A treatment system for providing therapy to treat a heart rhythm disorder, the treatment system comprising: a body surface device configured to be worn by a subject, the body surface device comprising a plurality of sensing electrodes (435, 530, 535, 552) configured to detect electrical signals of a heart of the subject to generate a first set of signal data, the electrodes covering one or more spatial projections of one or more areas of a heart (220, 225, 230, 235, 240, 245, 250, 270, 275, 295, 525) projected on a body surface (360, 365, 420) of the subject; an internal catheter configured to be positioned within the heart or in contact with the heart, the internal catheter configured to detect electrical signals of the heart to generate a second set of signal data; and a computing device; characterised in that the computing device is configured to: conduct a directionality analysis using the first set and the second set of signal data, wherein conducting the directionality analysis comprises: generating a first directional vector from the first set of signal data detected by the body surface device; generating a second directional vector from the second set of signal data detected by the internal catheter; determining that a degree of similarity between the first directional vector and the second directional vector is below a threshold; and generating a guidance on the movement of the internal catheter using past records of the subject and data from a database of procedures; and guide a movement of the internal catheter towards a target tissue to treat a heart rhythm disorder based on the directionality analysis. a body surface device configured to be worn by a subject, the body surface device comprising a plurality of sensing electrodes (435, 530, 535, 552) configured to detect electrical signals of a heart of the subject to generate a first set of signal data, the electrodes covering one or more spatial projections of one or more areas of a heart (220, 225, 230, 235, 240, 245, 250, 270, 275, 295, 525) projected on a body surface (360, 365, 420) of the subject; an internal catheter configured to be positioned within the heart or in contact with the heart, the internal catheter configured to detect electrical signals of the heart to generate a second set of signal data; and a computing device; characterised in that the computing device is configured to: conduct a directionality analysis using the first set and the second set of signal data, wherein conducting the directionality analysis comprises: generating a first directional vector from the first set of signal data detected by the body surface device; generating a second directional vector from the second set of signal data detected by the internal catheter; determining that a degree of similarity between the first directional vector and the second directional vector is below a threshold; and generating a guidance on the movement of the internal catheter using past records of the subject and data from a database of procedures; and guide a movement of the internal catheter towards a target tissue to treat a heart rhythm disorder based on the directionality analysis. conduct a directionality analysis using the first set and the second set of signal data, wherein conducting the directionality analysis comprises: generating a first directional vector from the first set of signal data detected by the body surface device; generating a second directional vector from the second set of signal data detected by the internal catheter; determining that a degree of similarity between the first directional vector and the second directional vector is below a threshold; and generating a guidance on the movement of the internal catheter using past records of the subject and data from a database of procedures; and generating a first directional vector from the first set of signal data detected by the body surface device; generating a second directional vector from the second set of signal data detected by the internal catheter; determining that a degree of similarity between the first directional vector and the second directional vector is below a threshold; and generating a guidance on the movement of the internal catheter using past records of the subject and data from a database of procedures; and guide a movement of the internal catheter towards a target tissue to treat a heart rhythm disorder based on the directionality analysis.