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Accepted answer

As mentioned in the comments you can use the Highcharts SVGRenderer class to draw out a line. You can use something like a load event of Highcharts within which you can make use of the SVGRenderer to create a path line.

chart: {
     events: {
        load: function () {
                console.log(this.chart); // This will get tou the chart reference where in you can find the coordinates of the point from where you want to draw the line
var x1 = this.series[0].data[this.series[0].data.length - 1].plotX + this.plotLeft;
var y1 = this.series[0].data[this.series[0].data.length - 1].plotY + this.plotTop;
            var label = this.renderer.path(['M', x1,y1,'L', 550, y1])//M 75 223.5 L 593 223.5
        .attr({
                'stroke-dasharray': '2,2',
            'stroke-width': 2,
            stroke: 'red'
        })
        .add();
        var label = this.renderer.path(['M', 550, this.plotTop + this.plotHeight,'L', 550, y1])//M 75 223.5 L 593 223.5
        .attr({
                'stroke-dasharray': '2,2',
            'stroke-width': 2,
            stroke: 'red'
        })
        .add();


        }
    }
}

The x-coordinate 550, I selected randomly, but if you know the x-point then it is the way you do it. Here is the new fiddle link . Hope it helps


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