Modern atrial and ventricular leads for permanent cardiac pacing

Three hundred and fifteen transvenous pacing leads of various modern designs have been assessed over a period of three years. Of these, 103 were implanted in the atrium and 212 in the ventricle. Screw-in leads in the right atrial appendage and short tined leads in the ventricle have resulted in the virtual elimination of lead displacement, and a very low incidence of other lead related problems. In two lead systems it has been found advantageous to have both leads constructed of urethane.

Unsuspected coronary artery disease as cause of chronic atrioventricular block in middle age

Attention has recently been drawn to the relatively poor prognosis of middle aged patients paced for chronic atrioventricular block when age-linked expectation of life is taken into account, and it has been suggested that this may be the result of underlying coronary artery disease, despite the absence of symptoms to suggest this. It was the purpose of this study to determine the incidence of unsuspected coronary artery disease in middle aged patients presenting with chronic atrioventricular block. Studies were made on a consecutive series of 30 patients aged 45 to 65 (mean age 56 years) with chronic atrioventricular disease who had been referred for pacing. Patients presenting with acute myocardial infarction or angina or with sinuatrial disease without atrioventricular disease were excluded. Coronary arteriography disclosed the presence of severe coronary artery disease in 13 patients. Of the remaining 17 patients, four had congestive cardiomyopathy, two had hypertrophic cardiomyopathy, one had aortic stenosis, and in 10 patients the aetiology of the heart block was unknown. Myocardial revascularisation was undertaken in six patients with paroxysmal atrioventricular block caused by coronary artery disease. Operation did not result in any sustained improvement in atrioventricular conduction.

The transport and accumulation of adenine nucleotides during mitochondrial biogenesis

The atractyloside-insensitive accumulation of adenine nucleotides by rat liver mitochondria (as opposed to the exchange-diffusion catalysed by the adenine nucleotide translocase) has been measured by using the luciferin/luciferase assay as well as by measuring [14C]ATP uptake. In foetal rat liver mitochondria ATP is accumulated more rapidly than ADP, whereas AMP is not taken up. The uptake of ATP occurs against a concentration gradient, and the rate of ATP uptake is greater in foetal than in adult rat liver mitochondria. The accumulated [14C]ATP is shown to be present within the mitochondrial matrix space and is freely available to the adenine nucleotide translocase for exchange with ATP present in the external medium. The uptake is specific for ATP and ADP and is not inhibited by adenosine 5'-[beta gamma-imido] triphosphate, GTP, CTP, cyclic AMP or Pi, whereas dATP and AMP do inhibit ATP accumulation. The ATP accumulation is also inhibited by carbonyl cyanide m-chlorophenylhydrazone, KCN and mersalyl but is insensitive to atractyloside. The ATP uptake is concentration-dependent and exhibits Michaelis-Menten kinetics. The divalent cations Mg2+ and Ca2+ greatly enhance ATP accumulation, and the presence of hexokinase inhibits the uptake of ATP by foetal rat liver mitochondria. These latter effects provide an explanation for the low adenine nucleotide content of foetal rat liver mitochondria and the rapid increase that occurs in the mitochondrial adenine nucleotide concentration in vivo immediately after birth.

Inhibition of adenosine triphosphatase, 5-hydroxytryptamine transport and proton-translocation activities of resealed chromaffin-granule 'ghosts'

1. Highly purified resealed chromaffin-granule ;ghosts' were assayed for ATPase and ATP-driven H(+)-translocation and 5-hydroxytryptamine-uptake activities, and for 5-hydroxytryptamine uptake driven by an imposed transmembrane H(+)-gradient. The effects of several inhibitors on these activities were studied. 2. Dicyclohexylcarbodi-imide inhibits all of these activities, but not in parallel; at low concentrations it decreases the permeability of the membrane to protons. 3. 4-Chloro-7-nitrobenzofuran (Nbf-Cl) and silicotungstate inhibit ATP-dependent activities, without effect on 5-hydroxytryptamine uptake driven by an imposed H(+)-gradient. 4. Tributyltin chloride inhibits all of the activities. 5. Treatment of the ;ghosts' with low concentrations of urea inhibits 5-hydroxytryptamine uptake and ATP-dependent generation of a transmembrane H(+)-gradient, without inhibiting ATPase activity. 6. Nbf-Cl and silicotungstate are without effect on the rate of leakage of 5-hydroxytryptamine from preloaded ;ghosts', whereas dicyclohexylcarbodi-imide and tributyltin chloride accelerate the rate of leakage. 7. Treatment of the membranes with (14)C-labelled Nbf-Cl labels several proteins; membranes treated with dicyclohexyl[(14)C]carbodi-imide are labelled predominantly in a protein of low molecular weight, which may be analogous to the mitochondrial H(+)-conducting proteolipid. 8. It is concluded that Nbf-Cl and silicotungstate inhibit the H(+)-translocating ATPase of the granule membrane; that dicyclohexylcarbodi-imide inhibits the ATPase, and inhibits 5-hydroxytryptamine accumulation by accelerating leakage of the amine; and that the effects of tributyltin chloride are due to inhibition of the ATPase, and collapse of the transmembrane H(+)-gradient through OH(-)-anion exchange.

Physiological cardiac pacing

With the availability of reliable transvenous atrial leads and advances in electronic and battery technology, pacing for the restoration of the atrioventricular sequence has become practicable. This paper presents (1) a historical review of physiological cardiac pacing, and (2) a functional description of pacemakers currently available or in clinical validation. The indications and limitations of use for each is discussed on the basis of clinical experience in 176 patients. Predictions are made for future application of sophisticated pacemaker systems after the remaining clinical and technological barriers are overcome.

Hormone-initiated maturation of rat liver mitochondria after birth

1. The injection of adrenaline, glucagon or cyclic AMP into foetal rats in utero initiates the maturation of energy transduction in rat liver mitochondria before birth. 2. The injection of the beta-blocker, propranolol, prevents this maturation process. 3. The maturation of mitochondrial energy transduction is measured in terms of the increase in the respiratory control index and mitochondrial adenine nucleotide concentration. 4. It is postulated that the actions of the hormones, acting through cyclic AMP, affect glycogenolysis and glycolysis to give rise to transient localized high concentrations of ATP. 5. It is the ATP that acts as the molecular trigger, effecting mitochondrial maturation.

Electrophysiological and haemodynamic basis for application of new pacemaker technology in sick sinus syndrome and atrioventricular block

A fundamental description of pacemaker systems which are commercially available or in clinical validation is given as a background for their application in a series of 62 consecutive patients presenting over a period of 1 year for permanent cardiac pacing. The patients (23 (37%) sick sinus syndrome, 38 (61%) atrioventricular block, and 1 ventricular tachycardia) were studied electrophysiologically and haemodynamically to allow the appropriate application of a pacemaker system. In sick sinus syndrome, 8 patients had permanent atrial pacing, 14 ventricular pacing, and 1 atrioventricular sequential pacing; in atrioventricular block, 8 patients had atrial synchronous ventricular inhibited pacing and the remaining 30 had ventricular pacing. A high incidence of atrial fibrillation, 9 patients, and abnormal sinus node function, 15 patients, precluded wider use of atrial synchrony. The results show benefit in acute haemodynamic studies of using systems including atrial sensing and/or pacing, and with greater availability of atrioventricular sequential and still more advanced pacemakers with dual sensing as well as dual pacing the majority of patients may be offered this benefit.

[Systolic time intervals and abnormal left ventricular contraction in coronary heart disease (author's transl)]

Systolic time intervals (STI) were determined in relation to haemodynamic and angiographic data in 72 patients (pts.) with chronic cornary heart disease (CHD). Routine right-and left-heart catheterization was performed with a view to coronary surgery and/or left ventricular (LV) aneurysmectomy. LV and pulmonary pressure were measured before LV and coronary angiography. Non-invasive investigation (not simultaneously done with catheterization) included the registration of phono-and apexcardiogram and the carotid pulse. The following time intervals were averaged over a period of 5 beats: electromechanical systole (QA2), left ventricular ejection time (LVET), pre-ejection period (PEP), electro-mechanical interval (EMI), isovolumetric contraction and relaxation period (IVCT and IVRP), and the ratio PEP/LVET. LV angiography showed normal con-raction in 24 pts., localized dyskinesis in 25 pts., aneurysm in 12 and generalized dyskinesis in another 11 pts. (groups 1-4).

RESULTS

in pts. with chronic CHD, PEP and IVCT are prortionally prolonged (r=0.816***). QA2 and (even more) LVET are shortened. The correlation of LVET and QA2 with heart rate remains significant (p less than 0.005). Prolongation of PEP and IVCT and shortening of LVET and AQ2 increase with the extent of LV contraction abnormality. The degree of STI abnormality correlates with an increase in pulmonary pressure. Shortening of LVET does not correlate with lengthening of PEP. PEP/LVET ratio increases significantly with LV dyskinesis: being 0.394+/-0.085 in pts. with normal contraction, 0.448+/-0.076 with normal contraction, 0.448+/-0.076 with localized dyskinesis, 0.541+/-0.167 with generalized dyskinesis and 0.565+/-0.093 with LV aneurysm. -IVRP is prolonged (to 0.131+/-0.019 sec) without significant differences between the four groups. Non-invasive findings in chronic CHD roughly classify pts. into groups with definite LV contraction abnormality. However, clear estimation of the actual pressure in the (diastolic) LV and in the pulmonary circulation from non-invasive data is of course not possible.

Noninvasive assessment of left ventricular function in chronic heart disease

Externally recorded STI were compared with invasively determined EF in 10 normal subjects and 86 patients with various forms of chronic heart disease. From phono-, apex-, and electrocardiograms and carotid pulse tracings, recorded without rigidly controlled conditions (postabsorptive state, fixed time of day, exclusion of atrial fibrillation, and discontinuation of cardiac drugs), PEP, electromechanical interval, isovolumic contraction period, and LVET were measured and deltaPEP (deviation from predicted normal) and PEP/LVET were drived. EF was determined with biplane angiocardiographic methods. Patients were divided into groups based on pathophysiology and state of clinical compensation. The ability of STI to discriminate abnormal from normal function, as compared with EF, varied with each noninvasive parameter and with each physiologic group. On a group basis, the discriminatory ability of PEP was better than that of other noninvasive parameters studied, but did not always parallel that of EF. PEP also tended to correlate better with EF than the other noninvasive measurements. On an individual patient basis, however, the ability of even PEP to predict EF was poor. It is concluded that the usefulness of assessing left ventricle function in chronic heart disease by STI is limited.

Long-term prognosis after acute anterior infarction with atrioventricular block

The purpose of this study was to evaluate the need for permanent pacing in patients who have survived the effects of anterior myocardial infarction with complete heart block and have returned to sinus rhythm but who are left with impairment of intraventricular conduction. We have reviewed 52 patients with complete heart block complicating recent anterior myocardial infarction. Temporary pacing was instituted in all patients. There were 25 hospital survivors who were followed for an average of 49 months. Long-term pacing was established in 4 patients. Of the 21 patients in sinus rhythm, 14 had partial bilateral bundle-branch block with either right bundle-branch block and left anterior hemiblock or right bundle-branch block and left posterior hemiblock; at the end of the follow-up period, 10 of these 14 were alive and well. Furthermore, permanent pacing failed to prevent sudden death in 2 patients. At the present time, therefore, we conclude that long-term pacing is not justified in patients, otherwise asymptomatic, with partial bilateral bundle-branch block persisting after transient complete heart block in anterior myocardial infarction.

Mitral regurgitation in coronary heart disease

Mitral reguritation is a relatively common finding in coronary heart disease. In this series of 127 patients, selected with a view to coronary or left ventricular surgery on the basis of severity of symptoms, the incidence was 39 (31%). Mitral regurgitation is significantly more common in patients with a history or electrocardiographic evidence of previous myocardial infarction. Clinically it may present as a pan- or late systolic or even a mid-systolic, ejection type murmur at the apex or at the left sternal edge; but in 39 per cent of the patients with angiographic mitral regurgitation no murmur was present. Angiographically important mitral regurgitation (grades 2-4/4) was usually associated with a systolic murmur; this finding was independent of ejection fractions. Left ventricular enlargement clinically or radiographically is likely to accompany mitral regurgitation but left atrial enlargement (electrocardiographically or on chest x-ray) is a more reliable pointer to mitral regurgitation and pulmonary venous hypertension is even more strongly suggestive of its presence. The electrocardiographic signs of papillary muscle infarction were rare in this series (15%) and were not related to angiographic mitral regurgitation. There was no difference in the incidence of mitral regurgitation in association with anterior or inferior myocardial infarction or in distribution of coronary artery disease. There is, however, a higher incidence of mitral regurgitation in more severe coronary arterial disease (P less than 0-05). The incidence of mitral regurgitation is significantly higher with reduction in left ventricular ejection fraction (P less than 0-001), with rise in the left ventricular end-diastolic pressure (P less than 0-02), and with abnormal contraction patterns, but the severity of mitral regurgitation is not significantly related to these findings.

Left ventricular function after aortic valve replacement

Changes in haemodynamics and in systolic time intervals, early after valve replacement, were studied in a group of 15 patients. Though all the haemodynamic measurements were within normal limits at 44 hours after operation, there was a persistent change in systolic time intervals (shortening of left ventricular ejection time and electromechanical systole, and prolongation of pre-ejection period and increase in the ratio PEP/LVET). The effect of periods of myocardial ischaemia during cardiopulmonary bypass on myocardial function is suggested as the explanation for the changes observed.

Hemodynamic effects of verapamil and practolol in man

The hemodynamic effects of verapamil and practolol were investigated in a group of 10 selected patients (7 with coronary artery disease) undergoing cardiac catherization. The drugs were given i.v. in a dose of 0.1 mg/kg, alone or in combination, before and after controling the heart rate by atrial pacing. Measured hemodynamic parameters included aortic and left ventricular pressure and its first derivative, cardiac output, and echocardiographically derived left ventricular dimensions. Each drug given individually caused minor hemodynamic changes, but the combination of practolol and verapamil when the heart rate was fixed by atrial pacing invaribly caused a reduction in LV dp/dt max which was independent of preload and afterload. It is concluded that both drugs have a mildly negative inotropic effect when administered at this dose intravenously to patients with normal or mildly impaired left ventricular function. The myocardial depression was more apparent when practolol preceded verpamil. Caution must be exercised when using these drugs in combination in patients with impaired myocardial function.