Heart disease in myasthenia gravis

Patients with myasthenia gravis (MG) may develop heart disease. Our data on 108 MG patients were examined to assess the type and frequency of this. 17 of 108 patients (16%) showed signs of heart disease which could be regarded as MG-related. 11 of these, of whom 5 died suddenly, had clinical symptoms, mainly arrhythmias. Signs of heart disease were most frequent in thymoma patients (5 of 10), and all 3 microscopically examined hearts from these patients showed a focal myocarditis. 44 spinal muscular atrophy patients serving as controls showed a 16% frequency of signs of heart disease of unknown etiology. However, only 1 of 44 spinal muscular atrophy patients (2%) had clinical symptoms as compared to 11 of 108 MG patients (10%). Together with the characteristic focal nature of the myocarditis and the microscopic similarities between lesions of heart and skeletal muscle, this indicates that the heart disease is specifically related to MG.

Long-term comparison of unipolar and bipolar pacing and sensing, using a new multiprogrammable pacemaker system

Over a six-month period a comparison was made between uni- and bipolar myocardial stimulation thresholds and R-wave sensitivity in 15 consecutive pacemaker patients. The patients received a new multiprogrammable Cordis 336 A pulse generator, that could be programmed with either uni- or bipolar circuitry. In addition, rate, output, sensitivity and pacing mode could be noninvasively programmed. The occurrence of myopotential interference at different sensitivity levels was also studied. Cordis 325-161 bipolar endocardial leads were used in all patients. In one patient, the current output sometimes had to be programmed higher bipolarly than unipolarly to capture the ventricles, otherwise no differences in threshold were found. Acutely. R-wave sensitivity was superior in 9 patients (60%) in the bipolar mode. Unipolar and bipolar electrograms were equal in 4 (26.7%), whereas unipolar R-wave sensitivity was best in only 2 (13.3%) of the patients. At a six-month follow-up, the same tendency was found. In 5 patients, bipolar sensing was superior to unipolar, while anti- and bipolar sensitivity was equal in the remaining patients. Myopotential inhibition was never seen in the bipolar mode at highest sensitivity (0.8 mV) even during provocative tests (n = 15) or 24-hour Holter monitoring (n = 12). In the unipolar mode, 14/15 patients (93.3%) showed inhibition during provocative tests and 12/12 patients (100%) during monitoring at a programmed sensitivity of 0.8 mV. No patients had myopotential interference at a sensitivity level of 3.5 mV. All patients have their pacemakers programmed in the bipolar mode after six months. This study confirms earlier acute data that the bipolar pacing mode is superior to the unipolar mode for permanent pacemaker therapy.

Bipolar atrial application of a new temporary pacing lead after cardiac operations

A new temporary pacing lead. Medtronic Model 6400, with a defined electrode surface area of 7.5 mm2, has been clinically and electrophysiologically evaluated during bipolar atrial application in 20 patients after cardiac operations. A silicon disc was used for fixation of the electrodes to the right atrium in 10 patients, and an atrial plication technique was used in the other 10. Myocardial stimulation threshold and resistance were measured throughout the postoperative period. Atrial electrograms were recorded on magnetic tape for computer analysis of amplitudes, slew rates, and signal source impedance. No significant differences (p greater than 0.1) were found in myocardial stimulation threshold between the two fixation modes. During constant-current pacing, median threshold rose from 0.65 mA to 2.3 mA. Stimulation resistance, measured during constant-voltage pacing, fell from 567 to 365 omega, with a subsequent rise to 425 omega before electrode removal. Again no difference was found between silicon disc and plication fixation of the electrodes. P-wave amplitudes were significantly higher with plication than with silicon disc fixation (2.26 versus 0.86 mV, p less than 0.01), as were slew rates (0.34 versus 0.18 V/s, p less than 0.05). Signal source impedance had a magnitude of 6 k omega. The electrodes were used successfully in 12 (60%) of the patients for diagnosis and/or treatment of arrhythmias. We find the new lead well suited for atrial application.

New temporary pacing lead for use after cardiac operations

A newly designed temporary pacemaker lead (Medtronic Model 6400), which has a solid defined electrode surface area of 7.5 mm2, was compared with a multifilamental stainless steel electrode in common use (Davis & Geck, DG). Thirty-nine patients had both types of electrodes inserted intramyocardially in the right ventricle. A DG electrode fastened to the pericardium served as a reference lead. In addition to the standard Medtronic 7.5 mm2 electrode (n = 11), specially made Medtronic electrodes with areas of 5 mm2 (n = 10), 10 mm2 (n = 10), or 7.5 mm2 with platinum-iridium tips (n = 8) were studied. Measurements of myocardial stimulation threshold and resistance were made in both electrodes throughout the postoperative period. The patients' electrograms were recorded on magnetic tape for computer analysis of amplitudes and slew rates. The Medtronic 7.5 mm2 electrodes showed overall better results than 5 and 10 mm2 leads. Maximum stimulation threshold on the Medtronic 7.5 mm2 electrodes was medium 3.4 mA versus 10 mA on DG electrodes (p less than 0.001). The tissue resistance on Medtronic 7.5 mm2 was almost double than on the Davis & Geck electrodes (median 311 ohms versus 164 ohms on the day of minimum resistance, p less than 0.001). There were no significant differences in electrogram amplitudes between the two electrode types studied (5.52 versus 4.68 mV, p greater than 0.1), but the slew rates were significantly higher on the Medtronic (0.56 versus 0.37 V/sec; p less than 0.01). The new lead is an important innovation in temporary pacemaker lead design compared to the commonly used multifilamental leads.

Electrophysiologic effects of flecainide acetate in patients with sinus nodal dysfunction

Flecainide acetate (R818) is a new antiarrhythmic agent for oral and intravenous use; it has predominantly class I properties and a long plasma half-life. Electrophysiologic effects were evaluated in 11 patients with sinus nodal dysfunction before administration of flecainide acetate and 15 to 60 minutes after intravenous administration of 1.5 mg/kg body weight of flecainide acetate given over 15 minutes. In 8 of 11 patients with maximal sinus nodal recovery time increased after flecainide acetate. However, the mean maximal sinus nodal recovery time was not statistically significantly increased from 1,929 +/- 184 (mean +/- standard error of the mean [SEM]) to 2,770 +/- 500 ms (p less than 0.10). The corrected sinus nodal recovery time increased from 875 +/- 181 before to 1,727 +/- 507 ms after administration of flecainide acetate (p less than 0.05). The sinus cycle length and sinoatrial conduction time were not significantly changed. Flecainide acetate induced a marked prolongation of the H-V interval (from 41 +/- 3 to 52 +/- 4 mg [p less than 0.01]) as well as a significant increase in the A-H interval, QRS duration, and QT100 interval. The effective and functional refractory periods of the atria increased by 12% (p less than 0.01) and 11% (p less than 0.01), respectively. The atrioventricular (AV) nodal functional refractory period increased significantly by 7% (p less than 0.01), whereas the 9% prolongation of the effective refractory period was not statistically significant. No side effects were observed. It is concluded that flecainide acetate prolongs atrial and ventricular conduction and refractoriness, and thus appears to be a potent antiarrhythmic agent. However, the sinus nodal function is depressed, and thus caution is advised in the use of flecainide acetate in patients with sinus nodal dysfunction.

Acute and chronic pulse-width thresholds in solid versus porous tip electrodes

Sixty-one patients given programmable pacemakers at initial implantation have been followed for a mean of 18 months (3-42) with non-invasive measurements of myocardial pulse-width threshold. Fifty of the patients had CPI 0505/0522 (Microlith-P/Microthin-PI) pacemakers with either Cordis 322-462 8 mm2 ball tip (n=12), Cordis 322-620 17.5 mm2 (n=23), or CPI 4116 porous tip electrodes (stimulation area 7.5 mm2 and sensing area 50 mm2) (n=15). Eleven patients had Medtronic 5985 (Spectrax-SX) pacemakers with either Medtronic 6907-R 8 mm2 ring tip (n=7), 6907 11 mm2 (n=3) or 6917 myocardial electrodes (area 12 mm2) (n=1). At acute implant, the ball tip and porous tip electrodes had the lowest stimulation thresholds, but the differences were only statistically significant in comparison with the 17.5 mm2 electrode (p less than 0.01). Chronically there were no significant differences between the various electrodes (p greater than 0.1), but the ball tip electrode tended to give best long-term results, and the porous tip electrode the poorest. Thirty-eight of the 61 patients (62.3%) had chronic pulse-width thresholds of 0.1 ms or less at approximately equal to 5 V output, indicating that pulse-width programming is a useful way to conserve battery energy. However, at some stage of the study, six of the patients (9.8%) had a pulse-width threshold of 0.5 ms or more. Pulse width should therefore not be set too narrow in standard nonprogrammable pacemakers.

Clinical and electrophysiological properties of a new temporary pacemaker lead after open-heart surgery

A new temporary pacemaker lead, Medtronic 6400, with a solid defined electrode surface area of 7.5 mm2, has been implanted in 50 patients after open-heart surgery. One electrode was inserted intramyocardially on the right ventricle, while another was placed extracardially and served as a reference lead. Forty-six of the patients were followed postoperatively with measurements of myocardial stimulation threshold and resistance. In 25 of the patients, electrograms were recorded on magnetic tape for further computer analysis of amplitudes, slew rates, and signal source impedance. During constant current pacing, myocardial stimulation threshold increased from a median of 0.4 mA one hour postoperatively to a maximum value of 2.3 mA. In two patients (4.3%) intermittent pacing failure was seen. Stimulation resistance fell from a median of 875 omega to a minimum of 487 omega, with a subsequent increase of 598 omega before electrode removal. Both mean electrogram amplitude (7.35 mV) and slew rate (0.82 V/s) had their minimum values on the sixth postoperative day. Intermittent sensing failure was observed in 2/25 patients (8%). Signal source impedance was of a magnitude not likely to contribute to sensing failure. No complications were seen from the use of this lead. The new electrode is an important improvement in temporary pacemaker lead design.

Pulse width dependent increase in the pacemaker automatic interval

From a total of 51 patients equipped with rate and pulse width adjustable pulse generators (Microlith-P 0505, Microthin-PI 0522) implanted over the last 3 years, 10 (19.6%) showed an unexpected drop in pacemaker pulse rate during pulse width programming. For one of the pulse generators used (Microthin-PI 0522), unexpected rate decrease occurred in 7/13 cases (53.8%). For all except one patient, decrease in pacemaker pulse rate corresponded with the total refractory period of the pulse generator ( 320 ms), at a certain pulse width when rate drop first occurred. In seven of the patients the pulse generator automatic interval was extended from 13 ms to 171 ms beyond the refractory period. In two patients it was necessary to replace the pulse generators. Our study strongly proves that this abnormal pacemaker functioning is a result of sensing of the polarization voltage at the pacemaker electrode/tissue interface and/or the T-wave. The polarization voltage is highly dependent on the total pacemaker electrode/tissue interface impedance. Using typical values for pulse generator output and input resistance and output capacitance, Faraday resistance, Helmholtz capacitance and tissue resistance at the electrode/tissue interface it was shown mathematically that in some cases the polarization voltage alone would be of sufficient amplitude and slew rate for pacemaker inhibition. The study demonstrates an urgent need for change in the filter characteristics by making the pulse generators less sensitive in the low frequency region and reducing the polarization voltage by reducing the output circuit capacitance.

Electrophysiological properties of a new permanent endocardial lead for uni- and bipolar pacing

Unipolar and bipolar electrode systems were compared for electrogram amplitudes and slew rates, signal source impedance, and myocardial stimulation threshold and resistance in 15 consecutive patients who received a new endocardial electrode (Cordis 325-161). The bipolar electrograms showed the highest amplitude in nine of the patients (60%). The unipolar and bipolar electrograms were equal in four patients (26.7%), whereas the unipolar electrograms were highest in only two patients (13.3%). The difference in mean amplitude between bipolar (11.1 mV) and unipolar (10.1 mV) electrograms was statistically significant (p 0.05). Mean slew rates were almost equal (1.7 versus 1.6 V/s; p greater than 0.1). The bipolar electrode system always gave somewhat higher signal source impedance than the unipolar system (p 0.001). The current threshold was significantly lower during bipolar pacing (0.59 mA) in constant current pacing mode, than during unipolar pacing (0.65 mA) (p less than 0.05). No significant differences were found during constant voltage pacing. Stimulation resistance was highest in the bipolar electrode system (p less than 0.001). We conclude that the bipolar electrode system is as good as, or better than, the unipolar system both for ventricular sensing and for pacing.

Antihypertensive therapy in patients above age 60 with systolic hypertension. A progress report of the European Working Party on High Blood Pressure in the Elderly (EWPHE)

1. Although systolic blood pressure elevation is responsible for increased incidence of cardiovascular accidents in old people, the preventive benefit of lowering systolic hypertension in elderly has not been confirmed. 2. A double blind study comparing the effects of a placebo and of an active regimen (hydrochlorothiazide-triamterene with or without methyldopa) in people over 60 years with isolated systolic hypertension has been undertaken by the European Working Party on High blood pressure in the Elderly (EWPHE). 3. The actively treated group shows a lowered sitting blood pressure (-15/6 mm Hg), a mild increase of serum creatine, serum uric acid and blood glucose and a mild decrease of serum potassium after two years of treatment when compared to the spontaneous changes observed in the placebo treated group. 4. The study is continuing to evaluate if the blood pressure reduction prevents or reduces the incidence of cardiovascular accidents, although some biochemical changes were provoked by the treatment.

Spontaneous heart activity in pacemaker treated patients with high-grade atrioventricular block. A Holter monitor study

A Holter monitor study was performed to assess the occurrence of spontaneous heart activity in 70 pacemaker treated patients (mean age 72.1 years) with high-grade atrioventricular (AV) block, who have been treated with permanent pacemakers for a mean of 60 months (range 5-161). Nineteen patients had asynchronous (VOO), and 51 QRS-inhibited (VVI) pacemakers. The patients were monitored for a mean of 23 hours (range 15.5-26). Twenty-five patients were re-studied for day-by-day variations in spontaneous heart activity. At clinical observation, thirty-eight patients had some kind of spontaneous cardiac activity, mostly ventricular ectopic beats. Three patients had short episodes of sinus rhythm of more than 70 beats/min. Patients in functional class III-IV (NYHA) or with an enlarged heart had the most spontaneous heart activity. No tachyarrhythmias precipitated by interference between intrinsic heart beats and asynchronous pacemakers were seen. Twenty patients studied twice had a relatively stable occurrence of spontaneous heart activity, while five (20%) varied considerably. On the basis of these long-term observations it is difficult to predict when interference rhythm will occur, and asynchronous pacemakers therefore cannot be recommended for the first implantation.

Myopotential inhibition of unipolar QRS-inhibited (VVI) pacemakers, assessed by ambulatory Holter monitoring of the electrocardiogram

Seventy-four patients with unipolar QRS-inhibited pacemakers (VVI) were Holter monitored to assess the occurrence of pacemaker inhibition caused by skeletal muscle potentials during daily activities. Fifty patients had high-grade atrioventricular block and 24 had sinoatrial disease. Chest wall stimulation prior to monitoring revealed asystole of > 4 seconds duration in 22 patients, and ventricular rates between 25 and 56 beats per minute in 52 patients. Fifty-one patients (69%) had one or more episodes of pacemaker inhibition from myopotentials. Inhibition occurred in all types of pacemakers studies, but was most frequent and of longest duration in patients with Siemens-Elema 207/70 (13/14 patients), Cordis Omni-Stanicor (6/7 patients), CPI Microlith (5/6 patients), and Medtronic 5945 (8/10 patients). This was not unexpected considering the filter characteristics of the pacemakers. Nine patients (12%) presented symptoms which might be ascribed to pacemaker inhibition. The longest asystole observed was 3.2 s. Seven patients had pacemakers spikes falling on or near T-waves of spontaneous heart beats because their pacemakers had been rendered refractory by myopotentials. No serious arrhythmias were seen during episodes of pacemaker inhibition or interference. More emphasis should be put on the improvement of filter characteristics of unipolar VVI-pacemakers. Pacemaker patients with symptoms of myopotential inhibition should be equipped with either a bipolar or ventricular triggered (VVT) pacemaker or with a sensitivity and/or pacing mode programmable pacemaker.

Inhibition/filter characteristics and input impedances of QRS-inhibited demand pacemakers determined by in vitro studies

There is still no standardized test procedure established for demand pacemakers. Much work has been done to reduce demand failures, but more knowledge is needed to arrive at better results. This study was initiated by in vivo observations of pacemaker malfunctions and unwanted pacemaker effects, the objective being to arrive at a better match between spontaneous cardiac activity and the pacemaker system. The study describes inhibition characteristics and input impedances in some modern temporary as well as permanent QRS-inhibited pulse generators, based on in vitro experiments with various signal waveforms. The different pulse generators tested showed a wide variety of inhibition characteristics. The interrelationship between signal amplitude and maximum derivative required to obtain pacemaker inhibition is pointed out. A better approach to describe the inhibition characteristics of demand pacemakers seems to be the introduction of the time integral (voltseconds) instead of the maximum derivative of a signal (Fig. 3). It is shown that this method nearly removed the discrepancies in inhibition characteristics between different pulse waveforms used. The input impedances were also widely dispersed and were in some instances of a magnitude so low that it would lead to marked reduction of the electrogram amplitude in case the electrode/tissue interface impedance was high. The characteristics of temporary pulse generators were in several respects different from those of the permanent ones. The results obtained with a temporary unit during a test procedure are therefore not the same as for a permanent pacemaker system.

Temporary pacemaker treatment in open heart surgery: pre- to postoperative changes in the electrogram characteristics

Thirty-three patients undergoing cardiac surgery in general hypothermia were investigated during temporary pacemaker treatment for changes in right ventricular electrogram amplitudes (AMAX, UMAX) and maximum derivatives (DMAX, SMAX) from pre-to postoperative phase (AMAX = amplitude of the part of the electrogram with highest mean maximum derivative (SMAX), DMAX = maximum derivative, UMAX = maximum amplitude deflection). Standard commercially available electrodes were used in 28 of the patients. A paired comparison (n = 29) showed a fall in AMAX from 8.64 +/- 0.91 mV (mean +/- SEM) preoperatively to 4.94 +/- 0.43 mV (p < 0.001) between the 4th and 6th postoperative day; UMAX dropped from 11.09 +/- 0.95 mV preoperatively to 5.44 +/- 0.42 mV (p < 0.000001) from the fourth to the sixth postoperative day. In the same period DMAX fell from 1.57 +/- 0.13 V/s to 0.67 +/- 0.05 V/s (p < 0.000001), and SMAX from 0.76 +/- 0.06 V/s to 0.32 +/- 0.02 V/s (p < 0.000001). The most marked fall in amplitudes and maximum derivatives occurred during the first 24 hours. A slight, but nonsignificant increase occurred in amplitudes and maximum derivatives from the 4th to 6th postoperative day until the electrodes were removed the 10th to 19th postoperative day. Amplitudes and maximum derivatives were of the same value in patients with aortic valve compared with coronary heart diseases in spite of a more deteriorated myocardial function in the former group. The changes in amplitudes and maximum derivatives followed the same pattern in the two groups from the pre- to postoperative phase. This indicates that the additional local hyperthermia applied to the patients undergoing valve surgery was of no importance in the electrogram changes. Despite the fact that the electrogram maximum derivative and maximum amplitude needed to inhibit a temporary pulse generator are of a low magnitude, the values found were so small that they might provoke demand failure. This actually occurred in four patients.

Demand failures occurring during permanent pacing in patients with serious heart disease

Demand failures during permanent cardiac pacing were studied in four patients with coronary heart disease and cardiomyopathies, by means of in vivo and in vitro analyses of the pacemaker system. A common feature of the electrogram analyses (except during a second replacement in one patient), was extremely low values of amplitudes (0.77-4.36 mV) and maximum derivatives (0.16-1.06 V/sec). In spite of low electrogram amplitudes, the myocardial threshold values were low in all patients. An attempt in one patient at unipolarizing a bipolar system made the adaptation between electrogram and pulse generator more difficult. Autopsy showed that the tip of the bipolar electrode was positioned in a fibrotic area of the myocardium. The signal available for the sensing circuit will also be reduced because of voltage division between the electrode/tissue interface impedance and the input impedance of the pulse generator. Although the pulse generators used had a high input impedance (10-50 K omega), the tissue interface impedance may have caused a further reduction in the electrogram amplitude of 10-30%. This may have contributed to demand failure. In vitro studies confirmed that test pulses with characteristics similar to those of the electrograms found in this investigation, were inadequate for pacemaker inhibition. Special care should be taken during electrogram recordings in patients with severe myocardial disease. One should consider the implantation of a high sensitivity pulse generator or the recently introduced sensitivity programmable pulse generators as first choice for this group of patients.

The interdependence between electrogram, total electrode impedance and pacemaker input impedance necessary to obtain adequate functioning of demand pacemakers

Electrogram maximum derivatives (DMAX, SMAX) and electrogram amplitudes (AMAX, UMAX) (Figure 2), were studied in 71 cases during permanent pacemaker treatment. During the acute phase, (at first implantation), 29 patients were studied, and during the chronic phase, (at pulse generator replacement), 42 patients were studied. Of these patients, 27 (acute phase) and 36 (chronic phase) were studied for tissue impedance (RT) and interface impedance (Faraday resistance RF and Helmholtz capacity CH). DMAX and SMAX changed from 3.47 +/- 0.33 V/s (mean +/- SEM) to 2.46 +/- 0.23 V/s and 1.93 +/- 0.20 V/s to 1.32 +/- 0.12 V/s; p < 0.02; p < 0.01. AMAX and UMAX remained nearly unchanged from acute to chronic phase. A paired comparison in 13 patients showed almost identical results. Electrograms recorded in patients with bundle branch block showed no statistical difference in DMAX, SMAX, AMAX, and UMAX compared with electrograms recorded in patients with QRS-complexes of normal duration. No correlation was found between rise in myocardial threshold and fall in DMAX and SMAX from acute to chronic phase; p > 0.8, p > 0.5. Patients with coronary heart disease were found to have significantly higher AMAX than patients classified as having rhythm disturbances of primary cause; p < 0.01. Extremely low values of amplitudes and maximum derivatives were found in some patients with myocardial infarctions and cardiomyopathies. No difference existed in DMAX, SMAX, AMAX, and UMAX recorded from electrodes with a 8 mm2 area compared with a 12 mm2 area (p > 0.5). RT was statistically significantly higher on the smaller compared with the larger surface electrodes (p > 0.005). There was a slight but not statistically significant fall in RT from acute to chronic phase (p > 0.2). RF ranged from 2.0-94.6 kohms. There was no statistically significant differences between the 8 mm2 compared with the 12 mm2 electrodes (p > 0.2). CH varied between 0.7 and 37.0 microfarads, with significantly lower values for the smallest electrodes (p < 0.05). In patients with electrograms of borderline amplitudes and maximum derivatives for being sensed, the low CH found with the small tip electrodes, will gave a higher risk of demand failure if the input impedance in the sensing circuit of a demand pacemaker is too low.

Temporary pacemaker treatment in open heart surgery: variation in myocardial threshold, tissue and interface impedances in man

Myocardial threshold and impedance of adequately insulated multicore metal electrodes (lengths l1 and l2) were investigated in 28 patients undergoing open heart surgery. Increase in current threshold from the pre-to postoperative period was: 607 +/- 102% (mean +/- SEM) with a constant-current pulse generator and 885 +/- 129% with a constant-voltage pulse generator. Tissue impedance (RT - initial impendance) calculated as voltage/current ratio 90 mus into the pulse changed from 564 +/- 34 omega before surgery to a minimum of 134 +/- 7 omega. Thereafter, there was a gradual increase in RT to 162 +/- 9 omega the day of electrode removal. In 25 of 28 patients the minimum values were reached the third to eighth postoperative day. Electrode/tissue interface impedances--Faraday resistance (RF) and Helmholtz capacity (CH)--were calculated from regression analysis of loaded and unloaded electrograms using the method of least squares. The RF showed a fall from 14.7 +/- 1.4 K omega to 5.2 +/- 0.3 K omega, and the CH (20-40 Hz) rose from 6.0 +/- 0.9 mu F to 15.5 +/- 0.8 muF preoperatively to the day of minimum tissue impedance. There were no further changes until the day of electrode removal. A significant positive correlation was found between CH (p < 0.002), current threshold (p < 0.005) and equivalent electrode length [lequ = l1 X l2/(l1 + l2)]. The electrode signal source impedance calculated from RT, RF and CH was of a magnitude not likely to contribute to demand failures. The low postoperative electrode impendance resulted in excessive load on the constant-voltage generator (condenser discharge type), rendering stimulation of the heart with reasonable current values impossible.

Haemodynamic long-term effects of metoprolol at rest and during exercise in essential hypertension

1 Twelve men with untreated essential hypertension in WHO stage I were studied on an outpatient basis to evaluate the haemodynamic long-term effect of a new beta-adrenoceptor blocker, metoprolol. 2 Oxygen consumption, heart rate, cardiac output (Cardiogreen) and intraarterial brachial pressure were recorded at rest in a supine and sitting position and during steady state work at 300, 600 and 900 kpm/min. 3 The subjects were treated with metoprolol (dose 50-250 mg/day) as the sole drug for 1 year and the haemodynamic study was repeated. 4 Mean arterial blood pressure was reduced about 12% at rest and 9% during exercise. The heart rate was decreased about 22% at rest and 20% during exercise. There was no significant compensatory increase in the stroke volume and consequently the cardiac index was reduced about 22% at rest sitting and about 17% during exercise. There was no decrease in total peripheral resistance. 5 No side-effects were seen. 6 The major haemodynamic long-term effects of metoprolol in mild and moderate essential hypertension resemble those seen by other beta-adrenoceptor blockers like alprenolol, atenolol and timolol. The study has not given support to the assumption that metoprolol should cause less depression in cardiac output than other beta-adrenoceptor blockers.