Simultaneous Biventricular Noncontact Mapping (SBNM) of Ventricular Tachycardia (VT) in a Chronic Model of Ovine Myocardial Infarction (MI)

310 Simultaneous Biventricular Noncontact Mapping (SBNM) of Ventricular Tachycardia (VT) in a Chronic Model of Ovine Myocardial Infarction (MI) Jim Pouliopoulos ∗ , Gopal Sivagangabalan, Kaimin Huang, Tony Barry, Juntang Lu, Pramesh Kovoor Westmead Hospital, Sydney, NSW, Australia Background: Traditional single chamber noncontact mapping has limited ability to identify scar or map septal VT. Aims: To evaluate the ability of dynamic substrate mapping (DSM) to identify scar and assess SBNM in localising septal VT. Methods: Electrophysiological studies were performed in 15 survivors, 80 ± 61 weeks following percutaneously induced anterior MI (n = 20). Noncontact mapping was validated using 20–36 transmural multielectrode needles within and around scar in both ventricles and septum. DSM and inhouse developed alternative DSM (ADSM) were evaluated in 8 sheep without VT. SBNM was performed in 6/7 sheep with VT (cycle length 251 ± 33 ms) and correlated with needle electrograms. Scar was quantified histologically from each needle location. Results: ADSM showed improved reliability at delineating scar compared with DSM (p < 0.01) and corresponded with functional changes of conduction associated with scarring (increased threshold, conduction delay, p < 0.01). All sheep with VT had septal origin earliest left ventricular activation in four, and earlier right ventricular activation in two. Re-entry was confirmed with entrainment (PPI <20 ms). The SBNM activation sequence during entrainment from earliest chambers correlated with the VT sequence (early r = 0.9, late r = 0.2). Slowing of conduction during VT was significantly associated with decreased ADSM voltage (p < 0.001). The chamber that was activated later during VT had evidence of slow conduction during sinus rhythm (late chamber = −0.65 V s−1 ; early chamber = −0.52 V s−1 , p < 0.025). Conclusion: ADSM enabled rapid and accurate identification of scar. SBNM enables identification of septal VT. This should enable increased success in ablating VT with the ability of rapid and accurate delineation of scar and septal VT localization. doi:10.1016/j.hlc.2008.05.311

Abstracts

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CLINICAL – TRIALS 311 The Antiplatelet Effect of Higher Loading and Maintenance Dose Regimens of Clopidogrel: The Plavix Response in Coronary Intervention (PRINC) trial Patrick Gladding ∗ , Mark Webster, Irene Zeng, Helen Farrell, Jim Stewart, Peter Ruygrok, John Ormiston, Seif El-Jack, Guy Armstrong, Patrick Kay, Douglas Scott Green Lane Cardiovascular Service, Auckland City Hospital, Auckland, New Zealand Background: Clopidogrel loading doses above 600 mg have not resulted in more rapid or complete platelet inhibition. Methods: A double-blind, randomised, controlled trial was undertaken in 60 patients undergoing percutaneous coronary intervention. All patients received clopidogrel 600 mg at the start of the procedure. Using a 2 × 2 factorial design, patients were randomised to a second dose of clopidogrel 600 mg given 2 h later or matching placebo, and to verapamil 5 mg intra-arterial or placebo given at the time of PCI. Platelet inhibition was measured using the Accumetrics VerifyNow® P2Y12 platelet function analyzer at 2, 4, and 7 h from the first loading dose. The next day patients were further randomised to receive a clopidogrel maintenance dose of either 75 mg or 150 mg once daily, with platelet function assessed after 1 week. Results: Two hours after the second dose of clopidogrel or placebo, platelet inhibition was 42 ± 27% with clopidogrel, compared with 24 ± 22% with placebo, p = 0.0006. By 5 h after the second dose, platelet inhibition was 49 ± 30% with clopidogrel, compared with 29 ± 22% with placebo, p = 0.006. Verapamil given at the time of the first clopidogrel dose had no effect on clopidogrel pharmacodynamics. A clopidogrel maintenance dose of 150 mg daily for 1 week resulted in greater platelet inhibition than 75 mg daily (50 ± 28 versus 29 ± 19%, p = 0.01). Conclusion: A clopidogrel 1200 mg loading dose, given as two 600 mg doses 2 h apart, results in more rapid and complete platelet inhibition than a single 600 mg dose. A clopidogrel maintenance dose of 150 mg daily produces greater platelet inhibition than 75 mg daily. doi:10.1016/j.hlc.2008.05.312 312 Primary Prevention of Sudden Cardiac Death after ST Elevation Myocardial Infarction with Targeted Electrophysiological Study and Early Cardioverter-Defibrillator Implantation Sarah Zaman ∗ , Gopal Sivagangabalan, Arun Narayan, David Ross, Pramesh Kovoor Department of Cardiology, Westmead Hospital, Sydney, NSW, Australia We prospectively assessed the outcomes of our risk stratification strategies over a 41 month period in 689 consecutive patients, mean age 60 ± 12 years, treated for

ABSTRACTS

Heart, Lung and Circulation 2008;17S:S1–S209