TOF Patients Research Articles

Abstract 18727: Right Ventricular Pressure Overload is More Important than Volume Overload in Producing Contralateral Ventricular Dysfunction: A Congenital Heart Disease Model

Intro: It is known that right ventricular (RV) contractile failure predisposes the left ventricle (LV) to failure. Animal models in an acute setting indicate this phenomenon is due predominantly to RV volume overload causing both changes in LV geometry and suboptimal LV filling. We investigated the relative importance of chronic RV pressure versus volume overload in producing LV dysfunction using d-transposition of the great vessels with an atrial switch (TGA, RV pressure overload) and repaired tetralogy of Fallot with severe pulmonary valve insufficiency (ToF, RV volume overload) as model systems. Methods: We performed a single center retrospective analysis of cardiac magnetic resonance imaging (MRI) data. All adult patients with TGA and ToF who had useful MRI data were screened. Included ToF patients had pulmonary insufficiency without residual pulmonary or infundibular stenosis. Included TGA patients had mild or less aortic or tricuspid regurgitation. We assessed MRI derived LV and RV volume measurements. Correlations were assessed using Pearson’s correlation coefficient. Differences between correlation coefficients were assessed using a Fischer r to z transformation. Results: 32 TGA and 46 ToF patients met enrollment criteria with 35 and 72 MRIs respectively having data adequate for analysis. The groups were similar in terms of sex (58 versus 51% male) and age (29.6 +/- 6.0 versus 31.0 +/- 9.7) respectively. Patients with TGA demonstrated a strong correlation between RV and LV systolic function based on ejection fraction (EF) r=0.75. They also demonstrated a strong correlation between RV end-diastolic volume indexed to body surface area (EDVi) and LV EF (r=-0.56). Although there was a trend toward increased RV EDVi in patients with ToF (119ml/m2 versus 101ml/m2 for TGA p=0.11), ToF patients had a weaker correlation between RV and LV EF (r=0.46; p=0.02 compared to TGA) and a very weak correlation between RV EDVi and LV EF (r=-0.21). Conclusions: The present data indicate that in the chronic setting, RV pressure rather than volume overload is of greater importance in producing LV dysfunction, implicating shared muscle fibers, neurohumoral milieu, or relative unloading of the LV as playing a greater role in this process.

Differential effect of right ventricular dilatation on myocardial deformation in patients with atrial septal defects and patients after tetralogy of Fallot repair

Right ventricular (RV) volume overload results in RV dilatation in patients with atrial septal defect (ASD) and after tetralogy of Fallot (ToF) repair with pulmonary regurgitation. Study the differential effects of chronic RV volume loading on regional and global RV deformation in patients with ASD and after TOF repair. We studied 85 subjects: 50 patients after ToF repair, 15 patients with unrepaired ASD and 20 age-matched controls. The ToF patients and controls underwent an echocardiography at the time of a clinically indicated MRI. The ASD patients had a routine echocardiogram including RV volume calculations. Longitudinal deformation was analyzed using 2-D speckle tracking echocardiography. RV free wall global and segmental longitudinal deformation was significantly lower in ToF patients compared with ASD and controls (p<0.001). In ToF patients, there was a progressive decrease in strain values from base to apex (p<0.001), while in the ASD group there was a progressive increase (p=0.04). We found strong negative correlations between RV size and RV longitudinal strain measurements, strongest with RV length (R=0.72). When corrected for RV size, all ASD patients had normal or higher deformation values while half of the TOF patients had significantly lower values. Global and regional myocardial RV deformation is differently affected by chronic volume loading in ASD versus TOF patients, especially regarding the apical function. This suggests a different adaptation mechanism in both diseases. Our data also suggest that strain measurements are strongly influenced by ventricular size, which should be taken into consideration when interpreting strain values.

Medical Management Of Hypercyanotic Spells In Fallot’s Tetrology

Material and Methods: The study includes 45 patients with TOF who presented with cyanotic spells from amongst 142 TOF patients seen at the Congenital Heart Clinic at National Institute of Cardiovascular Diseases, Karachi, during one year period between October, 1980 to October, 1981. The diagnosis was made on clinical grounds, confirmed byEchocardiography and Cardiac Catheteriz ation and Angiocardiography. Results: Tetrology of Fallot was present in 142 of 814 new patients seen at the National Institute of Cardiovascul ar Diseases, Karachi between October, 1980 to Octob er, 1981. Forty -five patients, mean age 3.4±2.9 years (Range 0.3—10 years) presented with hypercyanotic spells. Nine patients were older than five years of age (Table 1). Discussion: The management alternatives of patients with Tetrology of Faflot depends upon the individual institution’s surgical expertise89. There are a few Centres in the World where surgical correction of infants with TOF can be safely undertaken under 1 year of age’°”. At our Institute complete repair of Tetro1og of Fallot can be taken at 3-4 years of age. For the smaller children we have performed Aorto-Pulmo-n ary shunt surgery. However, shunt surgery under 6 months of age carries significant mortality in our experience.

Modified short axis geometry for left ventricular assessment in patients with hemodynamically significant pulmonary regurgitation

Summary To determine the reliability of MRI LV measurements from a “modified” SA geometry compared with measurements from the standard SA geometry for repaired TOF patients with chronic pulmonary insufficiency. Background Standard MRI assessment of ventricular volume and mass is based on a stack of “standard” short axis images orthogonal to the LV horizontal long axis. Recently, we showed a modified short axis (SA) geometry more accurately defines the tricuspid valve plane, and thereby provides more reliable right ventricular volume estimates in normal subjects and repaired TOF patients. In order to use the modified SA stack as a replacement for the standard SA stack in routine studies, we wanted to prove its reliability for LV measurements. Methods The study was a comparison of cardiac MRI scans of 15 patients (10 male, age range 10 to 25 years) with TOF status post transannular patch repair. Subjects underwent cardiac MRI for standard clinical indications. In addition to standard SA cine SSFP stacks (Fig.1); a second stack of “modified” SA SSFP cines was obtained perpendicular to the RV outflow long axis (Fig.1). LV volumetry and mass were assessed by planimetry of the endocardial and epicardial LV borders at end-systole and end-diastole using MEDIS QMass software. LV volume and mass were measured for both sets of SA stacks (Figs.2-2) by 2 independent expert blinded observers at separate sittings. Agreement between the modified and standard geometry measures was determined by the intraclass correlation coefficients (ICC) and Bland-Altman analysis. Although there are no universal standards, values of ICC of 0.75 are considered high. Results There was excellent agreement for all left ventricular metrics between the standard and the modified SA geometries. The ICC for the two methods was 0.93 (p<0.001) for end-diastolic volume, 0.91 (p<0.001) for end-systolic volume, and 0.91(p<0.001) for LV mass. The Bland-Altman analysis showed no significant bias with limits of agreement <5% (Fig.1(5)). There was also excellent interobserver agreement for the modified short axis geometry with ICCs ranging from 0.91 to 0.95 for the three measures and Bland-Altman limits of agreement <7%. Conclusions The modified SA geometry showed excellent agreement of LV volume measurments compared with the standard SA geometry in this series of chronic RV volume overload patients. These results combined with our previous work showing improved RV assessment by the modified SA geometry makes this the preferred geometry for standard evaluation of repaired TOF patients.

Comparison of stroke work between repaired tetralogy of Fallot and normal right ventricular physiologies

Adult patients who underwent tetralogy of Fallot repair surgery (rTOF) confront life-threatening ailments due to right ventricular (RV) myocardial dysfunction. Pulmonary valve replacement (PVR) needs to be performed to restore the deteriorating RV function. Determination of correct timing to perform PVR in an rTOF patient remains subjective, due to the unavailability of quantifiable clinical diagnostic parameters. The objective of this study is to evaluate the possibility of using RV body surface area (BSA)-indexed stroke work (SW(I)) to quantify RV inefficiency in TOF patients. We hypothesized that RV SW(I) required to push blood to the lungs in rTOF patients is significantly higher than that of normal subjects. Seven patients with rTOF pathophysiology and eight controls with normal RV physiology were registered for this study. Right ventricular volume and pressure were measured using cardiac magnetic resonance imaging and catheterization, respectively. Statistical analysis was performed to quantify the difference in SW(I) between the RV of the rTOF and control groups. Right ventricular SW(I) in rTOF patients (0.176 ± 0.055 J/m(2)) was significantly higher by 93.4% (P = 0.0026) than that of controls (0.091 ± 0.030 J/m(2)). Further, rTOF patients were found to have significantly higher (P < 0.05) BSA normalized RV end-systolic volume, end-systolic pressure, and regurgitation fraction than control subjects. Ejection fraction and peak ejection rate of rTOF patients were significantly lower (P < 0.05) than those of controls. Patients with rTOF pathophysiology had significantly higher RV SW(I) compared with subjects with normal RV physiology. Therefore, RV SW(I) may be useful to quantify RV inefficiency in rTOF patients along with currently used clinical end points such as RV volume, pressure, regurgitation fraction, and ejection fraction.

Assessment of Coronary Flow Reserve in the Coronary Sinus by Cine 3T-Magnetic Resonance Imaging in Young Adults after Surgery for Tetralogy of Fallot

This study aimed to evaluate CFR by assessing blood flow in the coronary sinus and systemic endothelial function measured by FMD of the brachial artery in an open prospective study of 10 control subjects and 10 patients (ages, 15-25 years) who have undergone surgical TOF repair. Reduced ventricular function, impaired exercise capacity, and ventricular arrhythmia have been proposed as risk factors for sudden cardiac death after surgical repair of TOF. Some of this may be related to impaired myocardial perfusion. A 3.0T GE Signa Excite scanner was used to achieve phase-contrast, velocity-encoding cine magnetic resonance imaging in the coronary sinus before and during infusion with adenosine (0.14 mg/kg/min). FMD was measured in the brachial artery before arterial occlusion and 5 min afterward. The TOF group demonstrated significantly higher volumetric blood flow in the coronary sinus (282 ± 63 ml/min) than the normal control subjects at rest (184 ± 57 ml/min) (P = 0.006). During adenosine infusion, this difference disappeared. The CFR was 2.00 ± 0.43 in the control group and 1.19 ± 0.34 in the TOF group (P = 0.002). No correlation between FMD and CFR was observed in the study group (r (s) = 0.61, n = 8, P = 0.15). This study showed a reduced CFR due to a higher blood flow of the subject at rest in the TOF group. This reduced CFR may disable a normal adaptation to increased oxygen demand during exercise and increase myocardial vulnerability to reduced blood supply postoperatively for TOF patients with coronary heart disease.

Electrophysiology Issues In Adult Congenital Heart Disease

Improved surgical outcomes in children have led to a growing population of adults with congenital heart disease. Rhythm disturbances in the adult congenital heart disease (ACHD) patient can be intrinsic to the anomaly or acquired after palliation. Tachyarrhythmias, either supraventricular or ventricular, and bradyarrhythmias, either sinus node dysfunction or atrioventricular block, may occur frequently. Technological advances in intervention and surgical approaches have led to prophylactic and therapeutic reduction in arrhythmias. In order of escalation, this article addresses medical management, catheter ablation, device therapy for antitachycardia pacing and defibrillation, and surgical intervention. There are now an estimated one million-plus ACHD patients living in the United States. An estimated 45% of those have simple defects (e.g., atrial septal defects), 40% have moderately complex defects (e.g., tetralogy of Fallot, or ToF), and 15% have severely complex defects (e.g., single ventricle anatomy or surgical palliations for transposition of the great arteries [TGA]). The moderate and severe categories have a high incidence of arrhythmia. Of older repaired ToF patients, 34% develop symptomatic atrial or supraventricular tachycardias, 8.5% develop high-grade ventricular tachycardia (VT), and there are an increasing number of implantable defibrillators due to a sudden-death estimate of 2% per decade. Thus, an estimated 50,000 adults with repaired ToF will require electrophysiology follow-up with 100 sudden deaths per year nationally. Roughly 3% of all congenital heart surgeries requiring cardiopulmonary bypass have post-operative AV block, and 1% will require permanent pacing. Older atriopulmonary Fontans have up to an estimated 50% incidence of atrial tachycardia within a decade of palliation due to suture lines and elevated atrial pressures. Patients who have undergone an atrial switch operation (e.g., Mustard or Senning operations) are rarely exclusively in sinus rhythm a decade after repair, thus posing problems for rhythm control and anticoagulation. Catheter ablation in congenital heart disease is often more challenging than structurally normal hearts because of abnormal anatomy (congenital and/or post-surgical) and thicker chamber walls due to unfavorable hemodynamics. In preparation, review of noninvasive imaging, previous catheterization angiography, and surgical palliation reports are paramount prior to a procedure. Fortunately, to meet the growing challenge, newer software with 3-D packages allow for improved mapping. In addition, advances with larger-tipped and irrigated-tip catheters allow for deeper, more effective lesions to be placed. Several advances in surgical approach have led to a reduction in arrhythmias. For example, the arterial switch operation for d-transposition of the great arteries instead of the aforementioned atrial switch operation eliminates the use of a systemic right ventricle that can later develop intra-atrial reentrant tachycardia and sinus node dysfunction. Other advances include paying careful attention to minimizing ventriculotomies in ToF and ventricular septal defect (VSD) repairs, earlier complete repairs, and valve sparing to reduce pulmonary insufficiency. Finally, completion of the extra-cardiac Fontan procedure (e.g., total cavopulmonary connection) for single ventricles avoids extensive suture lines in the right atrium, thereby reducing scarring and higher pressures that lead to IART and sinus node dysfunction. Extracardiac (EC) conduits and lateral tunnel (LT) Fontans are preferred today, and the Fontan conversion procedure (converting prior atriopulmonary Fontans to the EC or LT type) can be performed to reduce arrhythmia and thromboembolic events.

Correlation of pulmonary regurgitation fraction and right ventricular ejection fraction in patients with tetralogy of Fallot

Sirs:We would like to comment on the Letter to the Editor byDalla Pozza et al. [1].TOF patients show a broad spectrum of right ventricular(RV) volume overload mainly due to pulmonary regurgi-tation (PR) during the postoperative course. Dalla Pozzaet al. [1] stated that TOF patients with significantly ele-vated indexed RV end-diastolic volume (RVEVDi), e.g.with an RVEDVi[150 ml/m

Right ventricular strain in patients with tetralogy of Fallot

Background Left ventricular (LV) circumferential strain shows cardiac dysfunction earlier than ejection fraction. However, measuring right ventricle strain is technically challenging due to the thin RV wall and complex morphology. Also, the predominant RV strain is longitudinal, whereas the predominant LV strain is circumferential. We recently validated a feature tracking algorithm for evaluation of left ventricular strain. Based on that work, we hypothesized that feature tracking would provide accurate and reproducible RV strain metrics for use in longitudinal evaluation of repaired TOF patients. Methods Forty patients and sixteen normal controls were evaluated. All patients had pulmonary regurgitant fraction > 30% with no residual obstruction. We dichotomized the TOF patients by RVEF ( 55%) for analysis. CMR image analysis included routine volumetry. Circumferential LV and longitudinal RV strain were calculated using the previously validated feature tracking algorithm. The average strain at the mid-ventricular level was used for comparison. Means were compared using student’s t-test and variances were compared with the Lev1:med test. Results All images yielded interpretable LV circumferential and RV longitudinal strain curves. All control subjects had normal biventricular ejection fraction. They had mean longitudinal right ventricular strain = -21+/-5%. The mean RV strain of patients with TOF and normal EV was -19 +/- 12%, not statistically different than normal. However, the variance in the strain as group was 2.5x higher than controls (p 55%) have markedly variable strain with increased dispersion in regional strain values. TOF patients with

Internal flow fraction as a potential indicator of pulmonary valve replacement in tetralogy of Fallot patients

Background Standard of care for TOF patients is a complete surgical repair in infancy but this results in free pulmonary regurgitation as no suitable long-term substitute for the obstructive valve is available. Although chronic pulmonary regurgitation can be well tolerated for decades, many patients (>20%) eventually develop right ventricular dysfunction and often require PVR. Determining the optimal timing of PVR is difficult, and there is no clear consensus within the medical community. In TOF patients before PVR, clinical studies have demonstrated a correlation between QRS duration and RV size with negative electromechanical interaction and dyssynchrony that progresses with RV enlargement. IFF is a quantitative measure of the energy loss throughout the cardiac cycle due to dyssynchronous contraction. We have developed a means of quantifying IFF noninvasively from cardiac magnetic resonance (CMR) images. In this study, we hypothesized that IFF within the left ventricle would increase in serial CMR exams prior to PVR.

Precise automated determination of the total and segmented right ventricular volumes for functional studies of the right ventricle using CMR

Background Cardiac magnetic resonance (CMR) is an acknowledged standard for quantification of left ventricular volumes, but the acceptance of CMR to measure the volume of the right ventricle (RV), including sub-units, such as inlet, outlet, and apical segment has been limited. In patients with Fallot (TOF), the size and function of the right ventricular outflow tract (RVOT) in the course of an RR-interval can serve as indication for re-operation in cases of pulmonary stenosis, regurgitation, or RVOT aneurysms. in addition to the results of conductance examinations. However, none of the available software applications provides a suitable systematic subdivison of the total volume. A novel algorithm was developed for this purpose and tested in this study. Methods We present an automated method for the determination of RV volumes based on short axis cine series from CMR examinations. The contour detection proceeds iteratively through slices and phases. Manual interaction is possible. For further functional analysis of the right ventricle, a subdivision into compartiments is applied. The subdivision is performed automatically from flat or curved layers as defined by landmarks identified by the investigator. The landmarks include the crista supraventricularis, the set in of trabeculary structures, and the apex. The conventional definitions of the compartiments are loose, therefore two definitions of the outlet are compared to each other: one robust and simple definition using flat separating layers, and a more complicated but flexible definition based on a curved layer. Results Depending on the quality of the images, this contour detection is successful (i. e. requires no further manual interaction) in up to about 95% of images in the midventricular region. Papillary structures in the apex as well as a weakly separable atrium in the basal region may require manual interactions. Volumes are provided for all phases in total and in specific regions. Stroke volume and ejection fraction arise naturally. The volumes obtained from the two outlet definitions turn out to agree typically within 10% of the total volume and thus do not lead to contradicting conclusions. Conclusion The application of this fast iterative contour detection method and volumetry may allow the evaluation of the chamber volumes for the full heart cycle in clinical routine. The automatic volume segmentation provides useful information about the function of a particular segment such as the RV outlet in TOF patients where it can complete the indications for a surgery.

Serial follow-up of biventricular function, exercise capacity and NT-proBNP measurements in repaired tetralogy of Fallot: is there a role for MR stress imaging?

163 ± 25 ml/m 2 to 183 ± 29 ml/m 2 ); these parameters did not change in subgroup I. Biventricular function remained stable during follow-up in all subgroups. Biventricular contractile reserve was preserved in all patients. VO2 max. decreased during follow-up, particularly in subgroup II, but this was not statistically significant. After PVR, RV volumes and PR decreased significantly; RVEF and LV contractile reserve increased. A lower RV contractile reserve at baseline correlated with a larger RVEDV at follow-up and with an interstudy decrease in VO2 max. NT-proBNP levels were significantly higher than in healthy controls (at follow-up 13 ± 10 pmol/l (patients) vs. 4 ± 2 pmol/l (controls)) but did not change over time and were not different between the subgroups. Conclusion RV volumes and PR percentage increased significantly over time, but only in TOF patients who had a RVEDV ≥ 150 ml/m 2 at baseline. Exercise capacity tended to decrease at 5-year follow-up, but biventricular function, biventricular contractile reserve, and NT-proBNP remained stable, irrespective of baseline MRI measurements. Baseline RV MR stress measurements correlated with important follow-up measurements of RV size and exercise capacity. Stress MRI showed clinically relevant changes after PVR. Stress imaging might be of additional value in the follow-up of TOF patients. In our patients, NT-proBNP provided limited additional information during follow-up.

Hypoxia induces PGC-1α expression and mitochondrial biogenesis in the myocardium of TOF patients

PGC-1alpha, a potent transcriptional coactivator, is the major regulator of mitochondrial biogenesis and activity in the cardiac muscle. The dysregulation of PGC-1alpha and its target genes has been reported to be associated with congenital and acquired heart diseases. By examining myocardium samples from patients with Tetralogy of Fallot, we show here that PGC-1alpha expression levels are markedly increased in patients compared with healthy controls and positively correlated with the severity of cyanosis. Furthermore, hypoxia significantly induced the expression of PGC-1alpha and mitochondrial biogenesis in cultured cardiac myocytes. Mechanistic studies suggest that hypoxia-induced PGC-1alpha expression is regulated through the AMPK signaling pathway. Together, our data indicate that hypoxia can stimulate the expression of PGC-1alpha and mitochondrial biogenesis in the cardiac myocytes, and this process might provide a potential adaptive mechanism for cardiac myocytes to increase ATP output and minimize hypoxic damage to the heart.

Arrhythmias Late After Repair of Tetralogy of Fallot-A Japanese Multicenter Study-

Arrhythmia is a major late complication in adults with repaired tetralogy of Fallot, although a large-scale study has not been carried out in Japan. A nationwide multicenter study with 512 operative survivors was performed. Actuarial survival rate at 30 years (maximum follow-up) was 98.4%. Fifty-four patients (10.5%) had clinically important arrhythmias, including 23 patients with bradycardia caused by sick sinus syndrome or atrioventricular block (AVB). A patient with complete AVB (CAVB) without pacemaker implantation (PMI) died later. Two patients had sustained ventricular tachycardia (VT) and syncope was reported in 18 patients with ventricular arrhythmias (VA). Atrial tachyarrhythmias were observed in 13 patients. Older age at operation was a risk factor for atrial fibrillation/flutter, longer postoperative survival duration for VA, and QRS duration >120 ms for VT. Perimembranous ventricular septal defect was related to CAVB. Right ventricular outflow patch was not a risk factor. Importantly, 60% of the subjects had QRS duration <120 ms. The prevalence of serious arrhythmias is low in Japanese TOF patients as compared with the results from Western countries. CAVB without PMI and VT are the major risk factors for late morbidity and mortality. The excellent result could be related to the narrow QRS after surgery.

Troponin T and I Expression in Failing and Hypertrophic Heart, and during Normal Development in Human

Background and Objectives:Human Troponin T & I (TnT, TnI has several isoforms which have different functional property. This study was designed to describe the isoform expression of TnT & TnI in failing and hypertrophic human heart and during normal development. Materials and Method:Myocardium was attained from hypertrophic hearts (N=10 of TOF patients who underwent myomectomy, from failing hearts (N=10 of transplant recipients, from normal hearts (N=5 of patients in brain death and from aborted fetal hearts (N=5. After the extraction of RNA, RT-PCR was performed for TnT & TnI isoforms and GAPDH to evaluate the isoform expression qualitatively and quantitatively. Results:In terms of TnI, slow skeletal TnI was expressed more than cardiac TnI in fetal hearts(ratio of Troponin over GAPDH (R=1.3:0.5) but cardiac TnI was dom- inant in adult hearts (R=0.3:1.1 (p<0.05. Failing hearts showed similar pattern with adult hearts (R=0.3: 1.2 and hypertrophic hearts showed the intermediate pattern (R=0.9:1.3. In terms of TnT, T1 and T3 were expressed in fetal hearts (R=0.04, 0.8 but only T3 was expressed in adult hearts (R=1.1. Failing hearts and hypertrophic hearts showed similar pattern with adult hearts and no differences in the amount of expression (R=1.4, 1.3. Conclusion:There is isoform switch from fetal to adult form during development and it might be responsible for the differences of myocardial functional property between fetal and adult heart. Failing and hypertrophic hearts showed no differences with normal hearts, which means the isoform switch of TnT & I might have no significant role in functional disturbances in these conditions. (Korean Circulation J 1998;28 ( ( ( (10 : 1760-1766

Pre- and postoperative arrhythmias in congenital heart disease: from the results of surgery using surface-induced deep hypothermia.

The incidence of arrhythmias in 3614 preoperative patients with congenital heart disease was 1.6 per cent. Pre- and postoperative serial ECGs in 186 patients with an isolated VSD and in 58 patients with TOF were reviewed. The incidence of CRBBB and CRBBB-LAH following VSD repair was 33% and 6.6%, respectively, and for TOF was 55% and 5.2%, respectively. Complete A-V block (CAVB) was seen in 2 patients following VSD repair, and none of TOF patients developed CAVB. Late cardiac or dysrrhythmic death was not recognized in our limited follow up period. The indications for surgery in membranous VSD should be determined more carefully, because the risk of the surgical damage to the conduction system is still higher. Moreover, we must keep in mind that damage to the A-V conduction system may occur naturally even in a patient with small VSD. Finally, it can never be overemphasized that physicians must pay attention to the occurrence and course of postoperative arrhythmias.

Oxygen uptake arterial blood gases and blood lactate concentration during submaximal and maximal exercise in adult subjects with shunt-operated tetralogy of fallot.

Ten female and six male adult subjects with shunt-operated tetralogy of Fallot have been studied at rest and during submaximal and maximal exercise on an average 20 years after the palliative operation. There was a considerable reduction in the aerobic work capacity, maximal oxygen uptake (VO2) being 1.00 1/min STPD. Though ventilation (VE) was out of proportion to VO2 as indicated by an abnormally high ventilation equivalent (52.1), values for VEmax were low (50.81/min BTPS) and of approximately the same order as in a comparable group of totally corrected TOF patients. In spite of increased VE in relation VO2 the PaCO2 increased from 30 mmHg at rest to 49 mmHg during maximal exercise, while PaCO2 decreased from 60 mmHg at rest to 44 mmHg during submaximal exercise I. During heavier exercise no further fall was noted. Base excess decreased from -2.9 to -9.8 mEq/l. Thus a combined respiratory and metabolic acidosis was at hand during exercise, the metabolic component, however, being normal. Maximal blood lactate concentrations were low (5.8 mmol/l) and contrasted with the high intramuscular lactate concentrations earlier reported in some of the patients. The low values found for VO2 max indicate that a palliative operative procedure in TOF is no alternative to an intracardiac repair in the long-term course. The two main factors limiting exercise tolerance were acidosis and accumulation of lactate within the muscle cell.