Complete heart block

Complete heart block or complete AV block is a situation in which the sinus impulses are not conducted to the ventricles through the AV node. Hence the P waves and QRS complexes are dissociated (AV dissociation). The four cardinal features of complete heart block on the ECG are: 1) Regular PP interval (2) Regular RR interval (3) Varying PR interval (4) PP interval shorter than RR interval (atrial rate more than the ventricular rate). The QRS complexes can be either normal or wide, depending on the location of the block whether it is below the bundle of His (infra Hisean) or above it (supra Hisean). In supra Hisean block, the ventricles are controlled by a junctional focus and hence the QRS is narrow, while in infra Hisean block, the subsidiary pacemaker is ventricular, producing a wide QRS. Infra Hisean block has a poorer prognosis because the subsidiary ventricular focus is usually unstable and prone for Stokes-Adams attacks. A reversible cause of complete heart block is an indication for temporary pacing while a permanent one needs permanent pacing. Initial response to atropine may be checked under cardiac monitoring. Infra Hisean blocks do not respond to atropine and needs isoprenaline infusion to accelarate the ventricular focus. Temporary transcutaneous (non-invasive) pacing is an option to tide over a crisis till trans venous pacing can be arranged.