Clinical evaluation of a thin bipolar pacing lead

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined, polyurethane, with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm2 cathode tip is coated with polyethylene glycol, a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432-04 and 24 ventricular model 430-10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42, and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 +/- 0.05 ms in the atrium and 0.10 +/- 0.02 ms in the ventricle, pacing impedances 443 +/- 104 omega and 520 +/- 241 omega, while median electrogram amplitudes were > or = 3.5 mV and > or = 7 mV, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration--the findings are explainable by the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.

New temporary atrial and ventricular pacing leads for patients after cardiac operations

We have studied two new temporary pacing leads (Medtronic 6491 and 6492) intended for pacing after cardiac operations. The conductor has stainless steel strands coated with polyethylene connected to a 4' mm2 surface area, stainless steel, smooth, tapered electrode. A soft 4-0 coiled polypropylene fiber served as as fixation mechanism in the heart. The study included 15 children (aged 3 months to 7 years, body weight 4.4 to 20 kg) with a variety of congenital heart defects and 15 adults (aged 45 to 78 years) with coronary artery disease (n = 13) and aortic valve disease (n = 2). A pair of leads each was placed in a bipolar fashion in the right atrial wall and nonsystemic ventricle in the children (median implant duration 12 days) and in the right atrial wall only in the adults (median implant duration 9 days). The atrial current threshold values in children increased from 0.61 +/- 0.34 mA immediately after implant to 2.08 +/- 1.86 mA at explant (p < 0.002). In the adults the threshold values increased from 0.95 +/- 1.44 mA immediately after implant to 2.76 +/- 2.76 mA at explant (p < 0.002). In the ventricle the threshold values increased from 0.38 +/- 0.13 mA immediately after implant to 2.22 +/- 1.63 mA at explant (p < 0.002). Tissue resistance immediately after implant measured 809 +/- 182 omega at explant (children, p = not significant). Corresponding values in adults were 778 +/- 190 omega and 599 +/- 91 omega (p < 0.004). In the ventricle resistances changed from 1019 +/- 143 omega to 876 +/- 137 omega (p < 0.05). P wave amplitudes measured 1.8 +/- 1.5 mV immediately after implant and decreased to 1.6 +/- 1.2 mV at explant (p = not significant, children) and 2.0 +/- 1.3 mV to 1.8 mV (p = not significant, adults). R wave amplitude were 13.1 +/- 3.0 mV immediately after implant and fell to 8.7 +/- 4.5 mV at explant (p < 0.005). Thus, threshold values, tissue resistances, and electrogram and pliable amplitudes assured a safe pacemaker function. The small diameter and pliable texture of these leads provided a smooth surgical handling. They were found particularly suitable in children.

Clinical study of a new activity sensor for rate adaptive pacing controlled by electrical signals generated by the kinetic energy of a moving magnetic ball

A new rate adaptive pacemaker (Sensorithm) controlled by an activity sensor providing electrical signals induced by a magnetic ball moving freely in an elliptical cavity surrounded by two copper coils, was implanted in ten patients; mean age of 75 years (range 64-89). Six patients had atrioventricular block and four had sinus node disease. In auto-set testing procedure during a 1-minute walk in the corridor, a slope resulting in a maximum rate of 95 beats/min was selected in every patient, and a medium reaction time was programmed. During graded treadmill exercise tests the heart rate increased 63 +/- 7 beats/min to 135 +/- 6 beats/min in rate adaptive pacing mode (VVIR), and 15 +/- 6 beats/min (P < 0.0001) in ventricular pacing mode (VVI). The symptom-limited exercise time was 9.1 +/- 1.1 minutes and 8.2 +/- 1.2 minutes (P = NS), and the exercise distance was 501 +/- 95 meters and 428 +/- 92 meters (P < 0.05) in VVIR and VVI pacing mode, respectively. The maximum oxygen uptake was 20.6 +/- 2.6 mL/kg per minute in VVIR pacing and 18.1 +/- 2.1 mL/kg per minute (P < 0.05) in VVI pacing. The delay time until the pacing rate increased 10% of the total rate increase at onset of treadmill exercise was 4.4 +/- 0.7 seconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term clinical performance of a central venous oxygen saturation sensor for rate adaptive cardiac pacing

Rate adaptive ventricular pacemakers using central venous oxygen saturation (O2Sat) to control the pacing rate have been implanted in 14 patients (mean age 71 years), with a mean follow-up period of 44 months (range 2-63 months). In eight patients the pacemakers were replaced due to signs of battery depletion after an implant duration of 39-58 months. During bicycle exercise testing the O2Sat decreased on average from 61% +/- 4% at rest to 36% +/- 4% (P < 0.0001) at peak exercise, and the maximum pacing rate was 122 +/- 5 beats/min. The time delay until the O2Sat had dropped 10%, 65%, and 90% of the total reduction during exercise was 4.8 +/- 0.9 seconds, 39.8 +/- 3.8 seconds, and 71.3 +/- 7.5 seconds, respectively. The O2Sat decreased 9.4% +/- 2% (P < 0.005) from resting supine to resting sitting. Oxygen breathing increased the telemetered O2Sat from the pacemaker by 8.4% +/- 1% (P < 0.001). During follow-up the O2Sats were relatively stable in 50% of the patients, but demonstrated significant fluctuations in the others. At 1-year invasive follow-up O2Sat measured by the pacemaker decreased 22% +/- 2%, and in blood samples from the right ventricle 22% +/- 2% from rest to 3 minutes exercise at 25 watts. There was a significant correlation between O2Sat measured by the pacemaker and in blood samples from right ventricle (n = 105; r = 0.73; P < 0.001). In two patients the O2Sat dropped significantly during pneumonia. In another patient episodes of angina pectoris was associated with low O2Sat and a concomitant fast pacing rate.

The acute effects of induced tachycardia on coronary sinus and arterial plasma levels of atrial natriuretic peptide and on arterial catecholamines

Atrial natriuretic peptide (ANP) was measured in coronary sinus (CS) plasma in seven patients with induced tachycardia. Right atrial pressure (RAP) and femoral artery (FA) levels of ANP, noradrenaline (NA) and adrenaline (A) were measured before and after 5 min with tachycardia. During tachycardia, ANP in CS plasma increased from 381 +/- 273 (mean +/- SD) to 1376 +/- 1191 pmol l-1 (p < 0.0001), and ANP levels in FA plasma from 89 +/- 48 to 231 +/- 151 pmol l-1 (p < 0.005). A significant increase was observed for peak RAP, whereas mean RAP remained unaltered. While no correlation existed between the increase in CS plasma ANP level and RAP, significant correlations were found between the changes in FA plasma ANP and RAP, and between FA plasma levels of ANP and NA. Following tachycardia, significant correlations were found both between ANP in CS and FA plasma and between the changes in these plasma levels. Whereas the changes in FA plasma levels of ANP during tachycardia seems dependent of RAP and arterial plasma levels of NA, the CS plasma ANP level appears to be independent of the two factors, probably because CS plasma ANP are drained mainly from the left side of the heart.

Preliminary experience with nonthoracotomy implantable cardioverter defibrillators in young patients. The Medtronic Transvene Investigators

Implantable cardioverter defibrillators represent an important treatment option for patients with life-threatening tachyarrhythmias. However, the requirement for surgical access to the thorax contributes to significant procedural morbidity with ICD implantation. This study was performed to assess an initial experience with a nonthoracotomy approach to ICD lead implantation in young patients. An international survey identified 17 patients, ranging in age from 12-20 years (mean = 16.7 +/- 2.4) and weighing from 33-89 kg (mean = 60.6 +/- 13.3), who had undergone placement of the Medtronic Transvene defibrillator lead system. Implant indications were aborted sudden cardiac death in 15 patients and recurrent ventricular tachycardia or familial sudden death in 2 patients. At a median follow-up of 7.9 months, 9 of 17 patients had received at least one ICD therapy. There have been no deaths. Complications included patch or generator erosion (3 patients), lead dislodgement (1 patient), and ICD system infection requiring explanation (1 patient). The initial experience with nonthoracotomy ICDs in young patients appears promising. This approach may be particularly advantageous for patients who have undergone prior thoracotomy. Prospective clinical trials will be required to establish the applicability of these lead systems to select patient populations.

[Treatment of ventricular tachyarrhythmias with an implantable pacemaker-cardioverter-defibrillator]

During the period from November 1989 to January 1992, 17 patients with ventricular tachyarrhythmias received an implantable pacemaker-cardioverter-defibrillator. The material consists of three female and 14 male patients with an age range of 13-66 years, mean 50.8 +/- 16.6 years. 13 patients had coronary artery disease, one cardiomyopathy, one a myocarditis sequela and two primary rhythm disorder. Four patients received epicardial and 13 endocardial electrode systems. The observation period varied from 4-30 months (april 1992), mean 15.2 +/- 8.8 months. 11 out of 17 patients (65%) experienced one or more episodes of tachyarrhythmias which was treated successfully with overdrive pacing (ramp or burst), cardioversion or defibrillation. One patient died of heart failure after an observation period of 13 months. His pacemaker-cardioverter-defibrillator had been activated more than 100 times. Two children, 13 and 15 years, were treated successfully for ventricular fibrillation four and five months after implantation of the device. The actual one year survival is 100%. Assuming that therapy with a device had not taken place, and that the six patients who experienced episodes of ventricular fibrillation died, the hypothetical probability of survival would have been 62.1 +/- 12.3%.

Efficacy of automatic multimodal device therapy for ventricular tachyarrhythmias as delivered by a new implantable pacing cardioverter-defibrillator. Results of a European multicenter study of 102 implants

BACKGROUND

Third-generation implantable cardioverter-defibrillators are devices designed to treat ventricular tachycardia (VT) and ventricular fibrillation (VF) by means of overdrive pacing, cardioversion, or defibrillation. So far, the efficacy of tiered therapy has been documented only in small series. Therefore, a European multicenter clinical evaluation study of a new tachyarrhythmia control device, the Medtronic PCD pacer-cardioverter-defibrillator with epicardial patch-lead configuration, was undertaken.

METHODS AND RESULTS

We report on 102 patients (mean age, 55 +/- 13 years) from 11 European centers. PCD devices implanted between May 1989 and February 1991 were included. The patients suffered from hemodynamically significant ventricular tachyarrhythmias not suppressed by antiarrhythmic drug therapy and unrelated to acute myocardial infarction; one patient had nonsustained VT and severely depressed left ventricular function. Seventy patients had coronary artery disease with old myocardial infarctions, 23 had cardiomyopathies of various etiologies, and nine patients had no detectable heart disease. Mean ejection fraction was 36 +/- 14% (range, 10-76%). Mean intraoperative defibrillation threshold (51 patients) was 10.6 +/- 5.1 J (range, 2-18 J). The documented follow-up ranged from 1 to 21 months (mean, 9.4 +/- 5.8 months), or 79.9 cumulative patient-years. Perioperative mortality was 3.9%. The actuarial survival rate at 12 months was 91%. One sudden arrhythmic death occurred. Sixty patients (58%) received device therapy. Seventeen patients had therapies only for "VF" episodes, 16 patients only for VT, and 28 patients for VT and "VF" episodes. Based on device memory data, 1,235 spontaneous VT episodes were detected and treated in 43 patients. Twelve hundred four of these VT episodes received painless initial antitachycardia pacing therapy, restoring sinus rhythm in 91%. The 108 ongoing episodes received 209 multiple therapeutic attempts. Eighty-five additional overdrive pacing therapies restored sinus rhythm in 30%. Initial ineffective antitachycardia pacing therapies received 51 cardioversion pulses. The success rate was 61%. Seventy-three additional cardioversion pulses were delivered to backup ineffective pacing therapy as well as ineffective secondary cardioversion pulses. Their success rate was only 40%. Two hundred eighty-six spontaneous episodes were detected in 44 patients as "VF." Overall defibrillation efficacy was 97.6%.

CONCLUSIONS

The implanted device nearly eliminates sudden arrhythmic death in patients with documented, potentially fatal ventricular tachyarrhythmias. Automatic tiered therapy is highly effective to restore sinus rhythm, provided that an integrated two-zone tachycardia detection algorithm is used, assigning lower tachycardia rates to overdrive pacing and/or cardioversion and higher tachycardia rates to defibrillation. In general, spontaneous VTs can be terminated by automatic overdrive pacing, and painful or disturbing countershock therapies are not required to terminate the majority of spontaneous VT episodes.

[Sudden cardiac death]

Sudden cardiac death is instant unexpected death that occurs within one hour of an abrupt change in a person's stable clinical state. The mechanism is generally a ventricular tachyarrhythmia. The underlying pathology is usually coronary heart disease. In 1990, 18 patients who survived sudden cardiac death, excluding those with acute myocardial infarction, were evaluated and treated in our institution. 15 patients had coronary heart disease, one had hypertrophic cardiomyopathy, one had dilated cardiomyopathy and one had a replaced aortic valve. Evaluation included heart catheterization and electrophysiological examination. Treatment was specifically tailored to each patient according to etiology, results of all tests and the patient's prognostic factors. Treatment included a permanent pacemaker-cardioverter-defibrillator, antiarrhythmic drug therapy, aortocoronary bypass and betablocker therapy.

[Intermittent bradyarrhythmia in infants and small children treated with permanent pacemaker]

Four children aged two, two and four months and five years respectively, with intermittent cardiac bradyarrhythmias and otherwise normal hearts are described. The diagnoses were based upon findings by telemetry and 24-hour ECG-recordings. Two patients had sinus node disease, one patient had intermittent complete atrioventricular block, and the fourth had a permanent first degree atrioventricular block and intermittent high grade second degree atrioventricular block. All patients presented serious symptoms with apparent life-threatening events before admission. They were given a permanent cardiac pacemaker. One patient experienced recurrent excessive increase in the myocardial stimulation threshold, leading to further syncopal episodes. All patients are developing adequately with normally functioning pacemakers.

The influence of supine relaxation on blood pressure, heart rate and atrial natriuretic peptide in normal subjects

The effect of recumbent rest on plasma atrial natriuretic peptide (ANP) concentration, mean blood pressure (MBP) and heart rate was studied in 26 normal human volunteers. Plasma ANP concentration, MBP and heart rate were determined after 10 min sitting and after 2, 5, 8, 15 and 30 min of recumbency. During the first 5 min of recumbency there were significant decreases in both MBP (p less than 0.001) and heart rate (p less than 0.001) compared with sitting. There was a small but significant fall in plasma ANP concentration (p = 0.02) after 30 min of recumbency compared with sitting. No further reduction in MBP or heart rate occurred after 5 min supine. The level of MBP following 5 min supine correlated significantly (r = 0.44; p = 0.02) with the plasma ANP concentration 25 min later. Blood pressure and heart rate are highly dependent on posture and relaxation, and plasma ANP concentration in lesser degree. It is necessary to wait for stable baseline values to develop before any comparisons between blood pressure and plasma ANP are done. If it is assumed that a causative relation exists between blood pressure and plasma ANP level, it appears there may be a delay of 20-30 min between a change in blood pressure and the physiological response of plasma ANP level. This observation may have implications for the interpretation of the relation between blood pressure and plasma ANP concentration in healthy individuals.

Electrophysiologic and clinical effects of flecainide for recurrent paroxysmal supraventricular tachycardia

The antiarrhythmic effects of flecainide acetate were evaluated in 9 patients with paroxysmal atrioventricular (AV) nodal tachycardia and 17 patients with AV tachycardia. An electrophysiologic study was performed before and after intravenous flecainide acetate, 2 mg/kg body weight, was infused over 15 minutes and was followed by a maintenance infusion of 1.6 mg/kg given over 1 hour to 26 patients and during oral treatment to 15. Treatment with oral flecainide acetate was continued for 14 +/- 5 months. Intravenous flecainide acetate terminated AV nodal tachycardia by blocking the retrograde fast pathway conduction in 7 of 7 patients and AV tachycardia by blocking retrograde conduction in the extranodal pathway in 10 of 10 patients. AV nodal tachycardia and AV tachycardia were noninducible in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. Long-term treatment with oral flecainide acetate suppressed AV nodal tachycardia and AV tachycardia in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. A favorable outcome was associated with block in the accessory pathway after intravenous flecainide acetate and noninducibility during oral treatment. Recurrences preferentially occurred in the younger patients. Flecainide acetate is effective in the acute and long-term management of paroxysmal supraventricular reentry tachycardia by suppressing conduction through the retrograde fast limb of the tachycardia circuit. The clinical effect can be predicted by electrophysiologic testing.

Combined intoxication with digitoxin and verapamil. The possible inhibition of sensitisation to digitalis-specific antiserum by toxic drug concentrations

The clinical course in a patient with a combined intoxication with digitoxin (maximal serum level 357 nmol/l) and verapamil is described. The patient received two injections of digitalis-specific antiserum. No adverse reactions to the therapy was seen, and the antiserum markedly shortened the plasma half-life of digitoxin. In vitro studies indicate that digitoxin in concentrations seen during the intoxication may have an immunosuppressive effect, thereby reducing the risk of sensitisation to the antiserum.

Assessment of the work capacity and relationship between rate response and exercise tolerance associated with activity-sensing rate-responsive ventricular pacing

The relationship between rate response and exercise tolerance was studied by measuring the symptom-limited maximum treadmill time (MTT)both during fixed rate VVI pacing and during VVI + activity mode pacing (RRP) in 15 patients (mean age, 73 years) who had received rate-responsive ventricular pacemakers. Their indications were atrioventricular block, sino-atrial block, and atrial fibrillation with slow ventricular response. Basic rate was programmed to 60 ppm in both pacing modes; rate response and activity threshold were programmed to 5 and medium, respectively. The order in which the two pacing modes were tested was randomly determined. The MTT was, on average, 29% longer in RRP than in VVI mode with a mean of 12 minutes in VVI and 14.8 minutes in RRP (p less than 0.001). For the subgroup of eight patients with paced-only rhythm the average increase in MTT was 38% with a mean of 9.5 minutes in VVI and 12.8 minutes in RRP (p less than 0.01). Seven patients who showed episodes of spontaneous rhythm, increased their average MTT by 17% (mean in VVI, 14.9 minutes; in RRP, 17.1 minutes; p less than 0.02). During RRP, a significant positive correlation existed between MTT and the increase in heart rate (N = 15; r = 0.83; p less than 0.001). In 12 patients with paced-only rhythm, the pacing rate remained at the programmed basic rate when the patients were lying, sitting, and standing and increased to 86 +/- 4 ppm during casual walking, and to 101 +/- 4 ppm during jumping up and down with the pacemaker programmed to the above-mentioned parameters. The maximum pacing rate during jumping corresponded with the maximum pacing rates measured from Holter recordings during normal daily activities.

Noninvasive assessment by Doppler and M-mode echocardiography of hemodynamic responses to temporary pacing and to ventriculoatrial conduction

A new, dual-chamber temporary pacing lead was introduced via the subclavian vein in 20 patients who needed a temporary pacemaker. Stroke volume (SV) was measured continuously by combining M-mode and noninvasive Doppler echocardiography during spontaneous rhythm (SR), AV sequential pacing at a positive AV interval (DP), ventricular pacing (VP) and AV sequential pacing at a negative AV interval (VA pacing). The valvular functions were determined by Doppler echocardiography. Left ventricular dimensions and function, and left atrial size were measured by M-mode echocardiography. In the nine patients with no valvular heart disease and with no ventriculoatrial (VA) conduction (group I) the CO increased 83 +/- 11% during DP and 42 +/- 9% during VP as compared to during SR when the heart rate (HR) was increased from 34 +/- 3 to 72 +/- 1 beats/min. The CO was 29 +/- 3% higher during DP than that during VP. In the seven patients with valvular heart disease and with no VA conduction (group II), the increment in CO compared to that during SR was 53 +/- 12% during DP and 31 +/- 11% during VP; the CO was 17 +/- 4% higher during DP than that during VP. In the four patients with spontaneous VA conduction (group III), the CO during DP was 35 +/- 10% greater than that during VP, which did not result in an increase in the CO compared to that during SR in spite of an increase in HR from 52 +/- 8 to 74 +/- 2 beats/min. The study demonstrated that DP is the preferred temporary pacing mode and also that VA conduction during VP resulted in a mean decrease of 20% in CO compared to that during VP without VA conduction. The hemodynamic benefit from DP compared to SR seems to decrease when the left ventricular end-diastolic dimension increases. Furthermore, patients with large left ventricular end-systolic dimensions seem to have a lower increase in stroke index during DP as compared to that during VP than patients with smaller end-systolic dimensions.

A time-related study by Doppler and M-mode echocardiography of hemodynamics, heart size, and AV valvular function during activity-sensing rate-responsive ventricular pacing

Noninvasive Doppler and M-mode echocardiography were used to: measure stroke volume (SV), left atrial (LA) size, left ventricular end-diastolic (EDD), end-systolic dimensions (ESD), left ventricular fractional shortening (FS), and for determination of mitral and tricuspid insufficiency (MI and TI) before starting and after 1, 3, and 6 months of rate-responsive ventricular pacing (RRP). The study group consisted of 13 patients (mean age, 75 years) who could be expected to benefit from an increase in cardiac output mediated by an increment of heart rate during exercise. In VVI + activity mode (RRP), the pacemaker was programmed to a basic heart rate of 60 and a maximum heart rate of 125 bpm. The SV at rest was 71 +/- 5 before RRP, and fell to 57 +/- 4 after 3 months (p less than 0.05) and to 53 +/- 4 ml/beat after 6 months of RRP (p less than .01). The LA size and ESD were unchanged during follow-up. The EDD decreased from 6.2 +/- 0.3 to 5.4 +/- 0.2 (p less than 0.002) during the first 6 months of RRP. The FS was reduced from 33 +/- 4 to 27 +/- 3% (p less than 0.02) during the first 6 months of RRP. Four of 6 patients treated previously with a VVI pacemaker (mean duration, 9 years) had MI + TI, and 3 of the 7 patients not paced previously had MI before RRP. In the last group, 1 new patient developed MI, 1 new patient developed MI + TI, and 2 patients who had MI also developed TI within 6 months of pacing. Thus, of 13 patients, 9 (69%) had either MI or MI + TI.

Ventricular tachyarrhythmia initiation in a canine model of recent myocardial infarction. Comparison of unipolar cathodal, anodal and bipolar stimulation

Ventricular tachyarrhythmia initiation was compared using unipolar cathodal, anodal and bipolar programmed stimulation at 21 sites in 5 normal adult mongrel dogs and 67 noninfarct sites in 16 dogs 3-5 days after experimental myocardial infarction. For this purpose, the minimum number of extrastimuli required for tachyarrhythmia initiation was determined in each pacing mode using twice cathodal threshold current for the drive beats and all extrastimuli except the last. The current and pacing mode were varied for the last extrastimulus (S2, S3 or S4). In the 5 normal dogs, ventricular fibrillation was reproducibly inducible from only 1/21 sites, and only in the cathodal mode. In 15/16 (94%) of the myocardial infarction dogs, a sustained ventricular tachycardia or ventricular fibrillation could be reproducibly initiated with either one (4 dogs), two (5 dogs) or three extrastimuli (6 dogs). Diastolic excitability thresholds were 0.08 +/- 0.03, 0.30 +/- 0.17, and 0.09 +/- 0.04 mA (median +/- SD) for unipolar cathodal, anodal and bipolar pacing, respectively (p less than 0.001 for anodal vs. cathodal and bipolar). The median absolute current required for ventricular tachyarrhythmia initiation was also highest with anodal pacing (0.72 +/- 0.77 mA), versus both the cathodal and anodal modes (0.18 +/- 0.28 and 0.20 +/- 0.28 mA, respectively, each p less than 0.001) but was comparable in all three modes relative to the threshold current (2.0, 2.4 and 2.6 mA for cathodal, anodal and bipolar pacing, respectively) required for initiation. Overall, ventricular tachyarrhythmia initiation was concordant in all three modes at 58/67 (87%) sites and discordant at only 9/67 (13%) sites (p less than 0.001). Moreover, there was no difference in either the pattern of arrhythmia initiated in each of the pacing modes with respect to ventricular tachycardia versus ventricular fibrillation, or in the median current required to initiate ventricular tachycardia (0.30 +/- 0.36 mA) versus ventricular fibrillation (0.31 +/- 0.44 mA; p greater than 0.1). Thus, ventricular tachyarrhythmia initiation was comparable in all three pacing modes with respect to overall success rate, number of ventricular extrastimuli required and the pattern of ventricular tachyarrhythmia initiated. Bipolar pacing with similar size anodal and cathodal electrodes appear to be appropriate for electrophysiologic ventricular tachyarrhythmia studies and are not likely to induce spurious arrhythmias resulting from stimulation at the anodal pole.

Splanchnic extraction of oestrone and oestradiol and production of oestrone sulphate in man

The plasma concentrations of oestrone (Oe1), oestradiol (Oe2) and oestrone sulphate (Oe1S) were measured in the femoral artery (FA), femoral vein (FV) and hepatic vein (HV) in seven men and three postmenopausal women undergoing catheterization for the evaluation of cardiac arrhythmias. None of the persons had congestive heart failure; conventional liver function tests were normal, and they were without any medication. The plasma concentration (mean +/- SD) for Oe1 was 34.6 +/- 19.5 pM in HV, 134 +/- 71.6 pM in FV and 93.4 +/- 48.5 pM in FA. The plasma concentration of Oe2 was 29.9 +/- 19.7 pM in HV, 80.3 +/- 42.7 pM in FV and 55.2 +/- 28.1 pM in FA. The results support the concept of peripheral formation of Oe1 and Oe2 and hepatic removal. The plasma concentration of Oe1S was 980 +/- 469 pM in HV, 945 +/- 463 pM in FV and 937 +/- 461 pM in FA. The small difference in plasma level of Oe1S between FA and FV was insignificant. In all persons the plasma level of Oe1S was higher in HV than in FA and FV (2P less than 0.01) indicating a net formation of Oe1S in the splanchnic area.

Hypertrophic cardiomyopathy in three generations of a large Norwegian family. A clinical, echocardiographic, and genetic study

Hypertrophic cardiomyopathy is a heart muscle disease with an obscure aetiology. Data from four generations of a large family (71 members) are presented. The occurrence of hypertrophic cardiomyopathy among members of the two oldest generations was compatible with a pattern of autosomal dominant inheritance. Seven out of 14 siblings in the second generation had definite signs of or were clinically suspected of having hypertrophic cardiomyopathy. The severity and distribution of left ventricular hypertrophy varied, but three (21%) brothers in generation II showed the classic picture of left ventricular outflow obstruction. Four siblings (29%) died suddenly aged 11, 22, 38, and 40 years. A high incidence of the disease would have been expected in the two younger generations (41 members, aged 1-31 years), but only two, a 16 year old boy and a 17 year old girl had signs of asymmetric septal hypertrophy. Current diagnostic procedures, including M mode and cross sectional echocardiography, are not sufficiently sensitive to identify young family members who may have preclinical hypertrophic cardiomyopathy. No evidence for close genetic linkage between a postulated locus for hypertrophic cardiomyopathy and the major histocompatibility complex (antigens HLA-A, HLA-B, and HLA-DR) was found.

A time-related study of the hemodynamic benefit of atrioventricular synchronous pacing evaluated by Doppler echocardiography

We have used Doppler echocardiography to estimate the stroke volume (SV) in a study of 13 patients equipped with DDD pacemakers. SV was measured both during DDD and VVI pacing after observation times of 1,3,6, and 12 months of DDD pacing. SV was also measured at seven atrioventricular (AV) intervals (75-250 ms) in the search for optimal AV intervals. Mitral flow velocity was investigated to see if DDD pacing resulted in synchronous atrial contraction, and if mitral insufficiency existed at any of the pacing modes. Compared with the VVI mode, DDD pacing resulted in a mean increase in SV of 21 +/- 2% for the four observation periods. Two patients with severe left ventricular failure had no significant increase in SV during DDD vs VVI pacing. In each patient, an optimal AV interval ranging between 100-250 ms for the SV was found. Velocity profiles of mitral flow showed synchronous atrial contraction during DDD pacing, but not during VVI pacing. Mitral insufficiency was not seen in any pacing mode. DDD pacing resulted in a reduction in SV during the first 6 months, and was constant thereafter. Doppler echocardiography can be used repeatedly to evaluate the hemodynamic response of DDD pacing vs VVI pacing, and to find which AV interval gives the highest SV in the individual patient. Our study further shows that the hemodynamic benefit of DDD pacing is present after short-term as well as after long-term DDD pacing.

Importance of the pacing mode in the initiation of ventricular tachyarrhythmia in a canine model of chronic myocardial infarction

The use of unipolar anodal or bipolar pacing, as compared with unipolar cathodal pacing, purportedly increases the likelihood of inducing inadvertent ventricular fibrillation in susceptible patients. In this study, the ability to initiate sustained ventricular tachycardia or fibrillation with unipolar cathodal, unipolar anodal and bipolar pacing modes was compared using programmed ventricular stimulation at 82 subendocardial periinfarction sites in 11 dogs with chronic myocardial infarction. The late diastolic excitability threshold was significantly higher and the ventricular refractory period was significantly shorter (p less than 0.001) with anodal pacing (mean 0.62 mA, 156 ms, respectively) than with pacing in either the cathodal (0.12 mA, 174 ms) or the bipolar (0.13 mA, 173 ms) mode. At a current intensity twice that of the excitability threshold, the introduction of one or two extrastimuli induced ventricular tachycardia and ventricular fibrillation comparably among the three pacing modes. However, when three extrastimuli were used, ventricular fibrillation was induced with anodal pacing twice as frequently (50 [61%] of 82 sites) as with either of the other two pacing modes (each 23 [28%] of 82 sites, p less than 0.001), whereas the induction of ventricular tachycardia remained comparable with anodal pacing (15 [18%] of 82 sites) and cathodal and bipolar pacing (each 14 [17%] of 82 sites). Furthermore, a similarly high incidence of inducibility of ventricular fibrillation was observed with both cathodal pacing (56 [68%] of 82 sites) and bipolar pacing (40 [49%] of 82 sites) when an increased current equal to twice the anodal excitability threshold (1.23 mA) was used.(ABSTRACT TRUNCATED AT 250 WORDS)