Does parallel conductance vary during systole in the human right ventricle?

OBJECTIVES: Right ventricular (RV) contractile performance remains poorly characterised, particularly in humans. Conductance catheter techniques have the potential to overcome the geometric difficulties in RV volume measurement that have hindered systematic studies of RV pressure volume relations. The present study examines changes in parallel conductance (Vc) that may occur during the cardiac cycle in the human right ventricle. METHODS: Using signals obtained from custom-built conductance catheters, six isochronal systolic values of Vc (Vc(t)) were measured during hypertonic saline wash-in. Studies were performed in nine patients undergoing right heart catheterisation. Their ages ranged from 7 to 39 years (median = 16) and their weights ranged from 20.3 to 84.7 kg (median = 50.0 kg). Measurements of mean Vc and isochronal Vc(t) and its variability during systole were assessed. Mean Vc was measured using the Baan technique (Vc(Baan)), Vc(t) was measured from six systolic isochrones obtained during the same period of hypertonic saline wash-in. RESULTS: The temporal changes in Vc(t) were small (mean 5.8%, median = 4.4%, range = 0.6-17.9%) of total corrected end-diastolic volume (mean maximal variation of 7.7 ml). The value of Vc(t) obtained at dp/dtmax (mean = 99.1 ml; median = 104.75 ml; range 20.15-196.7 ml) was not significantly different to that obtained at dp/dtmin (mean = 100.0 ml; median = 110.87 ml; range = 20.0-204.2 ml) (P > 0.05), but both were higher than the single Vc measurement (Vc(Baan)) obtained using the standard approach (P = 0.02). The correlation between Vc(Baan) and Vc(t) for group data; (Vc(Baan) = 89.69 ml, s.d. = 43.73 ml; Vc(t) = 98.16 ml, s.d. = 50.16 ml) produces a regression slope of 0.99 for all studies (P = 0.02). CONCLUSION: We conclude that parallel conductance does vary during systole in the human right ventricle of adults and older children after repair of congenital abnormalities but there is no significant difference in Vc(t) at dp/dtmin and dp/dtmax. However, there was a significant difference when the isochronal Vc(t) measurement is compared with the standard single value technique (Vc(Baan)) obtained using the hypertonic saline wash-in method. The excellent correlation between Vc(t) and Vc(Baan) suggests that the correction of Vc for the phase of the cardiac cycle is unnecessary for most purposes when studying the human right ventricle.

Validation of a new intraoperative technique to evaluate load-independent indices of right ventricular performance in patients undergoing cardiac operations.

BACKGROUND: Assessment of right ventricular performance in the perioperative period is difficult because there is no generally accepted method of measuring right ventricular volume. We set out to determine whether conductance technology could provide a valuable technique for the investigation of intraoperative right ventricular function. METHODS AND RESULTS: Three validating studies were performed in 25 patients undergoing routine coronary revascularization. Study 1: The influence of conductance catheter position in the right ventricle was examined in 10 patients. Insertion of the conductance catheter through the outflow tract was associated with a larger gain constant and a smaller parallel conductance compared with insertion through the tricuspid valve. Study 2: The reproducibility of contractility measurements with the use of a conductance catheter was examined in 7 additional patients. Removal and reinsertion of the conductance catheter was not associated with any significant difference in right ventricular volume or contractile function. Study 3: Right ventricular performance before and after cardiopulmonary bypass was compared in 8 additional patients. There was a fall in the slope of the right ventricular preload recruitable stroke work from 15.6 (3.8) to 11.0 (5.1) mm Hg (P=.01) and an increase in the slope of the end-diastolic pressure-volume relations from 0.05 (0.02) to 0.11 (0.05) mm Hg/mL (P=.001). CONCLUSIONS: The conductance technique can be used to study perioperative changes in right ventricular performance. Insertion of the conductance catheter through the outflow tract provides stable and reproducible data. There is significant impairment of right ventricular contractility in the early postoperative period.

The effects of short-term hypertensive left ventricular hypertrophy on intracellular pH and intracellular electrolytes in rats.

Experiments were performed to assess the effect of left ventricular hypertrophy (induced by experimental hypertension) on intracellular pH (pHi) and intracellular electrolytes in left ventricular tissue. They were undertaken on: (1) hypertensive rats (hypertension being induced by either: (a) subdiaphragmatic aortic constriction, (b) unilateral renal artery clipping, or (c) unilateral renal artery clipping with contralateral nephrectomy); (2) sham-operated rats for the above 3 subgroups; and (3) control (unoperated) rats. Intracellular pH and intracellular electrolytes were measured in left ventricular, right ventricular and skeletal muscle tissue from these animals. Intracellular pH control was assessed by exposing a number of animals in each group to an acute respiratory acidosis (by varying the concentration of inspired PCO2). In association with left ventricular hypertrophy (secondary to hypertension), left ventricular pHi became significantly alkaline in all experimental hypertensive groups compared with control values; pHi control (in response to an acidosis) was also significantly improved. There was no change in resting levels of pHi or pHi control in right ventricular or skeletal muscle tissue in any hypertensive group. There was no change in resting levels of pHi or pHi control in left ventricular, right ventricular or skeletal muscle tissue from sham-operated animals. This suggests that these changes are the result of hypertrophy per se, rather than due to a generalised mechanism secondary to hypertension and operating on all tissues. There was no change in intracellular electrolyte concentration or content in association with hypertension in any tissue or group studied.

The effects of long-standing hypertensive left ventricular hypertrophy on intracellular pH and intracellular electrolytes in rats.

Experiments were performed to assess the effect of long-standing (4-8 weeks) left ventricular hypertrophy (induced by experimental hypertension) on intracellular pH (pHi) and intracellular electrolytes in left ventricular tissue. They were undertaken on: (1) hypertensive rats (hypertension being induced by either (a) subdiaphragmatic aortic constriction, (b) unilateral renal artery clipping, or (c) unilateral renal artery clipping with contralateral nephrectomy); (2) sham-operated rats for the above 3 subgroups; and (3) control (unoperated) rats. In this study the hypertension (and therefore the hypertrophy) was of long (4-8 weeks) duration. Intracellular pH and intracellular electrolytes were measured in left ventricular, right ventricular and skeletal muscle tissue from these animals. Intracellular pH control was assessed by exposing a number of animals in each group to a respiratory acidosis (by varying the concentration of inspired PCO2). As described previously [Oldershaw PJ, Cameron IR, Int J Cardiol 1988;18:131-141], in the earlier stages of left ventricular hypertrophy (1-4 weeks duration) left ventricular pHi was significantly alkaline at normal levels of extracellular pH. At this late stage, with the exception of animals with aortic constriction, pHi had returned to control values. There was no change in resting levels of pHi in right ventricular or skeletal muscle tissue in any hypertensive group. The improved control of pHi in left ventricular tissue observed with hypertrophy of short duration (1-4 weeks [Oldershaw PJ, Cameron IR. Int J Cardiol 1988;18:131-141]) persisted in all experimental groups at this stage (4-8 weeks) after the onset of development of left ventricular hypertrophy. There was no change in pHi control in right ventricular or skeletal muscle tissue. Neither was there any change in intracellular electrolyte concentrations or content in association with hypertension in any tissue or group studied.

In vitro buffering capacity of cardiac and skeletal muscle tissue in normotensive and hypertensive rats. Assessment using PCO2 equilibration of homogenates.

Experiments were performed to assess the in vitro buffering capacity (physicochemical buffering) of cardiac and skeletal muscle tissue in normotensive and hypertensive rats using the techniques of PCO2 equilibration of tissue homogenates. We have previously shown (Oldershaw PJ, Cameron IR. Int J Cardiol 1988;18:131-141 and Int J Cardiol 1988;18:143-149) that the ability of myocardial cells to regulate intracellular pH is improved in association with left ventricular hypertrophy (induced by experimental hypertension) and this study purports to investigate the role of physicochemical buffering in this improved control. Rats were made hypertensive using the technique of sub-diaphragmatic aortic constriction and left for 1 or 4 weeks at which time samples of left ventricular and skeletal muscle tissue were taken for analysis; sham-operated animals were used as controls. The tissue was homogenised and in vitro buffering capacity assessed using PCO2 equilibration. The slope of the log PCO2-pH plot was calculated for each tissue and taken as a measure of buffering capacity. In control animals, in vitro buffering was greater in skeletal than cardiac muscle (slopes 1.89 +/- 0.5 cf. 1.64 +/- 0.06 P less than 0.05). In association with hypertension of 1 or 4 weeks duration the buffering capacity of left ventricular tissue increased to 2.00 +/- 0.08 (P less than 0.01) at 1 week and to 2.05 +/- 0.06 (P less than 0.01) at 4 weeks. There was no comparable change in the buffering capacity of skeletal muscle tissue. At least part of the observed in vivo changes in intracellular pH control may therefore be explicable on the basis of improved intracellular physicochemical buffering.

Left ventricular dysfunction in obstructive lung disease: an echocardiographic and angiographic study of cor pulmonale patients with decreased mitral E-F slope.

Twenty-nine patients with cor pulmonale were investigated by echocardiography and cardiac catheterisation in order to assess the significance of a reduced mitral E-F slope. Seven patients had coronary arterial disease and were therefore excluded from further analysis. Of the remaining 22 patients, 15 had a reduced mitral E-F slope but an otherwise normal mitral valve on echocardiography. They were found to have an increased left ventricular end-diastolic pressure measured at cardiac catheterisation when compared to the other seven patients with cor pulmonale and a normal E-F slope. The patients with a reduced E-F slope had an increased mean right ventricular internal dimension and interventricular septal thickness measured echocardiographically when compared to the patients with a normal E-F slope. Right ventricular dysfunction was suggested in these patients by an increased right ventricular end-diastolic pressure measured at cardiac catheterisation. We discuss possible mechanisms of left ventricular dysfunction and of intracardiac pressure transmission in cor pulmonale, and the implications of these mechanisms for effective management.

Left atrial myxoma infected with Streptococcus viridans.

A case is described of Streptococcus viridans endocarditis involving a left atrial myxoma. The diagnosis was made by echocardiography and the infected tumour was successfully treated by surgical removal. A review of the published literature about left atrial myxomas underlines the importance of performing echocardiography in all patients with suspected endocarditis.

Diagnostic features of localised pericardial constriction.

We report a case of localised pericardial constriction leading to right ventricular outflow tract obstruction. Localised pericardial constriction is rare, but the diagnosis should be considered in patients who present with recurrent pericardial constriction following previous partial pericardiectomy. Close attention to physical findings may enable the diagnosis to be made prior to cardiac catheterisation.

Guillain-Barré syndrome following cardiopulmonary bypass.

Two cases of Guillain-Barré syndrome occurring after otherwise uneventful cardiac surgery using cardiopulmonary bypass are presented. Although Guillain-Barré syndrome has been reported after surgical procedures, it has never been reported after cardiopulmonary bypass. Recent literature supports an immune mediated process for Guillain-Barré. Cardiopulmonary bypass may act as the trigger for this immune mediated response.

The clinical features, management and outcome of persistence of the arterial duct presenting in adult life.

We have reviewed the 25 patients who, between 1973 and 1988, presented to the Brompton Hospital in adulthood with persistence of the arterial duct (ductus arteriosus). As pulmonary arteriolar resistance is the main determinant of management and prognosis in this condition, the patients were divided into groups with either normal or mild elevation of resistance (less than 10 units/m2: 19 patients) or with severe elevation (greater than 10 units/m2: 6 patients). Patients with normal pressures or mild elevation tended to be older (mean age 45 years). Many (70%) were asymptomatic, but dyspnoea with signs of left heart failure was the commonest presenting complaint. Surgical closure of the duct was performed in 16 with good result in all. Survival for the entire group, however, was long. There was a symptomatic indication for surgery (due to hyperdynamic circulation) in 5. In those with severely elevated pulmonary arteriolar resistance, the mean age of presentation was 31 years and the survival short. The commonest presenting symptom was dyspnoea. Surgical closure of the duct was attempted in two patients but with a poor outcome in both. All patients with an elevated resistance had developed this complication by the third decade of life. Significant elevation was not a feature of older patients, suggesting that, in this age group, the risk of elevation is slight. Surgery, nonetheless, may be indicated for relief of symptoms due to a large systemic to pulmonary shunt.

Plasma brain natriuretic peptide concentrations in patients with chronic mitral regurgitation.

BACKGROUND AND AIMS OF THE STUDY: Patients with chronic mitral regurgitation (MR) are often referred for surgery only after irreversible left ventricular (LV) dysfunction has developed. Our aim was to determine whether plasma brain natriuretic peptide (BNP) concentrations could serve as a marker for early LV dysfunction in this condition. METHODS: Twenty-two patients with isolated chronic MR and echocardiographic evidence of at least moderate regurgitation were studied. RESULTS: Plasma BNP concentrations were significantly higher in patients than in normal volunteers (20.85 +/- 16.9 versus 3.37 +/- 0.9 pmol/l; p = 0.007). Concentrations increased with increasing severity of symptoms and were highest in those in NYHA class IV, but did not correlate with LV dimensions, fractional shortening or left atrial size. Of note, two asymptomatic patients with high BNP concentrations were referred for surgery within the 12-month follow up period due to symptom progression. CONCLUSIONS: Plasma BNP concentrations are elevated in most patients with isolated chronic MR, including those who are asymptomatic with normal LV dimensions. The significance of these findings is uncertain, but they suggest that changes in ventricular physiology occur early in the disease process and before they can be detected echocardiographically. Longitudinal studies are required to determine if patients with high BNP levels have an adverse prognosis and if this can be altered by earlier surgical intervention.

Effects of age-related changes in cavity size, wall thickness and heart rate on left ventricular function in normal children.

In this study the effects on left ventricular function of age-related changes in left ventricular diameter, wall thickness, and heart rate were assessed in normal children from 1-12 years of age using echocardiography.

Echocardiographic appearances of right atrial thrombus.

A 17-year-old male presented with a four-day history of increasing shortness of breath and right basal pleuritic chest pain. Physical examination revealed central and peripheral cyanosis, sinus tachycardia, elevation of central venous pressure, hypotension, and added third heart sound. Echocardiography (M-mode and two-dimensional) showed a highly mobile mass in the right atrium apparently attached to the interatrial septum. A diagnosis of right atrial myxoma with pulmonary embolization was made and urgent surgery advised. At operation a string of thrombus in the right atrium (presumed from peripheral venous site) occluding a patent foramen ovale was found. The usefulness of echocardiography in diagnosing atrial thrombus and in differentiating clot from tumor is discussed.

Migration of retained pacemaker electrodes.

Two cases of migration of retained pacemaker electrodes are described. The first presented as an unusual cause of deep vein thrombosis while the second was asymptomatic and detected by routine chest x-ray. Both made a good recovery, the first with surgery and the second with the fragment left in situ. A review of the world literature revealed only 13 other such cases. Of the total of 15 cases four are known to have died. In these patients no relationship was found between morbidity and the site of migration or associated infection and/or thrombosis. However surgical treatment appeared to be associated with a better prognosis.

Ten-year experience of 359 epicardial pacemaker systems: complications and results.

In the last ten years (1970-1980) 457 patients underwent permanent pacemaker insertion in the Brompton Hospital. Our practice has been somewhat atypical in that the majority of these patients had epicardial leads, initially using a Cordis intramural sutured electrode (85 patients), and subsequently a Medtronic sutureless electrode (274 patients). Our initial experience with these electrodes was satisfactory, but more recently it has become apparent that the long-term morbidity and complication rate is high. The respective complication rates being 25% and 18% for sutured and sutureless epicardial electrodes. In this study, lead complications were defined as those requiring lead replacement, and problems most commonly encountered were high voltage threshold, infection, and lead fracture. Unless there are specific indications for epicardial pacing it is now our policy to treat patients requiring permanent pacing with endocardial systems. Our complication rate with this technique (90 patients) is significantly lower (9%).

Left main coronary artery stenosis: experience of 93 patients.

The clinical and angiographic findings in 93 consecutive cases of significant (greater than or equal to 50%) obstruction of the left main coronary artery were studied. This lesion was found in 6.85% of patients who underwent coronary arteriography. 93.5% of patients had presented with angina pectoris, of which 28% had unstable angina. There was one catheter-related death. Follow-up data were available in 90 cases, of which 23 were treated medically. Poor left ventricular function and significant right coronary artery disease adversely influenced the outcome in this group. 67 patients had aortocoronary saphenous vein bypass grafting. The operative mortality was 18% overall, but 36% in those undergoing emergency surgery (within 48 hours of catheterisation). Poor left ventricular function and electrocardiographic evidence of previous inferior myocardial infarction were associated with poor operative survival. The 55 survivors of surgery had an excellent prognosis with an annual attrition rate of 4% over two year follow-up period. 87% were asymptomatic at follow-up.

The results of surgery for active endocarditis of the native aortic valve.

Between 1968 and 1981, 40 patients with active endocarditis of the native aortic valve were treated by aortic valve replacement (A.V.R.). There were 8 postoperative deaths (hospital mortality 20%). This included 5 patients who had developed cardiogenic shock prior to surgery. Antibiotic treatment for less than one week and positive cultures on the excised valve had poor prognostic implications but tended to be associated with irreversible haemodynamic failure. Twenty five patients underwent A.V.R. following the onset of severe pulmonary oedema. The hospital mortality in this group was 28% and the 5 year actuarial survival 56% (+/- 11%). Fifteen patients who had developed premature closure of the mitral valve (P.C.M.V.) on M-mode echocardiography but who had no overt signs of cardiac failure underwent A.V.R. with a single death (7% hospital mortality). The 5 year actuarial survival in this group was 87% (+/- 9%). P.C.M.V. is a useful prognostic sign identifying those patients with endocarditis on the native aortic valve likely to benefit from early surgery.

Dissection of the thoracic aorta. A comparison between medical and surgical treatment.

We have reviewed 113 patients with acute thoracic aortic dissection seen between 1965 and 1979. There were no "diagnostic" symptoms or signs of acute dissection, and diagnosis could only be reliably made by aortography. The latter also allowed typing of the dissection (De Bakey classification) which permitted appropriate therapy to be instituted. Aortography should be performed early because of the high mortality of this condition within the first 24 hours. Early surgery is warranted in all patients with Type I dissection since it significantly increases long term survival: 40% 5 year-survival for surgical treatment compared with 13% survival for medical treatment (p less than 0.01). There is no significant difference in long or short term survival for patients with Type III dissection whether patients are treated medically or surgically.

The management of prosthetic valve endocarditis.

During the period 1970 to 1980 2,945 patients underwent valve replacement at the Brompton Hospital. Thirty-one (1%) patients subsequently developed prosthetic valve endocarditis (P.V.E.). Twenty-one (0.7%) patients developed endocarditis within two months of valve replacement. Ten patients were treated medically, with seven deaths, whilst four of the eleven surgical cases died. There were ten cases of late P.V.E. occurring between two months and eight years after initial valve replacement (0.12% per annum). Eight patients were treated surgically, with two deaths, whilst both medical cases died. Thus 67% patients were effectively treated by immediate valve replacement, whilst only 25% medical cases survived. Actuarial survival curves predict a 41% five-year survival following surgery for P.V.E. We stress the importance of early diagnosis of this condition and recommend immediate valve replacement in all patients with P.V.E. developing signs of haemodynamic failure.

Long-term survival following left ventricular aneurysmectomy.

Ninety-four patients who underwent left ventricular aneurysmectomy between 1971 and 1980 are reviewed. In thirty-four cases this operation was combined with myocardial revascularisation. The overall hospital mortality was 6% with a five-year survival of 72% +/- 6%. Symptomatology dominated by dyspnoea, a raised left ventricular end diastolic pressure (L.V.E.D.P.) and ventricular dysrhythmias adversely affected survival. Combined myocardial revascularisation did not affect the hospital mortality but was associated with a trend toward improved long-term survival in two groups of patients viz those presenting with predominant angina and those with major stenoses of two or more coronary arteries. Fifteen patients agreed prospectively to post-operative cardiac catheterisation. Despite symptomatic relief no improvement in L.V.E.D.P. or ejection fraction was demonstrated in this group.