Atrioventricular Interval

The AVI, often poorly understood, should be considered a single interval with two subportions (Fig. 6.16A).17 For most dual-chamber systems, the atrial

Figure 6.16. A: The AVI should be considered as a single interval with two subportions. The entire AVI corresponds to the programmed value, that is, the interval following a paced or sensed atrial beat allowed before a ventricular pacing artifact is delivered. The initial portion of the AVI is the blanking period. This interval is followed by the crosstalk sensing window. B: If the ventricular sensing circuit senses activity during the crosstalk sensing window, a ventricular pacing artifact is delivered early, usually at 100 to 110 milliseconds after the atrial event. This has been referred to as "ventricular safety pacing," "110-millisecond phenomenon," and "nonphysiologic AV delay." C: The initial portion of the AVI in most dual-chamber pacemakers is designated as the blanking period. During this portion of the AVI, sensing is suspended. The primary purpose of this interval is to prevent ventricular sensing of the leading edge of the atrial pacing artifact. Any event that occurs during the blanking period, even if it is an intrinsic ventricular event (as shown in this figure), is not sensed. In this example, the ventricular premature beat that is not sensed is followed by a ventricular pacing artifact delivered at the programmed AVI and occurring in the terminal portion of the T wave.

Figure 6.16. A: The AVI should be considered as a single interval with two subportions. The entire AVI corresponds to the programmed value, that is, the interval following a paced or sensed atrial beat allowed before a ventricular pacing artifact is delivered. The initial portion of the AVI is the blanking period. This interval is followed by the crosstalk sensing window. B: If the ventricular sensing circuit senses activity during the crosstalk sensing window, a ventricular pacing artifact is delivered early, usually at 100 to 110 milliseconds after the atrial event. This has been referred to as "ventricular safety pacing," "110-millisecond phenomenon," and "nonphysiologic AV delay." C: The initial portion of the AVI in most dual-chamber pacemakers is designated as the blanking period. During this portion of the AVI, sensing is suspended. The primary purpose of this interval is to prevent ventricular sensing of the leading edge of the atrial pacing artifact. Any event that occurs during the blanking period, even if it is an intrinsic ventricular event (as shown in this figure), is not sensed. In this example, the ventricular premature beat that is not sensed is followed by a ventricular pacing artifact delivered at the programmed AVI and occurring in the terminal portion of the T wave.

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