Methods and Results— Among 32 family members, 5 were initially diagnosed with atrioventricular block after age 30; 4 were studied, 3 of whom later developed dilated cardiomyopathy. We found a heterozygous single-nucleotide mutation resulting in an amino acid substitution (A1180V) in all studied patients and in 6 other younger unaffected members but not in 200 control chromosomes. When expressed with the β1 subunit, the mutated channels exhibited a –4.5-mV shift of inactivation with slower recovery leading to a rate-dependent Na⁺ current reduction and a moderate increase in late Na⁺ current. Clinical study revealed that although QRS duration decreased with increasing heart rate in noncarrier family members, this change was blunted in unaffected carriers whose ECG and heart function were normal. Resting corrected QT interval of unaffected carriers was significantly longer than that of noncarriers, even though it was still within the normal range.

Conclusions— A1180V expresses a mild Na⁺ channel phenotype in vitro and a corresponding clinical phenotype in unaffected mutation carriers, implying that A1180V caused structural heart disease in affected carriers by disturbing Na⁺ influx and, hence, cellular Na⁺ homeostasis. The high penetrance of A1180V suggests this phenotype as a high risk factor for dilated cardiomyopathy with preceding atrioventricular block.

Methods and Results— CHF was induced in dogs by ventricular tachypacing (240 bpm x2 weeks). Cellular Ca²⁺-handling properties and expression/phosphorylation status of key Ca²⁺ handling and myofilament proteins were assessed in control and CHF atria. CHF decreased cell shortening but increased left atrial diastolic intracellular Ca²⁺ concentration ([Ca²⁺]_i), [Ca²⁺]_i transient amplitude, and sarcoplasmic reticulum (SR) Ca²⁺ load (caffeine-induced [Ca²⁺]_i release). SR Ca²⁺ overload was associated with spontaneous Ca²⁺ transient events and triggered ectopic activity, which was suppressed by the inhibition of SR Ca²⁺ release (ryanodine) or Na⁺/Ca²⁺ exchange. Mechanisms underlying abnormal SR Ca²⁺ handling were then studied. CHF increased atrial action potential duration and action potential voltage clamp showed that CHF-like action potentials enhance Ca²⁺_i loading. CHF increased calmodulin-dependent protein kinase II phosphorylation of phospholamban by 120%, potentially enhancing SR Ca²⁺ uptake by reducing phospholamban inhibition of SR Ca²⁺ ATPase, but it did not affect phosphorylation of SR Ca²⁺-release channels (RyR2). Total RyR2 and calsequestrin (main SR Ca²⁺-binding protein) expression were significantly reduced, by 65% and 15%, potentially contributing to SR dysfunction. CHF decreased expression of total and protein kinase A–phosphorylated myosin-binding protein C (a key contractile filament regulator) by 27% and 74%, potentially accounting for decreased contractility despite increased Ca²⁺ transients. Complex phosphorylation changes were explained by enhanced calmodulin-dependent protein kinase II expression and function and type-1 protein-phosphatase activity but downregulated regulatory protein kinase A subunits.

Conclusions— CHF causes profound changes in Ca²⁺-handling and -regulatory proteins that produce atrial fibrillation–promoting atrial cardiomyocyte Ca²⁺-handling abnormalities, arrhythmogenic triggered activity, and contractile dysfunction.

Methods and Results— We examined sympathetic nervous system responses to head-up tilt by combining NE plasma kinetics measurements and muscle sympathetic nerve activity recordings and by quantifying NET protein content in peripheral sympathetic nerves in patients with POTS compared with that in controls. POTS patients had an elevated heart rate during supine rest (81±2 bpm versus 66±2 bpm in healthy subjects [HS], P<0.01). Head-up tilt to 40° induced a greater rise in heart rate in patients with POTS (+24±4 bpm versus +13±2 bpm in HS, P<0.001). During rest in the supine position, muscle sympathetic nerve activity, arterial NE concentration, and whole-body NE spillover to plasma were similar in both groups. Muscle sympathetic nerve activity response to head-up tilt was greater in the POTS group (+29±3 bursts/min in patients with POTS and +13±2 bursts/min in HS, P<0.001), but the NE spillover rise was similar in both groups (51% in the POTS subjects and 50% in the HS). Western blot analysis of NET protein extracted from forearm vein biopsies in patients with POTS and HS demonstrated a decrease in the expression of NET protein in patients with POTS.

Conclusion— Patients with POTS exhibit a decrease in NET protein in their peripheral sympathetic nerves. Paradoxically, whole-body NE spillover to plasma during rest in the supine position and in response to head-up tilt is not altered despite excessive nerve firing rate in response to the head-up tilt.

Methods and Results— Twelve dogs underwent evaluation using a newly developed Carto-based 3D ultrasound system. After fiducial clip markers were percutaneously implanted at critical locations in each cardiac chamber, 3D ultrasound geometries, derived from a family of 2D intracardiac echocardiographic images, were constructed. Point-source error of 3D ultrasound-derived geometries, assessed by actual real-time 2D intracardiac echocardiographic clip sites, was 2.1±1.1 mm for atrial and 2.4±1.2 mm for ventricular sites. These errors were significantly less than the variance on CartoMerge computed tomographic images (atria: 3.3±1.6 mm; ventricles: 4.8±2.0 mm; P<0.001 for both). Target ablation at each clip, guided only by 3D ultrasound-derived geometry, resulted in lesions within 1.1±1.1 mm of the actual clips. Pulmonary vein ablation guided by 3D ultrasound-derived geometry resulted in circumferential ablative lesions. Mapping in 15 patients produced modestly smaller 3D ultrasound versus electroanatomic map left atrial volumes (98±24 cm³ versus 109±25 cm³, P<0.05). Three-dimensional ultrasound-guided pulmonary vein isolation and linear ablation in these patients were successfully performed with confirmation of pulmonary vein entrance/exit block.

Conclusions— These data demonstrate that 3D ultrasound images seamlessly yield anatomically accurate chamber geometries. Image volumes from the ultrasound system are more accurate than possible with CartoMerge computed tomographic imaging. This clinical study also demonstrates the initial feasibility of this guidance system for ablation in patients with atrial fibrillation.

Methods and Results— The first 100 consecutive patients (58.8±11.2 years old, 80 male) who underwent single-ring isolation for atrial fibrillation (66 intermittent, 18 persistent, 16 long-standing persistent) were followed up for 9.1±4.5 months. Recurrences were diagnosed by clinical symptoms and Holter monitoring. Patients with recurrences of sustained atrial arrhythmia >3 months after the procedure were offered a repeat procedure and were studied to determine the mechanisms of recurrence. Forty-six patients (46%) experienced sustained postprocedural atrial arrhythmias (35 had atrial fibrillation, and 34 had atrial flutter). Of these, 34 required a second procedure 7.0±3.1 months after their initial procedure. Reconnection of the posterior left atrium was seen in all patients with atrial fibrillation. Atrial flutter was most commonly due to mitral isthmus-dependent macroreentry (n=8, cycle length 368±116 ms) or macroreentry through 2 gaps in the ring of lesions (n=6, cycle length 328±115 ms). Posterior left atrium reisolation was achieved at the second procedure in all patients. Atrial flutter was successfully ablated and rendered noninducible in all patients. Six months after their last procedure, the Kaplan-Meier estimate of freedom from recurrence for all 100 patients was 81±5%.

Conclusions— Atrial fibrillation and atrial flutter recurrence is common after single-ring isolation. Reconnection of the posterior left atrium and macroreentry are the common mechanisms. Repeat ablation results in satisfactory short-term outcomes.