome

The long QT syndrome (LQTS), which is manifest by QT prolongation and episodic T-wave alternation accompanied by syncope and sudden death due to malignant ventricular arrhythmias after physical or emotional stress, has been well described. 1,2 If not treated, this syndrome carries a poor prognosis, with a mortality rate of as high as 78%. 1 Treatment with ~-blocking drugs is effective in most patients, and may reduce the mortality rate to 7%. 1 For patients refractory to ~-blockade therapy who remain at high risk for sudden death, left stellectomy, including removal of the upper thoracic sympathetic ganglia, has been recommended as the t reatment of choice 1,3 and has produced excellent results as judged by the absence of recurrent syncope. 3 We present a patient, however, who died suddenly 7 months after left stellectomy despite continued treatment with fl-blocking drugs.

Use of contrast echocakdiography for evaluation of right ventricular hemodynamics in the presence of ventricular septal defects

The use of a contrast agent is uniquely suited for describing intracardiac flow hemodynamics as it allows description of blood flow patterns within cardiac structures. While contrast echocardiography has been used to detect the presence of phenomena such as valvular insufficiency and right-to-left shunting across atrial or ventricular septal defects [1–3], it can further be used to evaluate abnormal pressure and flow states which may vary even in the presence of similar structural defects. As intracardiac pressure-flow relationships are altered by factors in addition to the size of the ventricular septal defect (VSD) itself, knowledge of the specific intracardiac flow pattern present can provide information permitting evaluation of the pulmonary vascular resistance and the presence or absence of pulmonic stenosis. In this chapter, contrast echocardiographic flow patterns present in varying hemodynamic states associated with a ventricular septal defect will be described to enable one to semiquantitatively assess right ventricular and pulmonary artery pressures. Such information coupled with estimation of total shunt size by techniques such as radionuclide angiography provides a very thorough evaluation of such a patient which in many instances would obviate the need for serial catheterizations.

8 Influence of Intracardiac Shunting on Left Ventricular Muscle Mechanics in Tetralogy of Fallot

The need continues for better quantitation of left ventricular function. Previous studies have indicated the nature of intracardiac shunting in tetralogy. Simultaneously recorded left ventricular pressure and biplane cines were analyzed to construct continuous left ventricular function curves in ‘normales’ and in tetralogy patients. The original measurements throughout 3–6 consecutive beats were analyzed by a digital computer with numerical and graphic outputs of: LV pressure, LV volume, rate of volume change (flow), LV mid-circumference and its instantaneous velocity, tension at the endocardial surface, work and power. The force-velocity-length and pressure-volume-flow relationships of the left ventricle were depicted in three dimensional plots during the active state (systole) of the LV muscle for normals and tetralogy patients. In normals, maximum flow and peak velocity of shortening occurred at high tension levels in mid-systole; whereas in tetralogy, peak flow and velocity occurred during ‘isovolumic’ contraction at lower tensions. The continuous ‘function curves’ were markedly abnormal in tetralogy with peak rate of flow and of circumference shortening occurring prior to opening of the aortic valve. The results indicate that the left ventricle in tetralogy functions more efficiently than normal and unloads 15 to 40 percent of its stroke volume during isovolumic contraction. This results in lower than normal stroke work values. (SPR)