Abstract: Methods and systems for transvenously accessing the pericardial space via the vascular system and atrial wall, particularly through the superior vena cava and right atrial wall, to deliver treatment in the pericardial space are disclosed. A steerable instrument is advanced transvenously into the right atrium of the heart, and a distal segment is deflected into the right atrial appendage. A fixation catheter is advanced employing the steerable instrument to affix a distal fixation mechanism to the atrial wall. A distal segment of an elongated medical device, e.g., a therapeutic catheter or an electrical medical lead, is advanced through the fixation catheter lumen, through the atrial wall, and into the pericardial space. The steerable guide catheter is removed, and the elongated medical device is coupled to an implantable medical device subcutaneously implanted in the thoracic region. The fixation catheter may be left in place.

Abstract: Atrial refractory and ventricular inhibit functions are independently implemented in an atrial-synchronized pacer. Spontaneous signals on the ventricular lead inhibit ventricular stimulation for a predetermined interval independent of the atria, except when there is noise on the ventricular lead. The atrial-based pacing logic establishes the usual refractory period following spontaneous P-waves, and when noise is detected on the atrial lead, the pacing logic reverts to a fixed atrial rate. The ventricular-inhibited logic includes a retriggerable noise timing circuit and a non-retriggerable inhibit timing circuit both triggered by the output of the ventricular sense amplifier. The output of the inhibit circuit disables the ventricular stimulation output circuit. However, if the output of the noise circuit stays high for an interval indicative of electromagnetic interference, the trigger input to the inhibit timing circuit is disabled to permit ventricular stimulation.