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One of the most important problems in rate responsive (RR) pacing is the clinical experimental evaluation of the reliability of various sensors. In particular, it is difficult to test their sensitivity and specificity during daily activity of the patients. Atrial rate, when present and normal, is the most physiological marker of metabolic requirements, but sometimes it is impossible to analyze the P wave in ventricular paced rhythm during routinely performed tests (e.g., ergometric test and 24-hour Holter monitoring). During various physical activities, we monitored atrial electrograms on an esophageal lead on the first channel of a standard Holter tape recorder; on the second channel a surface ECG lead was recorded. We selected 10 patients with high grade heart block and normal sinus node function paced in RR-VVI mode. RR pacing was obtained using various sensors (body activity, blood temperature, spike-T interval, minute ventilation). The good quality of recording allowed an easy evaluation of atrial and ventricular rates. In four cases an appropriate increase in heart rate was documented; sensitivity threshold and/or rate response slope were reprogrammed when indicated. The pacing rate of one patient did not parallel the atrial rate during walking only. In three cases, we observed a delay in the ventricular rate increase, with ventricular rate decreasing at peak exercise despite further atrial rate increase. In the last two patients, we observed inappropriate pacing response; pacing rate increased later and to a lower level than the atrial one. This new method is applied easily and appears reliable to evaluate the response of RR pacemakers to individual metabolic needs.(ABSTRACT TRUNCATED AT 250 WORDS)

Superior vena cava obstruction is described in a patient with two endocardial pacing electrodes. At necropsy a severe stenosis of the venous lumen was found at the site of intersection 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.

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.