Mark D. Jacobstein

Concealed left atrial membrane: Pitfalls in the diagnosis of cor triatriatum and supravalve mitral ring

Cor triatriatum and supravalve mitral ring are forms of congenital left ventricular inflow obstruction produced by membranes within the left atrium. Typically, these defects occur as isolated anomalies with manifestations of pulmonary venous obstruction. Four children are presented whose left atrial membrane was associated with other significant cardiac defects, including, in one patient each, simple coarctation of the aorta, sinus venosus atrial septal defect, tricuspid atresia and complex coarctation of the aorta syndrome. The patient with the latter defect had undergone previous pulmonary arterial banding. None of these patients demonstrated significant pulmonary venous obstruction at cardiac catheterization. All patients had a normal value for either pulmonary arterial diastolic or pulmonary arterial wedge pressure. Three mechanisms explained the lack of pulmonary venous obstruction: (1) a large cross-sectional area of membrane openings, (2) an atrial septal defect that was confined to the pulmonary venous chamber and decompressed it by allowing blood to escape into the right atrium, and (3) decreased pulmonary blood flow. The diagnosis was facilitated by two dimensional echocardiography. Accurate diagnosis of left atrial membrane in the setting of other cardiac defects is of practical significance because pulmonary venous obstruction may occur after surgery for the associated defects.

Left ventricular systolic circular index: An echocardiographic measure of transseptal pressure ratio

An echocardiographic index of left ventricular (LV) short axis circularity can be defined by the equation: left ventricular systolic circularity index (LVSCI) = 4 pi(LV area) X 100/(LV perimeter). This index was measured from two-dimensional echocardiograms in 98 children (ages 1 day to 19 years) with congenital heart disease, and results were compared to right ventricular/left ventricular peak systolic pressure ratios (RVP/LVP) determined at cardiac catheterization. LVSCI was also computed in 50 children without cardiovascular or pulmonary disease to define the normal range. A short axis image of the left ventricle at the level of the papillary muscles was obtained from the left parasternal position. Area and perimeter were determined by computer planimetry of the LV endocardium at end systole. LVSCI was measured from three consecutive beats and averaged. In the normal group all values of LVSCI exceeded 93% (mean 96%). In the group with congenital heart disease RVP/LVP correlated exponentially with LVSCI: RVP/LVP = e2.6-0.04 LVSCI; with r = 0.88, SEE = 0.39, and p less than 0.001. If patients with suprasystemic right ventricular pressures (RVP/LVP greater than 1.2) are excluded, there is a linear correlation between RVP/LVP and LVSCI: RVP/LVP = 2.3-0.021 LVSCI; with r = 0.80, SEE = 0.14, and p less than 0.001. LVSCI could distinguish between patients with normal, mildly elevated, moderately elevated, and severely elevated RVP/LVP. We conclude that LVSCI is a readily determined parameter that is independent of age or body size and predicts RVP/LVP in children with congenital heart disease.

Magnetic resonance imaging in patients with hypoplastic right heart syndrome

Abstract ECG-gated magnetic resonance imaging (MRI) has been shown to provide excellent tomographic images of congenital heart defects. 1–4 Cardiac structures are especially well demonstrated because of the sharp distinction between relatively white myocardial walls or valves and the dark appearance of rapidly flowing blood within the heart. In particular, the clarity with which the endocardial and epicardial surfaces are resolved using MRI is superior to that produced by other noninvasive imaging modalities such as computed tomography (CT) or ultrasound and rivals the clarity produced by high quality cineangiograms. Thus, ventricular size, geometry, and wall thicknesses can be precisely defined. In this study, we examined the ability of MRI to depict the abnormal cardiac morphology in patients with known hypoplastic right heart syndrome (tricuspid atresia or pulmonic atresia with intact ventricular septum).

Myocardial protection during ischemia by prior feeding with the creatine analog: Cyclocreatine

The ability of 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine), a synthetic creatine analog, to protect myocardium during global ischemia was assessed in isovolumic rat hearts using phosphorus-31 nuclear magnetic resonance spectroscopy. Wistar rats were fed a 1% cyclocreatine diet. After 2 weeks, cyclocreatine-fed (n = 8) and control (n = 7) rats were anesthetized, the heart was excised and retrograde perfusion was begun at 10 ml/min per g with 37 degrees C, phosphate-free buffer containing glucose and oxygen. Hemodynamic and spectroscopic data were obtained during baseline, ischemia and recovery periods (each 24 min). During ischemia, the heart of control rats developed a rigor-like increase in tonic pressure (ischemic contracture) not seen in the heart of cyclocreatine-fed rats (22 versus 1 mm Hg, p less than 0.01). This change was associated with significantly more adenosine triphosphate (ATP) at end-ischemia in the cyclocreatine group (1.6 versus 0.6 mumol/g, p less than 0.01) and delayed development of acidosis (p less than 0.001). With reperfusion, the heart of cyclocreatine-fed rats spontaneously defibrillated sooner than did the heart in control rats (178 versus 346 s, p less than 0.03). Diastolic pressure remained significantly elevated throughout recovery in control hearts compared with treated hearts (p less than 0.001). Prior feeding with cyclocreatine preserves myocardial adenosine triphosphate during ischemia, delays the development of acidosis and ischemic contracture and improves recovery of mechanical function on reperfusion.

EVALUATION OF UNIVENTRICULAR ATRIOVENTRICULAR CONNECTION BY NMR IMAGING

Twelve patients (pts), ages 7 mos. to 23 yrs. (mean 11 yrs.), with known univentricular atrioventricular (AV) connection (“Single ventricle”) were evaluated by ECG-gated magnetic resonance imaging (MRI). Multiple sections were obtained in transverse, coronal and oblique planes using a 0.3T or LOT magnet and SE 30 pulsing techniques. MRI studies were evaluated using a segmental approach prior to reviewing the echocardiograms and angiograms which were available on all pts. MRI accurately depicted: 1) cardiovisceral and atrial situs 2) presence of splenic tissue 3) systemic and pulmonary venous connections 4) the mode of AV connection (i.e. absent right, double inlet, etc.) 5) the morphology and spatial relationships of the main and rudimentary ventricular chambers (6) the ventriculoarterial (VA) connections and 7) surgical procedures (i.e. shunts, PA bands). Seven pts had absent right AV connection, 4 had double inlet anatomy and 1 had an absent left AV connection. The absent AV connection was true atresia in 6 with invagination to the cardiac crux of fat-containing sulcus tissue which appears bright on MRI and an imperforate valve in 1. In 11 pts, the rudimentary chamber could be visualized. VA discordance was demonstrated in 2 pts with absent right AV connection, in all 5 with double inlet LVs and the 1 with absent left AV connection. We conclude that MRI accurately depicts cardiac morphology in pts with univentricular AV connection, often providing information not available with other imaging techniques.

ALTERATIONS OF ENERGY METABOLISM IN HYPERTROPHIED HEARTS DURING ANOXIA: A P-31 NUCLEAR MAGNETIC RESONANCE STUDY

The metabolic effect of anoxia on hypertrophied myocardium was investigated using P-31 NMR spectroscopy. Hearts from 18 mo. SHR (hypertrophied, n=7) and age-matched WKY (control, n=6) rats were mounted on a modified Langendorff apparatus, paced at 240/min and perfused with 36°C phosphate-free, glucose-containing buffer bubbled with oxygen or nitrogen (anoxia). Left ventricular pressure (LVP), LV dP/dt and perfusion pressure were continuously recorded while consecutive 3-min spectra were collected. This allowed temporal assessment of myocardial phosphate levels [incl. inorganic phosphate (Pi), creatine phosphate (CP) and ATP] during baseline conditions, anoxia and recovery. Anoxia was maintained until a 70% fall in LVP occured. Compared to the WKY, SHR rats had higher in vivo BP (163 vs 104; p<.001) and cardiac hypertrophy (heart/ body weight = 5.3 vs 3.5 mg/g; p<.001). During baseline perfusion, SHR hearts had higher resistance (9.8 vs 5.9 mmHg/cc/min/g; p=.003) but no significant difference in LVP or dP/dt. SHR hearts demonstrated a faster fall in high-energy phosphates and LVP during anoxia (SHR fell to 30% baseline LVP in 8.5 vs 13.0 mins; p=.018). Throughout the protocol SHR hearts had lower CP (3.8 vs 5.6 umoles/g; p=.008), ATP (3.2 vs 3.9 umoles/g; p=.047) and CP/Pi ratio (1.5 vs 2.5; p=.043). We conclude that chronically hypertrophied hearts have: (1) less ATP/g and CP/g than age-matched controls, and (2) a faster decline in mechanical and metabolic function during anoxia.

Comparison of ECG-Gated Magnetic Resonance Imaging and Two-Dimensional Echocardiography in the Evaluation of Patients with Congenital Heart Disease

Magnetic resonance imaging (MRI) has been shown to provide excellent tomographic images of congenital heart defects [1–5]. Cardiac structures are well delineated because of the sharp contrast between tissue walls and flowing blood. The technique is noninvasive, painless, and safe. Echocardiography is a widely accepted and powerful tool for evaluating patients with cardiac defects. The potential role of MRI, given the success and popularity of echocardiography, is uncertain. In this retrospective study, we compared MRI and ultrasound in the evaluation of patients with congenital heart disease.

EVALUATION OF AV CANAL DEFECTS USING ECG-GATED NMR IMAGING

Preoperative assessment of AV canal defects requires precise delineation of ventricular, septal and valvular morphology. In particular, recognition of ventricular hypoplasia is critical since it may preclude successful surgical correction. This evaluation is difficult even with cineangiography and 2-dimensional echocardiography. Nuclear magnetic resonance imaging (NMRI) is a new technique capable of providing excellent spatial and contrast resolution of cardiovascular structures without the need for contrast agents. We have used ECG-gated NMRI at 0.3T to evaluate 6 children with AV canal defects, including 3 with balanced chamber sizes, 2 with hypoplasia of the left ventricle and 1 hypoplastic right ventricle. All 6 defects were readily imaged and the 3 hypoplastic ventricles identified. AV valve morphology could be determined in 5 patients. Other frequently seen structures included papillary muscles, chordae tendinae and moderator bands. We conclude that gated NMRI is a valuable adjunct to angiography and echocardiography in the preoperative evaluation of children with AV canal defects.

EVALUATION OF PALLIATIVE SYSTEMIC-PULMONARY ARTERIAL SHUNTS USING NMR IMAGING

Palliative systemic-pulmonary artery (SP) shunts are frequently performed on children with cyanotic congenital heart defects which result in decreased pulmonary blood flow. Postoperative assessment of the adequacy of the shunt depends on physical examination, arterial blood gas analysis, chest x-ray and doppler-echocardiography. Direct visualization of the shunt, however, has required angiographic techniques at cardiac catheterization or, more recently, digital subtraction angiography. Nuclear magnetic resonance imaging (NMRI) is a new technique capable of providing high quality resolution of vascular structures without the use of contrast agents or exposure to ionizing radiation. We have used ECG-Gated NMRI at 0.3T to evaluate 6 patients with a total of 8 SP shunts including 4 Glenn shunts and 4 Blalock-Taussig (BT) shunts. 3 of 4 Glenn shunts and 3 of 4 BT shunts could be imaged. The size and course of the shunt could be seen in its entirety. 1 Glenn and 1 BT shunt, both patent, were not imaged. We conclude that NMRI is a safe, effective, non-invasive method for visualizing and evaluating patent palliative SP shunts. In our hands, NMRI has proved superior to echocardiography in visualizing these shunts.

214 VENTRICULAR INTERDEPENDENCE IN CYSTIC FIBROSIS (CF)

A two-dimensional echocardiographic study using short axis, long axis and four chamber views was performed to evaluate right ventricular (RV) and left ventricular (LV) geometry and interrelationships in 10 CF patients with severe obstructive lung disease and secondary cor pulmonale. All patients had clinical scores less than 50, vital capacity less than 55% of predicted, evidence of RV failure, hypoxia, and were receiving diuretics. Six patients were receiving digoxin. RV enddiastolic dimension (RVED), RV outflow tract (RVOT), ratio of RVOT to aortic root (AO) and ratio of RVED to LV end-diastolic dimension (LVED) were significantly (p< 0.005) larger than predicted normal values derived from M-mode studies. LVED was smaller than predicted. The massively enlarged RV encroached on the LV in all patients. This resulted in persistently abnormal interventricular septal configuration with bulging of the septum into the LV, an eccentric oval shaped LV chamber, and flat or paradoxic septal motion. This was associated with dyskinetic contraction and relaxation of the LV chamber, which could contribute to diminished performance. Thus massive RV enlargement may be a major factor in producing LV dysfunction in chronic cor pulmonale.