Adrian Pietersen

Lesion dimensions during temperature-controlled radiofrequency catheter ablation of left ventricular porcine myocardium: impact of ablation site, electrode size, and convective cooling.

BACKGROUND It is important to increase lesion size to improve the success rate for radiofrequency ablation of ischemic ventricular tachycardia. This study of radiofrequency ablation, with adjustment of power to approach a preset target temperature, ie, temperature-controlled ablation, explores the effect of catheter-tip length, ablation site, and convective cooling on lesion dimensions. METHODS AND RESULTS In vitro strips of porcine left ventricular myocardium during different levels of convective cooling and in vivo pig hearts at 2 or 3 left ventricular sites were ablated with 2- to 12-mm-tip catheters. We found increased lesion volume for increased catheter-tip length </=8 mm in vitro (P<0.05) and 6 mm in vivo (P<0. 0001), but no further increase was found for longer tips. For the 4- to 10-mm catheter tips, we found smaller lesion volume in low-flow areas (apex) than in high-flow areas (free wall and septum) (P<0.05). Increasing convective cooling of the catheter tip in vitro increased lesion volume (P<0.0005) for the 4- and 8-mm tips but not for the 12-mm tip as the generator reached maximum output. In contrast to power-controlled ablation, we found a negative correlation between tip temperature reached and lesion volume for applications in which maximum generator output was not achieved (P<0. 0001), whereas delivered power and lesion volume correlated positively (P<0.0001). CONCLUSIONS Lesion size differs in different left ventricular target sites, which is probably related to convective cooling, as illustrated in vitro. Longer electrode tips increase lesion size for tip lengths </=6 to 8 mm. For temperature-controlled ablation, the tip temperature achieved is a poor predictor of lesion size.

Usefulness of flecainide for prevention of paroxysmal atrial fibrillation and flutter

To evaluate the efficacy of flecainide acetate in the prevention of paroxysmal atrial fibrillation and flutter, 43 patients (23 men) (mean age 53 years) were randomized blindly to receive either placebo or 150 mg of flecainide twice per day for consecutive periods of 3 months. Attacks were verified by a minielectrocardiogram event recorder. If intolerable symptoms developed, the protocol allowed patients to cross over between treatments before the end of the first 3-month period. Four patients crossed over prematurely, between 1 week and 1 month, and 15 between 1 month and 3 months. The remaining 24 patients completed both 3-month periods. In all 3 treatment intervals, there was a significant reduction in the number of attacks during flecainide treatment (p less than 0.002). Complete suppression was seen in 15 of 43 patients (35%) treated with flecainide for 1 week, in 18 of 39 (46%) treated for 1 month and in 12 of 24 (50%) completing all 3 months in each period. Adverse effects were reported in 32 of the 43 patients (74%) treated with flecainide, but only 2 were withdrawals. One patient died suddenly. In comparison, 3 of 43 patients (7%) reported adverse effects in the placebo group. In conclusion, flecainide significantly suppressed the number of attacks of paroxysmal atrial fibrillation and flutter. Adverse effects were frequent but were mostly tolerable.

Tissue Temperatures and Lesion Size During Irrigated Tip Catheter Radiofrequency Ablation: An In Vitro Comparison of Temperature-Controlled Irrigated Tip Ablation, Power-Controlled Irrigated Tip Ablation, and Standard Temperature-Controlled Ablation

The limited success rate of radiofrequency catheter ablation in patients with ventricular tachycardias related to structural heart disease may be increased by enlarging the lesion size. Irrigated tip catheter ablation is a new method for enlarging the size of the lesion. It was introduced in the power‐controlled mode with high power and high infusion rate, and is associated with an increased risk of crater formation, which is related to high tissue temperatures. The present study explored the tissue temperatures during temperature‐controlled irrigated tip ablation, comparing it with standard temperature‐controlled ablation and power‐controlled irrigated tip ablation. In vitro strips of porcine left ventricular myocardium were ablated. Temperature‐controlled irrigated tip ablation at target temperatures 60°C, 70°C, and 80°C with infusion of 1 mL saline/min were compared with standard temperature‐controlled ablation at 70°C and power‐controlled irrigated tip ablation at 40 W, and infusion of 20 mL/min. Lesion size and tissue temperatures were significantly higher during all modes of irrigated tip ablation compared with standard temperature‐controlled ablation (P < 0.05). Lesion volume correlated positively with tissue temperature (r = 0.87). The maximum recorded tissue temperature was always 1 mm from the ablation electrode and was 67 ± 4°C for standard ablation and 93 ± 6°C, 99 ± 6°C, and 115 ± 13°C for temperature‐controlled irrigated tip ablation at 60°C, 70°C, and 80°C, respectively, and 112 ± 12°C for power‐controlled irrigated tip ablation, which for irrigated tip ablation was significantly higher than tip temperature (P < 0.0001). Crater formation only occurred at tissue temperatures > 100°C. We conclude that irrigated tip catheter ablation increases lesion size and tissue temperatures compared with standard ablation in the temperature‐controlled mode at the same or higher target temperatures and in the power‐controlled mode. Furthermore, tissue temperature and delivered power are the best indicators of lesion volume during temperature‐controlled ablation.

J-shaped association between QTc interval duration and the risk of atrial fibrillation: results from the Copenhagen ECG study.

OBJECTIVES The aim of this study was to investigate whether the heart rate-corrected QT (QTc) interval on the electrocardiogram (ECG) is associated with the onset of atrial fibrillation (AF). BACKGROUND Patients with hereditary short-QT or long-QT syndromes, representing the very extremes of the QT interval, both seem to have a high prevalence of AF. METHODS A total of 281,277 subjects were included, corresponding to one-third of the population of the greater region of Copenhagen. These subjects underwent digital ECG recordings in a general practitioners core facility from 2001 to 2010. Data on drug use, comorbidities, and outcomes were collected from Danish registries. RESULTS After a median follow-up period of 5.7 years, 10,766 subjects had developed AF, of whom 1,467 (14%) developed lone AF. Having a QTc interval lower than the first percentile (≤372 ms) was associated with a multivariate-adjusted hazard ratio of 1.45 (95% confidence interval: 1.14 to 1.84; p = 0.002) of AF, compared with the reference group (411 to 419 ms). From the reference group and upward, the risk of AF increased with QTc interval duration in a dose-response manner, reaching a hazard ratio of 1.44 (95% confidence interval: 1.24 to 1.66, p < 0.001) for those with QTc intervals ≥99th percentile (≥464 ms). The association with respect to longer QTc intervals was stronger for the outcome of lone AF, as evidenced by a hazard ratio of 2.32 (95% confidence interval: 1.52 to 3.54, p < 0.001) for having a QTc interval ≥99th percentile (≥458 ms). CONCLUSIONS In this large ECG study, a J-shaped association was found between QTc interval duration and risk of AF. This association was strongest with respect to the development of lone AF.

Temperature-controlled irrigated tip radiofrequency catheter ablation: comparison of in vivo and in vitro lesion dimensions for standard catheter and irrigated tip catheter with minimal infusion rate

Temperature‐Controlled Irrigated Tip Ablation. Introduction: In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, hut has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature‐ controlled mode, target temperature 60°C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80°C.

Risk of atrial fibrillation as a function of the electrocardiographic PR interval: Results from the Copenhagen ECG Study

BACKGROUND Prolongation of the PR interval has been associated with an increased risk of incident atrial fibrillation (AF). OBJECTIVE To determine if there was a nonlinear relation between PR interval duration and the risk of AF. METHODS We included 288,181 individuals, corresponding to one third of the population in the greater region of Copenhagen. These individuals had a digital electrocardiogram (ECG) recorded in a general practitioners core facility from 2001 to 2010. Data on drug use, comorbidity, and outcomes were collected from Danish registries. RESULTS During a median follow-up period of 5.7 years, 11,087 developed AF. Having a PR interval ≥95th percentile (≥196 ms for women, ≥204 ms for men) was associated with an increased risk of AF as evidenced by a multivariable-adjusted hazard ratio (HR) of 1.18 (95% confidence interval [CI] 1.06-1.30, P = .001) for women and 1.30 (1.17-1.44, P < .001) for men compared with the respective reference groups (PR interval between 40th and 60th percentile). Having a short PR interval <5th percentile (≤121 ms for women, ≤129 ms for men) was also associated with an increased risk of AF for women (HR 1.32, 95% CI 1.12-1.56, P = .001), but this was not significant for men (HR 1.09, 95% CI 0.92-1.29, P = .33). CONCLUSION In this large ECG study, we found an increased risk of AF for longer PR intervals for both women and men. With respect to short PR intervals, we also observed an increased risk of AF for women.

Risk prediction of cardiovascular death based on the QTc interval: evaluating age and gender differences in a large primary care population

Aims Using a large, contemporary primary care population we aimed to provide absolute long-term risks of cardiovascular death (CVD) based on the QTc interval and to test whether the QTc interval is of value in risk prediction of CVD on an individual level. Methods and results Digital electrocardiograms from 173 529 primary care patients aged 50–90 years were collected during 2001–11. The Framingham formula was used for heart rate-correction of the QT interval. Data on medication, comorbidity, and outcomes were retrieved from administrative registries. During a median follow-up period of 6.1 years, 6647 persons died from cardiovascular causes. Long-term risks of CVD were estimated for subgroups defined by age, gender, cardiovascular disease, and QTc interval categories. In general, we observed an increased risk of CVD for both very short and long QTc intervals. Prolongation of the QTc interval resulted in the worst prognosis for men whereas in women, a very short QTc interval was equivalent in risk to a borderline prolonged QTc interval. The effect of the QTc interval on the absolute risk of CVD was most pronounced in the elderly and in those with cardiovascular disease whereas the effect was negligible for middle-aged women without cardiovascular disease. The most important improvement in prediction accuracy was noted for women aged 70–90 years. In this subgroup, a total of 9.5% were reclassified (7.2% more accurately vs. 2.3% more inaccurately) within clinically relevant 5-year risk groups when the QTc interval was added to a conventional risk model for CVD. Conclusion Important differences were observed across subgroups when the absolute long-term risk of CVD was estimated based on QTc interval duration. The accuracy of the personalized CVD prognosis can be improved when the QTc interval is introduced to a conventional risk model for CVD.

P-wave duration and the risk of atrial fibrillation: Results from the Copenhagen ECG Study

BACKGROUND Results on the association between P-wave duration and the risk of atrial fibrillation (AF) are conflicting. OBJECTIVE The purpose of this study was to obtain a detailed description of the relationship between P-wave duration and the risk of AF. METHODS Using computerized analysis of electrocardiograms from a large primary care population, we evaluated the association between P-wave duration and the risk of AF. Secondary end-points were death from cardiovascular causes and putative ischemic stroke. Data on drug use, comorbidity, and outcomes were collected from administrative registries. RESULTS A total of 285,933 individuals were included. During median follow-up period of 6.7 years, 9550 developed AF, 9371 died of a cardiovascular cause, and 8980 had a stroke. Compared with the reference group (100-105 ms), individuals with very short (≤89 ms; hazard ratio [HR] 1.60, 95% confidence interval [CI] 1.41-1.81), intermediate (112-119 ms; HR 1.22, 95% CI 1.13-1.31), long (120-129 ms; HR 1.50, 95% CI 1.39-1.62), and very long P-wave duration (≥130 ms; HR 2.06, 95% CI 1.89-2.23) had an increased risk of incident AF. With respect to death from cardiovascular causes, we found an increased risk for very short (≤89 ms; HR 1.20, 95% CI 1.06-1.34), long (120-129 ms; HR 1.11, 95% CI 1.04-1.19), and very long P-wave duration (≥130 ms; HR 1.30, 95% CI 1.21-1.40) compared with the reference group (106-111 ms). Similar but weaker associations were found between P-wave duration and the risk of putative ischemic stroke. CONCLUSION In a large primary care population we found both short and long P-wave duration to be robustly associated with an increased risk of AF.

Atrial fibrillation in the Wolff-Parkinson-White syndrome

Atrial fibrillation in patients with Wolff-Parkinson-White (WPW) syndrome may lead to syncope, ventricular fibrillation, and sudden death. In a follow-up study of 241 patients with WPW syndrome in a relatively unselected population, 26 patients had documented atrial fibrillation (11%). These patients were followed up after 1-37 years (median 11 years; mean 15 years). During this period, 2 of 26 died suddenly. These 2 patients had the shortest RR interval during spontaneous atrial fibrillation (less than or equal to 220 msec), greater than or equal to 1 episodes of syncope, and a persistent delta wave in all available electrocardiograms. In comparison, sudden or tachycardia-related death was seen in 4 of the 241 patients. This difference is not statistically significant. Thus, atrial fibrillation of 26 patients with WPW syndrome was surprisingly well tolerated in our follow-up study with only 2 sudden deaths.

Temperature-controlled Radiofrequency Ablation of Cardiac Tissue: An In Vitro Study of the Impact of Electrode Orientation, Electrode Tissue Contact Pressure and External Convective Cooling

Background: A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size.Methods and Results: In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 °C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size.Conclusions: During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.