Monophasic action potentials of the right atrium in patients with paroxysmal atrial fibrillation

Comprehensive evaluation of electrophysiological and 3D structural features of human atrial myocardium with insights on atrial fibrillation maintenance mechanisms

Atrial fibrillation (AF) occurrence and maintenance is associated with progressive remodeling of electrophysiological (repolarization and conduction) and 3D structural (fibrosis, fiber orientations, and wall thickness) features of the human atria. Significant diversity in AF etiology leads to heterogeneous arrhythmogenic electrophysiological and structural substrates within the 3D structure of the human atria. Since current clinical methods have yet to fully resolve the patient-specific arrhythmogenic substrates, mechanism-based AF treatments remain underdeveloped. Here, we review current knowledge from in-vivo, ex-vivo, and in-vitro human heart studies, and discuss how these studies may provide new insights on the synergy of atrial electrophysiological and 3D structural features in AF maintenance. In-vitro studies on surgically acquired human atrial samples provide a great opportunity to study a wide spectrum of AF pathology, including functional changes in single-cell action potentials, ion channels, and gene/protein expression. However, limited size of the samples prevents evaluation of heterogeneous AF substrates and reentrant mechanisms. In contrast, coronary-perfused ex-vivo human hearts can be studied with state-of-the-art functional and structural technologies, such as high-resolution near-infrared optical mapping and contrast-enhanced MRI. These imaging modalities can resolve atrial arrhythmogenic substrates and their role in reentrant mechanisms maintaining AF and validate clinical approaches. Nonetheless, longitudinal studies are not feasible in explanted human hearts. As no approach is perfect, we suggest that combining the strengths of direct human atrial studies with high fidelity approaches available in the laboratory and in realistic patient-specific computer models would elucidate deeper knowledge of AF mechanisms. We propose that a comprehensive translational pipeline from ex-vivo human heart studies to longitudinal clinically relevant AF animal studies and finally to clinical trials is necessary to identify patient-specific arrhythmogenic substrates and develop novel AF treatments.

Increased dispersion of atrial repolarization in Brugada syndrome

AIMS

Patients with Brugada syndrome (BS) often experience atrial fibrillation (AF) and atrial vulnerability, as measured by increased atrial conduction time. To date, however, dispersion of atrial repolarization has not been reported in these patients.

METHODS AND RESULTS

Monophasic action potentials (MAPs) recorded from four sites of the right atrium were analysed in 11 patients (10 men, 1 woman; mean age, 40 ± 9 years) with BS and in 10 controls (8 men, 2 women; mean age, 35 ± 8 years). None of these patients had a history of AF. Monophasic action potentials were recorded during right atrial pacing at a drive cycle length of 600 ms after continuous pacing. Dispersion of MAP duration (D-MAPD90) was defined as the difference between the maximum and minimum MAP duration measured at 90% repolarization (MAPD90). Inducibility of AF and repetitive atrial firing were also determined. The MAPD90 did not differ significantly between the BS and control groups (245 ± 42 vs. 228 ± 24 ms, P = ns), but D-MAPD90 was significantly higher in the BS group (69.1 ± 35.0 vs. 41.4 ± 10.3 ms, P < 0.05). Atrial fibrillation was induced in six BS patients and repetitive atrial firing in four, but neither was induced in any of the control subjects.

CONCLUSION

The significantly increased dispersion of MAPD90 observed in patients with BS suggests that the heterogeneity of atrial repolarization may contribute to the development of atrial fibrillation in patients with BS.

Global dispersion of right atrial repolarization in healthy pigs and patients

OBJECTIVE

To investigate the feasibility of monophasic action potential (MAP) mapping using an electroanatomical mapping system (CARTO) in obtaining information on global dispersion of atrial repolarization and to evaluate the role of dispersion of repolarization in the genesis of paroxysmal atrial fibrillation (PAF).

METHODS AND RESULTS

Right atrial MAPs were recorded from 53 +/- 18 sites in 10 healthy pigs and 33 +/- 21 sites in 6 patients with and 4 patients without history of PAF. In pigs, the global dispersions of activation time (AT), MAP duration and end of repolarization time (EOR), 70 +/- 8, 95 +/- 18 and 121 +/- 28 ms, respectively, were significantly greater than those among 10, 20 and 30 sites. In patients with PAF, the global dispersions of MAP duration and EOR (128 +/- 10 and 149 +/- 31 ms) were significantly greater than those in patients without PAF (84 +/- 10 and 91 +/- 17 ms).

CONCLUSION

MAP mapping using the CARTO system was feasible in experimental and clinical settings in obtaining information on global dispersion of atrial repolarization. The number of recording sites could significantly affect repolarization parameters. The dispersions of atrial repolarization were significantly greater in patients with PAF than those without, suggesting the involvement of an increased dispersion of repolarization in the genesis of PAF.

Differences in the aging-associated trends of the monophasic action potential duration and effective refractory period of the right and left atria of the rat

BACKGROUND

The incidence of atrial fibrillation (AF) increases with aging, but the aging-associated electrophysiological changes of atrial myocardium are poorly understood.

METHODS AND RESULTS

Based on the hypothesis that aging of the atrium enhances AF susceptibility, 30 Wistar rats were divided into 3 age groups: adult, middle-aged, and aged (n=20 per group). Their hearts were isolated and perfused by Langendorff apparatus. Monophasic action potential duration at 90% repolarization (MAPD(90)) and effective refractory period (ERP) at the basic stimulation cycle length (BCL: 400 ms), and MAPD(90) at other different stimulation cycle lengths in each age group were measured. At the BCL, the MAPD (90) of the right atrial myocardium was prolonged from the adult to the aged group, that of the left atrial myocardium was prolonged from the adult to middle-aged group, and the MAPD(90) of the left atrial myocardium in the aged group were shorter than that in the adult and middle-aged groups. The ERP of the atrial myocardium showed the same age-associated trend as MAPD(90). As the stimulation frequency increased, the MAPD(90) of both the left and right atrial myocardium shortened correspondingly in the adult and middle-aged groups, but in the aged group the MAPD(90) of the right atrial myocardium shortened markedly more than that of the left atrial myocardium.

CONCLUSIONS

There are different aging-associated electrophysiological changes in the right and left atrium, and the older heart is more vulnerable to developing the substrate for AF.

Monophasic action potential duration at the crista terminalis in patients with sinus node disease

BACKGROUND

The repolarization properties of the crista terminalis (CT) cells have not been elucidated in patients with sinus node disease (SND). In the present study a new technique of recording the monophasic action potential (MAP) at the CT was used to examine the repolarization of the right atrium (RA) in SND patients.

METHODS AND RESULTS

Symptomatic SND (n=13) patients and age-, sex-matched control patients (n=13) were tested. The MAP duration (MAPD) at a basic cycle length of 600 ms was recorded at the CT in the superior vena cava - RA junction and at the middle - anterior RA with the effective refractory period (ERP) at the high RA. In 6 controls and 4 SND patients, the effect of adenosine triphosphate on the MAPD was examined. The MAPD at the CT exceeded that at the middle - anterior RA in both groups. The MAPD at the CT in the SND group was significantly prolonged compared with the control group (CT: 358+/-39 ms vs 289+/-43 ms). Between the SND and control groups, the MAPD at the middle - anterior RA (278+/-36 ms vs 265+/-39 ms) and ERP (294+/-42 ms vs 266+/-41 ms) did not differ. Both the corrected-sinus node recovery time and sinoatrial conduction time were better correlated with the MAPD at the CT than the MAPD at the middle - anterior RA and ERP. Adenosine triphosphate shortened the MAPD, which was augmented at the CT in the SND patients.

CONCLUSION

A novel method of estimating the MAP at the CT revealed the characteristics of atrial repolarization in SND patients.

Rate-dependent changes in atrial action potential duration after short- duration rapid atrial pacing in humans

The effect of rapid atrial pacing on the rate adaptation of the atrial action potential duration was studied in humans. The right atrial monophasic action potential (RAMAP) of 5 patients was recorded before and after 30 min of rapid atrial pacing. The pacing cycle length (CL) was 146 +/- 9 ms, the shortest duration at which 1:1 capture was possible. The RAMAP duration at 90% repolarization (RMAPD) was measured. CL-dependent changes in RAMAPD (CL 600 ms-CL 300 ms) before and after rapid atrial pacing were 51.8 +/- 10.7 ms and 30.8 +/- 7.6 ms (p < 0.05), respectively.