The scar: the wind in the perfect storm-insights into the mysterious living tissue originating ventricular arrhythmias.

BACKGROUND: Arrhythmic death is very common among patients with structural heart disease, and it is estimated that in European countries, 1 per 1000 inhabitants yearly dies for sudden cardiac death (SCD), mainly as a result of ventricular arrhythmias (VA). The scar is the result of cardiac remodelling process that occurs in several cardiomyopathies, both ischemic and non-ischemic, and is considered the perfect substrate for re-entrant and non-re-entrant arrhythmias. METHODS: Our aim was to review published evidence on the histological and electrophysiological properties of myocardial scar and to review the central role of cardiac magnetic resonance (CMR) in assessing ventricular arrhythmias substrate and its potential implication in risk stratification of SCD. RESULTS: Scarring process affects both structural and electrical myocardial properties and paves the background for enhanced arrhythmogenicity. Non-uniform anisotropic conduction, gap junctions remodelling, source to sink mismatch and refractoriness dispersion are some of the underlining mechanisms contributing to arrhythmic potential of the scar. All these mechanisms lead to the initiation and maintenance of VA. CMR has a crucial role in the evaluation of patients suffering from VA, as it is considered the gold standard imaging test for scar characterization. Mounting evidences support the use of CMR not only for the definition of gross scar features, as size, localization and transmurality, but also for the identification of possible conducting channels suitable of discrete ablation. Moreover, several studies call out the CMR-based scar characterization as a stratification tool useful in selecting patients at risk of SCD and amenable to implantable cardioverter-defibrillator (ICD) implantation. CONCLUSIONS: Scar represents the substrate of ventricular arrhythmias. CMR, defining scar presence and its features, may be a useful tool for guiding ablation procedures and for identifying patients at risk of SCD amenable to ICD therapy.

A new echo-Doppler method to measure interatrial conduction time. Validation and clinical usefulness.

AIM: The aim of this study was to assess if knowing the interatrial conduction time is useful to better program atrioventricular delay in sequential pacing. The study proposes a new echo-Doppler method to measure interatrial conduction time, correlating it with electrophysiological measures. METHODS: The new method was tested in 30 subjects who underwent electrophysiological study. Interatrial conduction time by new method was taken during atrial pacing as the interval between the artefact of electrocardiogram pacing, shown on screen echo, and the onset of the A wave of the echo-Doppler mitral inflow. The electrophysiological measures were obtained, in the same subjects and at the same time, by a decapolar catheter in coronary sinus as intervals between the artefact of atrial pacing and the first positive left atrial deflection at proximal (C7C8) and distal (C1C2) electrodes. RESULTS: Echo-Doppler mean time was 114±12 ms, electrophysiological time was 107±14 ms at C7C8 and 124±11 ms at C1C2. Statistical analysis showed a good correlation (r=0.92, P<0.001) and accord (mean difference=6.6 ms) between the two methods. CONCLUSION: The new method to measure interatrial conduction time is consistent with the electrophysiological method; it could be particularly useful in programming the best AV delay in sequential and biventricular pacing, to avoid atrial contraction against a closed mitral valve.