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The study investigates the response of atrial natriuretic peptide (ANP) to different cardiac pacing modes in comparison with hemodynamic changes. Ten patients underwent Swan-Ganz catheterization during pacemaker implant. Atrioventricular and ventricular pacing were performed consecutively at three pacing rate levels (80, 100, and 110 ppm). Blood samples were taken from the pulmonary artery for ANP determination, both basally and at the end of each pacing period. Concomitantly, mean pulmonary capillary wedge pressure (PCWP) and mean pulmonary artery pressure (PAP) were measured. Cardiac output (CO) was determined by thermodilution both basally and during the 110 ppm steps. During atrioventricular pacing, whereas no significant changes were observed for ANP, PCWP and PAP, CO increased significantly (P less than 0.0005). At the beginning of ventricular pacing hemodynamic parameters and ANP levels were comparable with those of baseline conditions. During subsequent ventricular pacing PCWP and ANP increased significantly at the 110 ppm rate step (P less than 0.05). PAP did not change significantly, whereas CO decreased in all cases (P less than 0.01). A positive correlation was observed between ANP and PCWP during ventricular (P less than 0.001), but not atrioventricular pacing. The results, while confirming the hemodynamic advantages of atrioventricular pacing, point to a major stimulation of ANP secretion during ventricular pacing. This fact, together with the observed drop in CO and the correlation between ANP and PCWP, suggest that the increase of ANP in ventricular pacing may be the expression of a compensatory mechanism to the hemodynamic disadvantages of atrioventricular asynchrony.

Eighty-two patients, with electrodes implanted for varying periods of time, have been divided into three groups: acute (at implantation); intermediate (3 to 36 months) and chronic (37 to 124 months). In these groups, respectively 28, 26 and 28 myocardial stimulation threshold measurements have been performed. Measurements have been performed with MEEMR (Myocardial Excitation Energy Meter), an instrument deviced and built by the Institute of Elaboration of Information, CNR and University of Pisa. Microjoule has been chosen as unit of measure. More commonly used units of measure, such as threshold current in milliamp, have been calculated from values in microjoules. Mean values was 0.6 muJ in the first group, 6.9 muJ in the second one and 8.3 in the third one. Student test has been performed on such measurements, divided into groups, with the following results: p less than 0.01 between 1st and 2nd group, non significant difference between 2nd and 3rd group, p less than 0.01 between 1st and 3rd group. Such results suggest a trend toward myocardial threshold stabilization over a long period of time, as had already been hypothized by others Authors. Further useful information may be drawn from these data if they are evaluated in relation to a life-time pacemaker, as is nowadays desirable in view of recent progress in circuit technology and energy sources.

The Authors have studied the vectocardiogram in left bundle branch block, right endoventricular pacing, myocardial infarction and right endoventricular pacing, myocardial infarction and left bundle branch block. Vectocardiographic loop analysis allows the diagnosis of myocardial infarction both in the presence of endoventricular pacing and in the presence of left bundle branch block.

According to a recent national survey, 387 patients were treated by permanent pacing in 10 Italian centers, between 1961 and 1966. Of these patients 205 have died; 131 (77 males and 54 females) are still alive and no informations could be obtained for the remaining 51 (13%). The overall survival of patients treated during this period of time is therefore not less than 34% which is comparable to that of general population of the same age group. The 131 patients still alive have totaled 1,486 years of pacing and have used up to 784 pacers. Comparing the incidence of the most common causes for replacement during the periods 1961-66 and 1973-77, electrode failures dropped from 21 to 0.9%; circuitry malfunctions occurred in 10.5 and 7.8%; battery depletion rose from 36.8 to 69% of the cases. According to their clinical conditions, the 131 patients on long-term follow-up can be grouped as follows: 62% are in class 1 or 2 of NYHA; 26.7% are in class 3, and 3.8% in class 4. Moreover, 53.4% of patients are living an active life, having some sort of occupation and 29% are holding a driving license.

A case of superior vena cava syndrome is described in a patient with two endocardial pacing electrodes. At autopsy a severe stenosis of the venous lumen was found at the crossing site of the two catheters. There was no evidence of thrombus formation. Venous wall stenosis is an unusual complication of transvenous pacing and is probably favoured by the presence of two electrodes.

Isotope venography was used to study the venous circulation proximal to the superior vena cava in two groups of pacemaker patients, one with a single endocavitary electrode and the other with multiple pacing catheters. A control group of patients without pacemakers was also studied. Numerous abnormalities were found, especially in the group with multiple electrodes. These findings suggest that venous obstruction is a common complication of endocardial pacing.

Experience with about 1500 electrostimulated patients is reported. Rather than give statistical data we have preferred to go briefly through the problems encountered in the course of our experience and suggest possible solutions. We have emphasized the following aspects: ventricular-triggered pacemaker, stimulation threshold, haemodynamic behaviour of the paced patient, problems concerning implanted pacemakers follow-up. Our 13 years experience has opened new prospects which deserve further study, such as programmable pacemakers, optimal generator life and a few important aspects in follow-up techniques.