Response to exercise in congenital complete atrioventricular block

Exercise capacity in children with isolated congenital complete atrioventricular block: does pacing make a difference?

The management of patients with isolated congenital complete atrioventricular block (CCAVB) has changed during the last decades. The current policy is to pace the majority of patients based on a variety of criteria, among which is limited exercise capacity. Data regarding exercise capacity in this population stems from previous publications reporting small case series of unpaced patients. Therefore, we have investigated the exercise capacity of a group of contemporary children with CCAVB. Sixteen children (mean age 11.5 ± 4; seven boys, nine girls) with CCAVB were tested. In 13 patients, a median number of three pacemakers were implanted, whereas in three patients no pacemaker was given. All patients had an echocardiogram and completed a cardiopulmonary cycle exercise test. Exercise parameters were determined and compared with reference values obtained from healthy Dutch peers. The peak oxygen uptake/body mass was reduced to 34.4 ± 9.5 ml kg(-1) min(-1) (79 ± 24% of predicted) and the ventilatory threshold was reduced to 52 ± 17% of peak oxygen uptake (78 ± 21% of predicted), whereas the peak work load/body mass was 2.8 ± 0.6 W/kg (91 ± 24% of predicted), which was similar to controls. Importantly, 25% of the paced patients showed upper rate restriction by the pacemaker. In conclusion, children with CCAVB show a reduced peak oxygen uptake and ventilatory threshold, whereas they show normal peak work rates. This indicates that they generate more energy during exercise from anaerobic energy sources. Paced children with CCAVB do not perform better than unpaced children.

The effects of an angiotensin-converting inhibitor (enalapril) on patients with mild cardiac failure--evaluating cardiac function based on the relationship between daily walking pace and heart rate

BACKGROUND

Heart failure has been evaluated by several methods, the New York Heart Association (NYHA) classification of heart failure based on symptoms being used most frequently. However, the degree of heart failure assessed by these criteria does not always correlate with cardiac function in daily life.

HYPOTHESIS

The aim of the study was to evaluate cardiac function based on the walking pace/heart rate (HR) relationship to assess the effects of enalapril, an angiotensin-converting enzyme inhibitor, in patients with mild to moderate cardiac function.

METHODS

To evaluate cardiac function objectively, we developed a method using a pedometer to count the steps walked while simultaneously recording HR using a Holter electrocardiograph (ECG). Step-count walk rate (WR) was recorded on the magnetic tape of the Holter apparatus, and both HR and walking pace were calculated automatically by the Holter ECG analysis system. Data were determined every hour, and mean pace and HR were plotted along the x and y axes, respectively. The slope of HR x WR was calculated using the least squares method. The slope and the total number of steps were regarded as indicators of cardiac function and quality of life, respectively. We analyzed 36 subjects, consisting of 8 normal volunteers, 8 patients in New York Heart Association (NYHA) class I. 11 in class II, and 9 in class III chronic mild heart failure, during maximal exercise work load by bicycle ergometer; furthermore, fractional shortening of the left ventricle on echocardiogram was determined in 14 patients with chronic mild heart failure and was compared with the slope of HR x WR. Enalapril was administered at a daily dose of 2.5-10 mg for 1-24 months (mean 6 months) in 60 patients to evaluate the effects of this drug on these parameters.

RESULTS

There was a significant inverse relationship between maximal work load and the HR x WR slope, and also between the fractional shortening and the slope, suggesting that the slope may reflect the severity of cardiac dysfunction. Furthermore, the slope decreased significantly from 1.8 +/- 1.26 before enalapril to 1.0 +/- 0.94 (mean +/- standard deviation) after drug administration, while the total number of steps increased significantly from 4842 +/- 3581 to 7804 +/- 4793.

CONCLUSION

The slope of the graph relating step count and HR proved to be a good, objective indicator of cardiac function, and enalapril therapy improved this parameter.

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

To 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 from 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 patient 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.

Chronotropic competence of the sinus node in congenital complete heart block

Electrocardiograms taken at rest of 2 children with transplacental exposure to anti-Ro antibody but 1:1 atrioventricular conduction demonstrated sinus node disease. Treadmill exercise testing of 28 patients with congenital complete heart block found 3 patients with chronotropic incompetence of the sinus node.

Congenital complete atrioventricular block

The various etiologies, pathologic findings, clinical concerns, and features of congenital complete atrioventricular block are presented and discussed. In addition, prenatal and antenatal diagnostic techniques are explained and analyzed. Lastly, treatment and the issues involved in deciding proper treatment are discussed in such a way that the general pediatrician can help the family to understand and handle the problem.

Cardiorespiratory response to exercise in congenital complete atrioventricular block

In 8 patients aged 8 to 17 years with congenital complete atrioventricular (AV) block, exercise testing was performed on a treadmill. Cardiorespiratory endurance performance was assessed by determination of the ventilatory threshold. The mean value for ventilatory threshold was significantly lower (p less than 0.005) than the normal mean value and averaged 76 +/- 16%, 75 +/- 17% and 75 +/- 16% of the predicted normal value in children of the same sex and comparable age, weight and height, respectively. The ventricular rate at rest varied from 36 to 56 beats/min and increased to a mean value of 106 +/- 25 on exercise. When expressed as a percentage of the normal value, the heart rate was subnormal (below the 95% confidence limit) in all patients, throughout different exercise levels. For the same exercise intensity the oxygen uptake, expressed as ml/min/kg, was significantly lower (p less than 0.02) in patients than in normal individuals. This suggests an inadequate hemodynamic adjustment to the relative exercise bradycardia and a higher than normal anaerobic/aerobic energy supply. Exercise testing was found to be useful in the assessment of congenital AV block, because the resting heart rate did not permit prediction of the relative exercise bradycardia or the degree of exercise intolerance.

Physiologic correlates of the heart rate response to upright isotonic exercise: relevance to rate-responsive pacemakers

Rate-responsive cardiac pacing requires a sensitive physiologic variable that is closely correlated with the heart rate-oxygen uptake relation, particularly in patients with heart failure whose cardiac output response to exercise is more dependent on heart rate. Accordingly, the heart rate response to upright exercise was measured in 81 patients with heart failure or hypertension, or both, and in 27 normal subjects. Oxygen uptake (VO2), minute ventilation (VE), cardiac output, right heart pressures and the mixed venous temperature, oxygen saturation (SvO2) and pH were analyzed throughout exercise. Linear regression analysis of these variables with heart rate revealed the following: 1) There was a highly linear heart rate-VO2 relation in each subject (the average slope of this relation was greater [p less than 0.05] in patients with more severe failure). 2) VE was highly correlated with exercise heart rate, and its slope was not different between normal subjects and patients. 3) Mixed venous temperature and pH were poor predictors of exercise heart rate, particularly at low or moderate levels of work; however, SvO2 was highly correlated with heart rate for all levels of work. Thus, in normal subjects and patients with heart failure or hypertension, or both, heart rate increases linearly with isotonic leg exercise. Minute ventilation and mixed venous oxygen saturation are highly correlated with this response and may serve as potential sensors for rate-responsive pacemakers.

Left ventricular function at rest and during exercise in congenital complete heart block: a radionuclide angiographic evaluation

This study evaluates intrinsic cardiac performance during upright exercise in patients with congenital complete heart block. Left ventricular ejection fraction and volume were measured at rest and peak upright exercise with radionuclide angiography in 5 patients aged 11 to 39 years with congenital complete heart block: 4 were in New York Heart Association class I and 1 was in class II. The resting cardiac output was maintained at a normal level by an increase in end-diastolic volume rather than by a decrease in end-systolic volume. The left ventricular ejection fraction was normal at rest in all patients, but an abnormal response to exercise was noted in 3 patients. There was no appreciable change in the end-diastolic volume during exercise. Thus, patients with congenital complete heart block utilize the Starling mechanism to maintain normal resting cardiac output, but the response to exercise is usually abnormal even in the absence of symptoms.

Central venous oxygen saturation for the control of automatic rate-responsive pacing

A rate-adjusting pacemaker system is described which uses central venous oxygen saturation (SO2) for the regulation of the pacing rate. This system was tested externally in ten patients with chronically implanted VVI units. There was an average increase in cardiac output of 18% with the SO2-regulated pacemaker as compared to the situation during fixed rate stimulation. Central venous oxygen saturation appears to be an ideal biological parameter for autoregulating the pacing rate. It represents the only sensor suitable for the realization of a closed feedback loop concept.

Congenital complete atrioventricular block: clinical and electrophysiologic predictors of need for pacemaker insertion

Because of initial Adams-Stokes attack in the patient with congenital complete atrioventricular (A-V) block may sometimes prove fatal, there is a need to be able to identify the patient at great risk of having such attacks. Twenty-four children with congenital complete A-V block were followed up for 1 to 19 years to determine the efficacy of current methods of predicting risk for Adams-Stokes syncope and the usefulness of pacemaker therapy in relieving symptoms. The heart rate at rest, configuration of surface electrocardiographic complexes, data obtained during intracardiac electrophysiologic study and response to graded treadmill exercise testing were compared in children with and without syncope. One or more Adams-Stokes episodes were experienced by eight children, one of whom died. Only a persistent heart rate at rest of 50 beats/min or less demonstrated any significant (probability [p] less than 0.01) correlation with the incidence of syncope. Intracardiac electrophysiologic study was of little benefit because of site of block did not correlate with syncope. Although the increase in heart rate during treadmill exercise testing showed no correlation with prevalence of syncope or location of block, exercise-induced ventricular ectopic beats may have predictive value in older children and young adults. Ventricular pacemakers were implanted in 10 children. Each child was asymptomatic over a 1 to 10 year follow-up period. Because extreme bradycardia may contribute to the prevalence of Adams- Stokes attacks in children with congenital complete A-V block, careful evaluation of heart rate at rest may be an effective means of differentiating patients at risk of syncope. Pacemaker therapy is a feasible and effective method of treatment in young children and relieves symptoms

Exercise-induced ventricular ectopy in children and young adults with complete heart block

Twenty-five children and young adults with complete heart block and 50 normal control subjects were maximally exercised on a treadmill and their electrocardiograms were analyzed for the presence and degree of ventricular ectopy activity. Sixty-eight % (17 of 25) of the heart block patients and significant ventricular ectopy (frequent unifocal ectopy or worse) on exercise compared to 2% (one of 50) of the controls (p = less than 0.01). In the patients with block there was a significant trend toward more frequent and more severe ectopy with increasing age (p = less than 0.05) independent of heart rate. More severe ventricular ectopy was also seen in those patients with QRS prolongation (p = less than 0.05). No significant differences were found between the 14 patients with isolated "congenital" heart block, the seven with associated defects, and the four with surgically acquired block. We believe that severe ventricular ectopy is common at exercise in patients with complete heart block and they may have an increased risk for sudden death.

Graded exercise testing in patients with sinus node dysfunction

Serial measurements of heart rate and oxygen uptake were obtained before and during maximal upright graded bicycle stress testing in 16 patients, 10 to 77 years old (mean 46 years), with sinus node dysfunction; five had permanent and two had temporary demand ventricular pacemakers. In 15 patients, including those with pacemakers, maximal exercise was performed before and after the intravenous administration of 1 mg atropine. Maximal exercise was terminated because of cerebral symptoms in seven (three had effort-induced tachyarrhythmias and one had autonomic insufficiency), fatigue in five (one had effort-induced heart block), heart failure in three and angina pectoris in one. With maximal exercise, patients with sinus node dysfunction were unable to obtain maximal heart rates or oxygen uptakes comparable to age- and sex-matched control subjects. Additionally, maximal oxygen uptake did not differ significantly between patients with or without pacemakers even when ventricular pacing rates were increased (two instances). The administration of atropine increased the resting heart rate, but the maximal heart rate and oxygen uptake achieved during maximal exercise did not differ significantly from those obtained before the administration of atropine in the patient and control groups. Physically active patients with sinus node dysfunction have diminished exercise capacity due in part to cardiac arrhythmia, latent or overt cardiac failure, or autonomic dysfunction.

Multiple arrhythmias detected during nocturnal monitoring in patients with congenital complete heart block

Twenty patients with congenital complete heart block (CHB) were monitored with ECG tape recordings while awake and asleep. Episodes of marked ventricular slowing during sleep (R-R greater than 3000 msec., i.e. less than 20 beats/min) were noted in 35% (7/20). Most of these sudden R-R prolongations were 2:1 or 3:1 exit block of the junctional focus. Atrial and ventricular rate changes were mostly concordant in 2/3 but the remainder demonstrated fixed ventricular rates while atrial rates varied normally, suggesting a "sick" or "lazy" junctional focus. Other arrhythmias were found in 60% (12/20), including several types of rhythms in three patients. One child with previously unsuspected superimposed multiple arrhythmias later had a syncopal episode despite proven supra-Hisian block. The multiple patterns of atrial and ventricular rate changes found indicate complex feedback mechanisms, suggesting that congenital CHB is not a single entity. Since a significant number of patients demonstrated one or another of these unexpected and potentially hazardous findings, we recommend that congenital block patients be carefully studied, including Holter monitoring done on a regular basis.

Six cases of congenital complete heart block followed for 34-40 years

Images

The relation of heart rate to cardiovascular dynamics. Pacing by atrial electrodes

Hemodynamic studies were carried out as heart rates were controlled by atrial pacing on 10 normal patients at rest and during exercise. Each patient served as his own control. In both states tested the cardiac index, left ventricular work, and peripheral resistance were not significantly altered by changes in heart rate. The stroke index and mean systolic ejection rate decreased linearly with heart rate. During exercise the cardiac index increased up to 98% and again remained constant at all paced heart rates tested. At comparable heart rates the tension-time index, left ventricular work, stroke index, and mean systolic ejection rate were higher during exercise than at rest. At comparable heart rates [see figure in the PDF file] peripheral resistance was 38% lower during exercise than at rest. Myocardial oxygen consumption, as inferred from the tension-time index, increased with heart rate in both states.