Cryothermal mapping of the sinus node in dogs: a simple method of localising dominant and latent pacemakers

To investigate the potential use of cryothermal mapping to localise the sites of the dominant and latent pacemakers of the sinus node, we compared the results of cryothermal and electrical mapping of the sinus node in 16 dogs. In all dogs, cooling (−5 to +5°C) of a localised epicardial area of about 3 × 3 mm2 close to the sulcus terminalis (area 1) resulted in a decrease in heart rate and a change in the P wave configuration. Cooling of an additional area of up to 15 × 3 mm2 (area 2) while cooling of area 1 was maintained resulted in a further decrease in heart rate and a further change in P wave configuration until junctional rhythm occurred. In all dogs areas 1 and 2 could be identified within 5 min. The heart rate and P wave configuration returned to control following cooling suggesting no adverse effect of cooling on the sinus node in this temperature range. In dogs with sufficiently slow heart rates, recording from area 1 showed diastolic and upstroke slopes followed by primary negativity, indicating that area 1 was the area of the dominant pacemaker. Recording from area 2 showed only diastolic slopes indicating that area 2 was the area of the latent pacemaker. Compared to electrical mapping for identifying diastolic slope, upstroke slope and primary negativity or earliest atrial activation, cryothermal mapping is a simple, quick and safe procedure for localisation of the sinus pacemakers. Unlike recording of sinus nodal electrograms, cryothermal mapping can be performed in the presence of rapid heart rates. Clinical application of the technique during cardiac surgery may help prevent damage to the sinus node and reduce the incidence of postoperative sinus node dysfunction.