Inhomogeneity of Cellular Refractoriness in Human Atrium: Factor of Arrhythmia?

Spatial inhomogeneity of refractory periods, as measured during clinical electrophysiological studies, is a known predisposing factor of arrhythmia. We studied elective refractory periods (ERP) and action potential duration (ADP₉₀) on isolated human atrium. Twelve samples of right atrium obtained during cardiac surgery from patients with (n = 6) and without (n = 6) atrial fibrillation (AF) were studied by microelectrode technique. For each preparation, ERP were measured at basic cycle lengths (BCL) of 1,600, 1,200, 800, and 400 msec in five different cells located around (0.8 mm) the stimulating electrode. Dispersion of ERP was significantly greater in the AF group (96.7 ± 9 versus 70.9 ± 9 msec, p = 0.01). In the non-AF group, we observed a positive linear correlation between (1) ERP and BCL (f = 0.86) (2) ADP₉₀ and BCL (= 0.93). On the contrary, in the AF group this correlation was absent between ERP and BCL (= 0.28), poor between ADP₉₀ and BCL (= 0.62). These results suggest that nonhomogeneous recovery of excitability (dispersion and poor adaptation) may be an important factor of arrhythmia. This inhomogeneity is present at the cellular level as well as in the entire heart.     

Performance of a Radiation Protection Cabin During Implantation of Pacemakers or Cardioverter Defibrillators

Radioprotection for Cardiac Device Implant . Introduction: Pacemaker implants are associated with a high cumulative exposure of the operators to radiation. Standard radiation protection with lead aprons is incomplete and the cause of spine disorders. A radiation protection cabin offers complete protection by surrounding the operator, without requiring a lead apron. Methods: We randomly and evenly assigned 60 patients undergoing implantations of permanent pacemakers or cardioverter defibrillators (ICD) with (a) a radiation protection cabin (cabin group, n = 30) versus (b) standard protection with a 0.5 mm lead‐equivalent apron (control group, n = 30). Radiation exposure was measured using personal electronic dosimeters placed on the thorax, back, and head of the operator. Results: The patient, procedural, and device characteristics of the 2 study groups were similar. All procedures in the cabin group were performed as planned without increase in duration or complication rate compared with the control group. The mean radiation dose to the head, normalized for fluoroscopy duration, was significantly lower in the cabin (0.040 ± 0.032 μSv/min) than in the control (1.138 ± 0.560 μSv/min) group (p < 0.0001). The radiation doses to the thorax (0.043 ± 0.027 vs 0.041 ± 0.040 μSv/min) and back (0.038 ± 0.029 vs 0.033 ± 0.018 μSv/min) in the cabin versus control group (under the apron) were similar. Conclusions: The use of a radiation protection cabin markedly decreased the exposure of the operator to radiation, and eliminated the need to wear a lead apron, without increasing the procedural time or complication rate during implantation of pacemaker and ICD. (J Cardiovasc Electrophysiol, Vol. 21, pp. 428–430, April 2010)     

Left Main Coronary Angioplasty: Assessment of a "Risk Score" to Predict Acute and Long-Term Outcome

Due to the recent emergence of adjunctive techniques such as cardiopulmonary bypass support, left main angioplasty may become more routinely applied in the near future. In order to choose the best possible therapy, a precise risk assessment will be desirable. Twenty-two left main angioplasties were thus reviewed and patients were divided in two groups according to a risk score adapted from a previously published jeopardy score. Group I included patients with a risk score ≤ 6 and group II patients with a risk score > 6. A cutoff criterion of six points was chosen because it represents the maximal amount of myocardium put at jeopardy from a single coronary stenosis. The success rate of the procedure was 77% and was similar in both groups. Of the 12 patients in group I, two patients underwent in-hospital bypass surgery and one of them died. Among the ten patients of group II, one sustained a myocardial infarction, three underwent acute surgery, and one patient died postoperatively. After a mean follow-up of 41 months, the total mortality rate was 17% in group I and 30% in group II. The long-term event-free survival rate was 75% in group I and 10% in group II (P = 0.004). The risk score was found to be a potentially important predictor of sustained success (long-term success: 4.4 ± 2.9 vs no long-term success: 8.3 ± 3.4; P = 0.01), although sophisticated statistical analysis was limited by the small number of patients. Thus, in patients with a low risk score, angioplasty seems to be an appropriate treatment while it appears that surgery should remain the standard therapy for patients with a calculated high risk score. However, the clinical significance of this new risk score remains to be determined with more elaborate statistical analysis applied to a larger number of patients.     

Methylation in positions 1 and 7 of angiotensin II A structure-activity relationship study

Six analogues of angiotensin II (Ang) were synthesized with modifications in positions 1 and 7. The study was undertaken in order to learn more about the influence of alkylations in positions 1 and 7 and their interdependence. Previous studies have shown that x,x-dimethylation of Gly (aminoisobutyric acid, Aib) in position 1 produces quite potent analogues, as does N-methylation of Gly (sarcosine). Combination of both C^x- and N^x-methylations to N-Me-Aib¹, however, did not produce an affinity increase. Decyclisation of the Pro⁷-residue produced moderately active analogues with position 7 N-methylation and inactive analogues if the N-alkylation was suppressed. In order to investigate a possible stereochemical interdependence of positions 1 and 7, a group of peptides with combinations of position 1 and 7 alkylations were investigated. The following analogues were prepared: [Sar¹, Aib⁷]Ang, [Sar¹,Aib⁷,Leu⁸]Ang, [Aib^1,7]Ang, [Aib^1,7, Leu⁸]Ang, [N-Me-Aib¹,Aib⁷]Ang, [N-Me-Aib¹,Aib⁷,Leu⁸]Ang. They were synthesized by classical solid phase synthesis using the BOC-TFA-HF scheme. The biological properties of these peptides were assessed on the rabbit aorta preparation and their binding potencies were measured on bovine adrenal membranes. Both on agonistic and antagonistic [Leu⁸]Ang analogues single Aib substitutions in position 1 or 7 induced affinity reduction in both bioassays. Simultaneous Aib modifications in positions 1 and 7 induced more important affinity loss in a synergic manner in both bioassays and as well for agonists and antagonists. The N-Me-Aib¹ modifications induce similar affinity loss with or without concomitant Aib⁷ modification. Agonistic (Phe⁸) analogues containing Aib in position 7 all have reduced intrinsic activity, indicating for the first time an influence of this position on the activation mechanism of the Ang receptor of the Type AT₁. © Munksgaard 1994.     

Electrocardiogram-Based Algorithm to Predict the Left Ventricular Lead Position in Recipients of Cardiac Resynchronization Systems

Introduction: Biventricular pacing is associated with various electrocardiographic patterns depending on the position of the left ventricular (LV) lead. We aimed to develop an electrocardiogram-based algorithm to predict the position of the LV lead.
Methods: The algorithm was developed in 100 consecutive recipients of cardiac resynchronization therapy (CRT) systems. QRS axis, morphology, and polarity were analyzed with a view to define the specific electrocardiographic characteristics associated with the various LV lead positions . The algorithm was prospectively validated in 50 consecutive CRT device recipients.
Results: The first analysis of the algorithm was the QRS morphology in V₁. A positive R wave in V₁ suggested LV lateral or posterior wall stimulation. A QS pattern was specific of anterior LV leads. In the presence of an R wave in V₁, V₆ was analyzed to distinguish between an inferior and anterior LV lead. Inferior leads were never associated with a positive V₆. To differentiate between lateral and posterior positions, we analyzed the pattern in V₂. Lateral leads were associated with an R morphology in V₁ and a negative V₂. Posterior leads were associated with an R morphology in V₁ and V₂. The algorithm allowed a reliable distinction between an inferior or anterior and a lateral or posterior lead position in 90% of patients. Inferior, anterior, lateral, and posterior positions were reliably distinguished in 80% of patients.
Conclusion: This algorithm predicted the position of the LV lead with a high sensitivity and predictive value.     

Reliability and Reproducibility of QRS Duration in the Selection of Candidates for Cardiac Resynchronization Therapy

Reliability and Reproducibility of QRS Duration . Background: A QRS >120 ms remains the recommended criterion for the selection of cardiac resynchronization therapy (CRT) candidates. However, the reproducibility of this measurement has not been studied thoroughly. Methods: QRS duration was measured by 3 experienced cardiologists and by automatic measurement on 228 electrocardiograms (ECGs) randomly collected from 188 subjects, including neonates, healthy adults, patients with complete and incomplete bundle branch block, and CRT candidates. All ECGs were recorded at a 25 mm/s sweep speed. Forty recordings were duplicated and 50 ECGs were recorded at both 25 and 50 mm/s. Results: Significant interobserver differences (P < 0.001) were found between each combination of paired observers, with an up to 50‐ms absolute variability between cardiologists and low concordance with computerized measurements. Intraobserver absolute variability was also significant (P < 0.01) for the 3 observers. These significant differences persisted (P < 0.01) when focusing our interest on the ECGs in the 100–140 ms range (defined as at least one out of the 4 measures in this range). Considering the 120 ms limit, 22 (27.5%) ECGs were differently classified by at least one of the cardiologists. We observed similar interobserver differences between each combination of paired observers with a 50 mm/s sweep speed. Conclusion: Manual QRS duration measurements were associated with significant inter‐ and intraobserver variability and low concordance with computerized measurements. The measurement of QRS is, therefore, operator‐dependent and a reevaluation of the measurement methods may be essential to develop clinical and investigative standards. (J Cardiovasc Electrophysiol, Vol. 21, pp. 890‐892, August 2010)     

The Anatomic Impact of Sequential,Additional, Ostial Radiofrequency Ablation Following Pulmonary Vein Cryo‐Isolation

Background : Although pulmonary vein (PV) stenosis is a serious complication of radiofrequency PV isolation, the anatomical impact of a combination of two energy sources on PV diameter has not been evaluated. The aim of this study was to evaluate the impact of supplementary point‐by‐point radiofrequency applications (following PV cryoablation) on the PV orifice diameter. Methods : Forty‐nine patients having undergone PV isolation for drug‐refractory atrial fibrillation were included. All had undergone cardiac computed tomography before ablation and again at least 3 months afterwards. When isolation with the cryoballoon was not complete, a conventional irrigated‐tip radiofrequency catheter was used for point‐by‐point applications. Results : Of the 189 target PVs, 117 were isolated with cryotherapy alone (cryo PVs) and 72 required additional radiofrequency (hybrid PVs). The second scan (performed an average of 11.4 ± 5.4 months after) showed a decrease in diameter for all the hybrid PVs (17.2 ± 2.6 to 16.3 ± 3.4 mm; P = 0.037) but no change for the cryo PVs. This change was associated with a decrease in left superior pulmonary vein (LSPV) diameter (19.2 ± 3.0 to 17.8 ± 4.9 mm, P = 0.014). There were no changes in other veins. A subgroup analysis for the LSPV revealed a decrease for the hybrid PVs (18.8 ± 3.6 to 15.9 ± 7.1 mm, P = 0.046) but not for the cryo PVs. Significant PV stenosis was observed in three hybrid PVs (two severe stenosis of the LSPV and one moderate stenosis of the right inferior pulmonary vein) but not in cryo PVs (4.1% vs 0%, respectively; P = 0.023). Conclusions : Cryoballoon ablation of the PV with adjunct, focal, irrigated ostial RF applications may be associated with a higher risk of PV stenosis. (PACE 2012;35:1420–1427)     

Pacemaker‐Mediated Tachycardia: Manufacturer Specifics and Spectrum of Cases

Pacemaker‐mediated tachycardia (PMT) is the term used to describe a repetitive sequence of sensed retrograde P waves followed by ventricular pacing at or below the maximum tracking rate. The following events can promote atrioventricular (AV) dissociation, retrograde conduction, and the onset of PMT: ventricular or atrial extrasystole, an excessively long programmed AV delay, external interference or myopotentials sensed by the atrial channel, atrial sensing or pacing failure, the absence of postventricular atrial refractory period extension after removal of a magnet, and VDD pacing at a higher rate than sinus rate. In contemporary devices, each manufacturer has a proprietary algorithm to detect and terminate PMT. Because of the increase in the number and complexity of the pacing algorithms and because of manufacturer‐driven differences, a basic understanding of these new algorithms is important for patient care. We review here the main elements of the physiopathology of this type of tachycardia, describe the specific characteristics of the different manufacturers, and present representative clinical cases.     

Optical Mapping Technique Applied to Biventricular Pacing:

GARRIGUE, S., et al .: Optical Mapping Technique Applied to Biventricular Pacing: Potential Mechanisms of Ventricular Arrhythmias Occurrence. Although it has been suggested that multisite ventricular pacing alleviates heart failure by restoring ventricular electrical synchronization, the respective roles of voltage output, interventricular delay, and pacing sites in the development of ventricular arrhythmias occurrence have not been studied during biventricular pacing or LV pacing. Voltage-sensitive dye was used in eight ischemic Langerdorff-perfused guinea pig hearts to measure ventricular activation times and examine conduction patterns during multisite pacing from three RV and four LV sites. The hearts were stained with di-4-ANEPPS and mapped with a   16 × 16   photodiode array at a resolution of 625 μm per diode. Isochronal maps of RV and LV activation were plotted. Ischemia was produced by gradually halving the perfusion output over 5 minutes. Pacing the RV apex and the base of the LV anterior wall was associated with the most homogeneous and rapid activation pattern (   28 ± 9   vs   41 ± 12   ms with the other configurations, P < 0.01), and no inducible arrhythmia. In six hearts, ventricular tachycardia could be induced when pacing from the right and left free walls with 20 ms of interventricular delay, at six times the pacing threshold output. In four hearts, simultaneous RV and LV pacing at high voltage output induced ventricular fibrillation with complex three-dimensional propagation patterns, independently of the pacing sites. During biventricular pacing with ischemia, pacing at high voltage output with a long interventricular delay is likely to induce ventricular arrhythmias, particularly when left and right pacing results in a conduction pattern orthogonal to the ventricular myocardial fibers orientation. PACE 2003; 26[Pt. II]:197–205)