Fig 1.
(A) External pacing wires are switched at the pacemaker´s inputs. The pacemaker senses ventricular depolarization via the atrial channel and stimulates the atria before the next QRS complex, modified from [6]. (B) Original electrocardiogram during AVT pacing in a 3-month-old child with postoperative JET. A: atrial input, V: ventricular input, PM: external pacemaker, VS: ventricular sensing, AP: atrial pacing, AV: atrioventricular, PVARP: postventricular atrial refractory period.
Fig 2.
The custom-made JET simulator.
JET rates are selected via a rotary switch in the middle of one face. Signals for an ECG monitor are provided at the lateral output sites. Output plugs at the top supply the input signal for the pacemaker. An on/off switch is located at the right side of the device. R: right, L: left, F: foot, N: neutral.
Fig 3.
The model is composed of the JET-Simulator, an ECG monitor, a simulation doll, and an external AVT capable pacemaker. The doll is fitted with atrial and ventricular external pacing wires, simulating an infant after cardiac surgery.
Fig 4.
The MetaPost AP-VS-Visualizer.
A short software script utilizes the patient´s heart rate (JET simulator rate) and the AV delay as adjusted by the tester to calculate and graphically to display the interval between atrial pacing and sensing of the subsequent QRS complex. AP: atrial pacing, VS: ventricular sensing, AV: atrioventricular, bpm: beats per minute, ms: milliseconds, mV: millivolt.
Fig 5.
Ten pediatric cardiologists were asked to establish AVT pacing. Ten working steps were assessed: ON, switching on the pacemaker; VDD, choosing the VDD mode; V-SENSE, adjusting ventricular sensing for maximal insensitivity; MTR, selecting the maximal tracking rate at a value 10–20 bpm above the patient´s heart rate; AV-DLY, setting the AV delay to the maximum allowed value; PVARP, adjusting the post ventricular atrial refractory period to 100 ms; RATE, selecting a basic stimulation rate clearly below the patient´s heart rate; R-WAVE, measuring the ventricular input signal; A-SENSE, selecting an atrial sensitivity 50% of the ventricular input signal; WIRES, connecting the pacing wires of the pacemaker. Three points indicate perfect, 2 points suboptimal performance, and 1 point a mistake that impairs safe or effective AVT pacing.