Characterisation of ventricular activation through conventional mapping techniques has always been limited by the need for sequential mapping which is unsuitable for non-sustained or poorly tolerated rhythms. Non-contact mapping, with its ability to generate simultaneous, high resolution. isopotential maps from an entire cardiac chamber, enables characterisation of cardiac activation in the intact human heart to a detail not previously attainable. Characterisation of properties of the excitable gap of ventricular tachycardia (VT) circuits was performed by analysing the response to single programmed extrastimuli in an attempt to reset the circuit. The temporal and spatial properties of the EGap vary at different sites of entry to the circuit. The effects of single ventricular extrastimuli (SVE) preexciting such circuits are dependent on the degree of interval dependent conduction slowing (conduction in partially excitable myocardium) within the diastolic pathway or modification of functional block defining the circuit. All circuits could be preexcited over a range of SVE's, therefore failure to reset a tachycardia does not indicate the absence of an excitable gap and failure of entry to the circuit. Mapping and ablation of VT circuits was performed in 40 patients all with previous myocardial infarction. Non-contact mapping identified an exit site in 100% and diastolic pathway activity in 56% of VT and guided successful ablation in 88% of patients. VT recurrence necessitating ICD therapy was significantly reduced but new VT is seen probably reflecting the evolving underlying substrate. Using non-contact mapping, VT, exit site location was identified in 121 VT and compared with 12 lead ECG morphology during VT. A correlation, a positive predictive value of ~70%, was seen with 8 different ECG patterns, accounting for 57% of mapped VT. An algorithm was developed and tested prospectively which led to correct identification of 93% of VT exit sites. Non-contact mapping was used to characterise the timing and patterns of activation in 41 patients with remote myocardial infarction and impaired left ventricular function. Eighteen patients had normal QRS duration and 23 had left bundle branch block (LBBB). In patients with LBSB, the principal cause of QRS prolongation is not due to increased interventricular conduction but to increased intraventricular LV conduction time. Lack of benefit from cardiac resynchronization seen in a subset of patients may be due to this intraventricular conduction delay. Although ECG characteristics of LSBS do not correlate with sites of earliest or latest endocardial ventricular activation, they do identify a subset of patients with the longest intraventricular conduction delay.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:486336 |
| Date | January 2005 |
| Creators | Segal, Oliver R. |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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