HIS BUNDLE ANALYSER

Typical Number in Hospital: 1

Cost Bands: 4

References: 3

The bundle of His (pronounced 'hiss') is a nerve trunk connecting the atrioventricular (AV) node in the heart to the main muscles and Purkinje fibres of the ventricles. A His bundle electrocardiogram (HBE) would show the point in time at which the AV node was first stimulated, and the point at which it in turn stimulates the His bundle, and then the contraction of the ventricles. In electronic terms the sequence of events from the natural pacemaker in the heart (the sinoatrial (SA) node) is like an astable multivibrator, followed by a delay line to the AV node which acts as a monostable delay mechanism to trigger the His bundle which again acts as a delay line feeding the signals to the muscles. The timing of these events is important to cause the upper and lower chambers of the heart to contract in the correct sequence.

Transmission along the His bundle may be defective in some cases, and it is possible to trace the path of the signal using a special-purpose analyser. Basically this consists of a stimulating probe and a pick-up probe by which a small pulse of electric current can be presented to the bundle through its surface and this can be detected at more distant points of the bundle. The presence of and timing of the arrival of the transmitted pulse are displayed and used to assess the extent and location of the defect.

Since the bundle of His is only accessible during cardiac surgery, this is a rather specialized device only likely to be used in heart surgery.