An interventional medical system comprising an introducer sheath and an apparatus for forming a passageway through tissue in a body of a patient; the introducer sheath comprising a longitudinally extending lumen extending from a proximal opening thereof to a distal opening thereof, the lumen being sized to receive passage of the apparatus therethrough and out the distal opening thereof; and the apparatus comprising: a flexible elongate shaft extending over a length from a proximal end thereof to a distal end thereof, the shaft including a lumen extending from the proximal end to the distal end; a dilator mounted to the distal end of the shaft, the dilator including a proximal end, a distal end, a first portion, a second portion, and a longitudinally extending lumen, the first portion extending from the proximal end of the dilator to the second portion, the second portion extending from the first portion to the distal end of the dilator, the lumen of the dilator being in fluid communication with the lumen of the shaft and including a distal opening located at the distal end of the dilator; and characterized by:the first portion having an increasing taper from a first outer diameter, in proximity to the dilator proximal end, to a larger second outer diameter, in proximity to the second portion, the second portion having a decreasing taper from the first portion to the dilator distal end, and the second portion including an external non-cutting thread formed along the decreasing taper; and an elongate wire slideably engaged within the lumens of the shaft and dilator, the wire including a piercing distal tip; and wherein the lumen of the dilator has a nominal diameter that is smaller than a nominal diameter of the shaft lumen; and the lumen of the dilator includes a funnel-shaped entry, the dilator lumen extending from the entry thereof to the distal opening thereof. a flexible elongate shaft extending over a length from a proximal end thereof to a distal end thereof, the shaft including a lumen extending from the proximal end to the distal end; a dilator mounted to the distal end of the shaft, the dilator including a proximal end, a distal end, a first portion, a second portion, and a longitudinally extending lumen, the first portion extending from the proximal end of the dilator to the second portion, the second portion extending from the first portion to the distal end of the dilator, the lumen of the dilator being in fluid communication with the lumen of the shaft and including a distal opening located at the distal end of the dilator; and characterized by:the first portion having an increasing taper from a first outer diameter, in proximity to the dilator proximal end, to a larger second outer diameter, in proximity to the second portion, the second portion having a decreasing taper from the first portion to the dilator distal end, and the second portion including an external non-cutting thread formed along the decreasing taper; and an elongate wire slideably engaged within the lumens of the shaft and dilator, the wire including a piercing distal tip; and wherein the lumen of the dilator has a nominal diameter that is smaller than a nominal diameter of the shaft lumen; and the lumen of the dilator includes a funnel-shaped entry, the dilator lumen extending from the entry thereof to the distal opening thereof.