Electrophysiologic and hemodynamic actions of diltiazem: disparate temporal effects shown by experimental dose-response studies

Diltiazem (DT), a potent slow channel blocker, has been found to be clinically useful for treatment of coronary vasospasm, hypertension, and tachyarrhythmias. Nevertheless, only limited data are available on the hemodynamic and electrophysiologic effects of DT. Atrial, His, right ventricular apex, aortic, and Swan-Ganz thermodilution catheters were used in 10 anesthetized dogs, and recordings were made during control period and after each of four infusions of DT (0.01, 0.02, 0.04, and 0.08 mg/kg/min) each lasting 30 minutes. Results showed that heart rate, pulmonary capillary wedge pressure, stroke volume, and HV interval did not change significantly. However, two dogs had second-degree AV block and a third had escape junctional rhythm during DT 0.08 mg/kg/min. Mean aortic pressure (AP), corrected sinus node (SN) recovery time, and systemic vascular resistance (SVR) were significantly reduced, whereas AH interval, AV functional and effective refractory periods were prolonged by DT. AV nodal refractory periods and AH interval were the only parameters significantly affected at DT 0.02 mg/kg/min. SN recovery time was significantly shortened at DT 0.04 mg/kg/min, whereas AP and SVR tell significantly at DT 0.08 mg/kg/min. DT had significant electrophysiologic effects at low doses, whereas hemodynamics were significantly altered only at high doses. Further, major electrophysiologic effects were on the AV node with lesser effects on SN function. Therefore, at a dose when antiarrhythmic effects are evident, the safety of diltiazem is corroborated by lack of adverse hemodynamic effects.

Effects of thiopentone on cardiac performance, coronary hemodynamics and myocardial oxygen consumption in chronic ischemic heart disease

Thiopentone was administered as induction agent for general anesthesia to eight patients with stable ischemic heart disease; 6 mg/kg of the drug induced decrease in arterial blood pressure (-27%), systematic vascular resistance (-20%), stroke volume index (-14%), mean pulmonary arteriolar occlusion pressure (-15%) and left ventricular stroke work index (-38%), while heart rate increased by 10% and cardiac output remained unchanged. Total body oxygen consumption decreased by 30%. Myocardial oxygen consumption decreased by 39% with unchanged or decreased myocardial oxygen extraction and myocardial lactate uptake decreased by 40%. Arterial and coronary sinus hypoxanthine levels were unchanged and no ST-T-segment changes or dysrhythmias were recorded. In the present experimental setting, the results indicate that thiopentone substantially decreased myocardial oxygen requirements. In spite of the marked reduction in coronary perfusion, myocardial oxygen demand was matched by supply, myocardial dysoxia was not induced and cardiodepression was clinically negligible. Rate pressure product was a poor indicator of changes in myocardial oxygen consumption after thiopentone administration.

Hemodynamic and cardiometabolic effects of infrarenal aortic and common iliac artery declamping in man--an approach to optimal volume loading

Nineteen patients undergoing abdominal aortic aneurysm surgery were randomly assigned to two groups and investigated to elucidate the mechanisms of declamping hypotension. The control group of nine patients was kept at an average mean pulmonary artery occlusion pressure (MPAOP) of 11 mmHg (1.46 kPa) before declamping. The other group was volume loaded to a MPAOP of 16 mmHg (2.13 kPa) shortly before declamping. Following declamping there was a significantly greater decrease in mean arterial pressure in the control group, with the same reduction of MPAOP in both groups. In parallel, cardiac and stroke volume indices decreased in the control patients, but remained unchanged in the volume-loaded patients. In the control group there was a reduction in myocardial substrate utilization which was not seen in the volume-loaded patients. No signs of myocardial ischemia could be demonstrated in any of the groups. The results indicate that mismatching between intravascular volume and blood volume is the main cause of infrarenal aortic or common iliac artery declamping hypotension. Volume loading before declamping to a slightly elevated MPAOP can effectively prevent hypotension, while a normal MPAOP does not guarantee a stable hemodynamic situation after declamping.

Regional 99m technetium diphosphonate uptake in experimental dog heart infarct: relation to duration and severity of ischaemia

Regional uptake of 99mTechnetium diphosphonate was compared with regional myocardial blood flow 6, 12 and 24 h after the onset of myocardial infarction in dogs, and with regional creatine kinase depletion 24 h after the onset. Uptake of the imaging agent increased from 6 to 24 h, but no consistent relationship could be demonstrated between regional myocardial blood flow and regional uptake of the diphosphonate nor between uptake and regional creatine kinase depletion at the centre or border of the infarct. In addition, inappropriately high levels of 99m Technetium uptake could be demonstrated in the epicardial layer of the normal tissue surrounding the infarct. We conclude that diphosphonate uptake is not quantitatively related to the severity of ischaemia, and that use of this substance for imaging may over-estimate myocardial infarct size.

Effect on survival after myocardial infarction of long-term treatment with phenytoin

A prospective, randomised, open trial was performed in 150 patients to test for any beneficial effects on 2-year mortality of long-term antiarrhythmic therapy with phenytoin in patients with acute myocardial infarction. Patients were stratified according to age, sex, past history of myocardial infarction, and the presence of absence of electrical or mechanical complications in the course of acute infarction. They were then randomised to treatment or control groups (74 v. 76). The former received phenytoin in doses aimed at maintaining plasma phenytoin levels between 40 and 80 mumol/litre. All patients entered the study before discharge from the coronary care ward. Plasma phenytoin levels were in the therapeutic range in between 51 and 75 per cent of subjects at any follow up visit. There were 19 withdrawals from the treatment group, 10 of which were the result of side effects. There were 5 withdrawals from the control group. According to the original intention to treat, there were 18 deaths at 2 years in the treatment group and 14 deaths in the control group. There was no reduction in the incidence of instantaneous or sudden deaths. Deaths on treatment were not associated with a low phenytoin plasma level. Phenytoin treatment showed no beneficial effects on mortality and was associated with a high incidence of side effects.

The effect of glucose-insulin-potassium on experimental myocardial infarction in the dog

The effect of glucose-insulin-potassium (GIK) infusions was studied in 45 dogs after left anterior descending coronary artery ligation. GIK caused a modest increase in lactate concentration in small veins draining the infarct but did not affect glucose uptake. No effect on creatine kinase activity in the infarct was seen from GIK, although there was a slight increase in blood flow to the centre of the infarct. We concluded that GIK did not reduce infarct size in this experimental model.

Reduction of enzyme levels by propranolol after acute myocardial infarction

The effect of propranolol (0.1 mg/kg intravenously followed by 320 mg given over 27 hour orally) on serum levels of creatine kinase enzyme was studied in a randomized trial involving 95 patients seen within 12 hours of onset of symptoms of uncomplicated myocardial infarction. In 15 patients who were treated with propranolol within 4 hours of onset, and who eventually developed pathological Q waves, peak measured enzyme levels were 27% (P less than 0.0125) lower than in 19 control patients who were also seen within 4 hours of the onset but had no specific treatment. Total calculated enzyme appearance was also lower in the treated patients (reduced 25%, P less than 0.05) as was the calculated rate of the appearance (33%, P less than 0.005). No significant difference was found for treated compared with control patients entering the trial more than 4 hours after the onset of chest pain. This evidence suggests that propranolol may reduce the size of uncomplicated infarctions if it is given intravenously within 4 hours of the onset.

Failure of high doses of propranolol to reduce experimental myocardial ischemic damage

Myocardial creatine phosphokinase (CPK) activity and myocardial blood flow (MFB, 15 +/- mu microspheres) were measured at 24 hours after ligation of the left anterior descending coronary artery in nine untreated anesthetized dogs, in eight dogs pretreated with intravenous propranolol 5 mg/kg and in eight which had both pretreatment as well as infusion of propranolol (1.25 mg/kg/hour) after occlusion. Loss of CPK activity from the border and center zones of the myocardial infarct was similar in extent in dogs which had pretreatment but no infusion of propranolol as it was in the control group. Loss of CPK from the center zone was greater (P less than 0.005) in dogs receiving pretreatment followed by constant infusion of the drug. Propranolol had no significant effect on collateral blood flow to the border or center zone of the infarct. In separate experiments, there was no important difference in hemodynamic measurements, except a slower heart rate (P less than 0.01), when pretreated dogs were compared with control dogs up to 2 hours after coronary ligation. We conclude that propranolol given in this dose does not influence nyocardial damage, on the basis of regional myocardial blood flow or tissue CPK depletion values at 24 hr after coronary occlusion.

Acute myocardial infarction in women. The influence of age on complications and mortality

The prognostic implications of a past history of ischaemic heart disease, site of infarction, ectopic ventricular dysrhythmias (ventricular premature beats (VPB) more than one in 10 sinus beats, and/or ventricular tachycardia (VT), ventricular fibrillation (VF), atrioventricular blocks (AVB), bundle branch blocks (BBB)) and the occurrence of electrical and/or mechanical complications during stay in the Coronary Care Unit (CCU) were analysed in 154 women with definte (WHO Class 1) acute myocardial infarction, admitted sequentially to the CCU over a four-year period. The prognosis in these women was then compared with the prognosis in a group which represented the general male population in the CCU and an age-matched group of men. The results showed that the long-term prognosis in women with acute myocardial infarction is remarkably similar to age-matched groups of men.

Enzyme release after myocardial infarction: comparison of serial serum alpha-hydroxybutyrate dehydrogenase with creatine phosphokinase levels

Serial measurements on serum creatine phosphokinase (CPK) and alpha-hydroxybutyrate dehydrogenase (HBD) activity were made in 17 patients with acute myocardial infarction. Activities of both enzymes were measured 4-hourly from less than 12 h after the onset of chest pain until CPK activity had returned to near-normal levels. Blood was then sampled twice daily for a further 4--6 days in order to follow the decline in HBD activity. Degradation rates (KD) were calculated for both enzymes, and individual figures for KD were used in order to estimate the total cumulative release of each enzyme. We found a significant correlation between the duration (r = 0.66, P less than 0.01) and magnitude (r = 0.67, P less than 0.01) of release of the 2 enzymes, comparing different patients with one another. Duration od HBD release was 11 h greater than the duration of CPK release in 9 of the 17 patients who were suffering from cardiac failure (t = 0.01, P less than 0.02). Degradation rate (KD) for HBD was on average about one quarter of that for CPK, but there was no significant correlation between KD for the 2 enzymes. KD did not appear to be reduced in patients with cardiac failure. We conclude that the release patterns of CPK and HBD after myocardial infarction are similar, and this strengthens the case for acceptance of total enzyme release as a valid index of myocardial infarct size.

Wenckebach phenomenon in the exit area from a transvenous pacing electrode

An unusual type of exist block from a transvenous pacing electrode was recorded in a 63-year-old man with an acute inferior infarct and cardiogenic shock. The pacemaker artefact to QRS interval increased gradually till there was loss of capture. A gradual change from I:I pacing rhythm to 4:3 and 3:2 Wenckebach cycles was recorded. This was followed by a fixed 2:I pacemaker artefact to QRS block.

Inhibition of demand pacemakers caused by potentials associated with inspiration

A 69-year-old man with a permanent demand pacemaker and a unipolar electrode system had intermittent failure of pacing during deep inspiration. Pacing was not interrupted when the unit was switched to fixed rate mode by an external magnet. Thus, the problem was not caused by a change in electrode position or to a loose connexion. The likely cause was inhibition by non-cardiac potentials, possibly myopotentials associated with respiration.

Effect of coexistent coarctation of pulmonary trunk in natural history of complete absence of pulmonary valve with ventricular septal defect

A case of complete absence of the pulmonary valve in association with a ventricular septal defect and a pulmonary artery coarctation is described. Despite these defects the patient had minimal symptoms, probably because the pulmonary artery coarctation acted as a natural banding and limited the pulmonary regurgitant flow and reduced the left-to-right shunt across the ventricular septal defect. The patient was operated on at the age of 40 and the ventricular septal defect was closed but the pulmonary artery coarctation was left alone. In view of the long-term survival in this case, it is suggested that pulmonary artery banding would reduce the symptoms and increase the life expectancy of patients with congenital absence of the pulmonary valve and a ventricular septal defect.

His bundle electrogram in patients with acute myocardial infarction complicated by atrioventricular or intraventricular conduction disturbances

Seventy-two patients with acute myocardial infarction complicated by atrioventricular or bundle-branch block or a combination of both had His bundle electrogram studies performed during their stay in the coronary care unit. In 19 of the 72 patients a repeat His bundle electrogram was performed before discharge from hospital. These studies demonstrated that 30 of the 32 patients with atrioventricular block and narrow QRS complexes had a block above the origin othe His spike (proximal block). Eleven patients in this group had repeat His bundle electrograms performed before discharge and in 3 patients there was evidence of residual atrioventricular nodal dysfunction. Both the hospital and follow-up mortality in this group was low and there was no evidence to suggest that permanent pacing would benefit these patients. Of the 18 patients with bundle-branch block and a normal PR interval, 9 had prolongation of the HV interval, but there was no difference in mortality in patients with normal or prolonged HV intervals. Twenty-two patients with bundle-branch block also developed atrioventricular block. In 5 of these patients the site of the AV block was proximal and in 14 it was distal, while 3 patients had both proximal and distal block. The hospital mortality in those patients who progressed to second- or third-degree atrioventricular block was considerably higher than in those patients who remained in first-degree atrioventricular block.

Syncope in association with Prinzmetal variant angina

A case of Prinzmetal variant angina with transient complete atrioventricular block and syncopal episodes following an anteroseptal myocardial infarction is described. The syncopal attacks were not prevented by demand cardiac pacing and were presumably caused by transient severe ischaemia of the left ventricle, with a consequent reduction in cardiac output. The left ventriculogram showed a large anterior dyskinetic area corresponding to the high grade proximal obstruction in the left anterior descending artery demonstrated by coronary angiography. All other coronary vessels appeared free of disease and it is suggested that the anginal episodes were caused by transient proximal segmental spasm of the right coronary artery. The anginal episodes were successfully prevented by a regimen of two-hourly coronary arterial vasodilator therapy.

Establishment of the Melbourne mobile intensive care service

As the majority of deaths after infarction occur in the first hour, a mobile intensive care ambulance service has been instituted in Melbourne to enable adequate care and early monitoring facilities. Initially the service was manned by doctors and ambulance officers, but currently each ambulance is manned by two specially trained officers. Over a 27-month period 52 patients have been resuscitated from ventricular fibrillation or ventricular standstill. Half of the patients had sustained a definite acute myocardial infarction and another 16 had probable but not proven myocardial infarction. Of the 52 patients, 31 survived to leave hospital and all patients known to be alive are leading active and useful lives. In spite of an initial fear that medical treatment might be overused or misused by the officers, this has not been the case, and only about 13% of patients have received drugs from the officers. This paper deals with the setting up, staffing and training of the ambulance service and reviews its results.

The floppy mitral valve syndrome--a review of fourteen patients requiring valve surgery

The correlation of clinical features with the operative findings in 14 patients with a floppy mitral valve is discussed. The clinical course is typified by rapidly progressive disability. An abrupt deterioration was present in five of our subjects and this may be due to rupture of chordae tendinea or stretching of the valve apparatus. The redundancy of the anterior cusp in 13 of our series may explain the absence of mid systolic clicks in all except one patient. The diagnosis of prolapse can be difficult to make prior to surgery because the prolapsed cusp may be masked by the regurgitant contrast medium. Hypokinesis and prominent inflow sacculation of the left ventricular inflow tract suggest an associated myocardial abnormality. Calcium was present in one valve and thus mitral valve calcification does not exclude the possibility of a floppy valve in patients with mitral regurgitation.

Verapamil induced premature ventricular beats before reversion of supraventricular tachycardia

Images