Stochastic spontaneous calcium release events and sodium channelopathies promote ventricular arrhythmias

Premature ventricular complexes (PVCs), the first initiating beats of a variety of cardiac arrhythmias, have been associated with spontaneous calcium release (SCR) events at the cell level. However, the mechanisms underlying the degeneration of such PVCs into arrhythmias are not fully understood. The objective of this study was to investigate the conditions under which SCR-mediated PVCs can lead to ventricular arrhythmias. In particular, we sought to determine whether sodium (Na⁺) current loss-of-function in the structurally normal ventricles provides a substrate for unidirectional conduction block and reentry initiated by SCR-mediated PVCs. To achieve this goal, a stochastic model of SCR was incorporated into an anatomically accurate compute model of the rabbit ventricles with the His-Purkinje system (HPS). Simulations with reduced Na⁺ current due to a negative-shift in the steady-state channel inactivation showed that SCR-mediated delayed afterdepolarizations led to PVC formation in the HPS, where the electrotonic load was lower, conduction block, and reentry in the 3D myocardium. Moreover, arrhythmia initiation was only possible when intrinsic electrophysiological heterogeneity in action potential within the ventricles was present. In conclusion, while benign in healthy individuals SCR-mediated PVCs can lead to life-threatening ventricular arrhythmias when combined with Na⁺ channelopathies.

JPH-2 interacts with Cai-handling proteins and ion channels in dyads: Contribution to premature ventricular contraction-induced cardiomyopathy

BACKGROUND

In a canine model of premature ventricular contraction-induced cardiomyopathy (PVC-CM), Cav1.2 is downregulated and misplaced from transverse tubules (T tubules). Junctophilin-2 (JPH-2) is also downregulated.

OBJECTIVES

The objectives of this study were to understand the role of JPH-2 in PVC-CM and to probe changes in other proteins involved in dyad structure and function.

METHODS

We quantify T-tubule contents (di-8-ANEPPS fluorescence in live myocytes), examine myocyte ultrastructures (electron microscopy), probe JPH-2-interacting proteins (co-immunoprecipitation), quantify dyad and nondyad protein levels (immunoblotting), and examine subcellular distributions of dyad proteins (immunofluorescence/confocal microscopy). We also test direct JPH-2 modulation of channel function (vs indirect modulation through dyad formation) using heterologous expression.

RESULTS

PVC myocytes have reduced T-tubule contents but otherwise normal ultrastructures. Among 19 proteins examined, only JPH-2, bridging integrator-1 (BIN-1), and Cav1.2 are highly downregulated in PVC hearts. However, statistical analysis indicates a general reduction in dyad protein levels when JPH-2 is downregulated. Furthermore, several dyad proteins, including Na/Ca exchanger, are missing or shifted from dyads to the peripheral surface in PVC myocytes. JPH-2 directly or indirectly interacts with Cai-handling proteins, Cav1.2 and KCNQ1, although not BIN-1 or other scaffolding proteins tested. Expression in mammalian cells that do not have dyads confirms direct JPH-2 modulation of the L-type Ca channel current (Cav1.2/voltage-gated Ca channel β subunit 2) and slow delayed rectifier current (KCNQ1/KCNE1).

CONCLUSION

JPH-2 is more than a "dyad glue": it can modulate Cai handling and ion channel function in the dyad region. Downregulation of JPH-2, BIN-1, and Cav1.2 plays a deterministic role in PVC-CM. Dissecting the hierarchical relationship among the three is necessary for the design of therapeutic interventions to prevent the progression of PVC-CM.

Sodium current reduction unmasks a structure-dependent substrate for arrhythmogenesis in the normal ventricles

Background

Organ-scale arrhythmogenic consequences of source-sink mismatch caused by impaired excitability remain unknown, hindering the understanding of pathophysiology in disease states like Brugada syndrome and ischemia.

Objective

We sought to determine whether sodium current (I_Na) reduction in the structurally normal heart unmasks a regionally heterogeneous substrate for the induction of sustained arrhythmia by premature ventricular contractions (PVCs).

Methods

We conducted simulations in rabbit ventricular computer models with 930 unique combinations of PVC location (10 sites) and coupling interval (250–400 ms), I_Na reduction (30 or 40% of normal levels), and post-PVC sinus rhythm (arrested or persistent). Geometric characteristics and source-sink mismatch were quantitatively analyzed by calculating ventricular wall thickness and a newly formulated 3D safety factor (SF), respectively.

Results

Reducing I_Na to 30% of its normal level created a substrate for sustained arrhythmia induction by establishing large regions of critical source-sink mismatch (SF<1) for ectopic wavefronts propagating from thin to thick tissue. In the same simulations but with 40% of normal I_Na, PVCs did not induce reentry because the volume of tissue with SF<1 was >95% smaller. Likewise, when post-PVC sinus activations were persistent instead of arrested, no ectopic excitations initiated sustained reentry because sinus activation breakthroughs engulfed the excitable gap.

Conclusion

Our new SF formulation can quantify ectopic wavefront propagation robustness in geometrically complex 3D tissue with impaired excitability. This novel methodology was applied to show that I_Na reduction precipitates source-sink mismatch, creating a potent substrate for sustained arrhythmia induction by PVCs originating near regions of ventricular wall expansion, such as the RV outflow tract.

[Preferential conduction to right ventricular outflow track leads to left bundle-branch block morphology in patient with premature ventricular contraction originating from the aortic sinus cusp]

OBJECTIVE

The purpose of this study was to explore the relationship between originate and breakout and radiofrequency catheter ablation strategy in patients undergoing radiofrequency ablation for premature ventricular contractions originating from the aortic sinus cusp (ASC) using 3-dimensional electro anatomic mapping.

METHODS

This study included 21 consecutive patients (10 male) underwent ablation for frequent PVCs originating from ASC in our hospital between May 2009 and February 2012. Electro anatomic mapping and ablation of right ventricular outflow track (RVOT) and left ventricular outflow track (LVOT) were performed with the 7F 4-mm-tip ablation catheter from right femoral vein and artery. Activation mapping and pacing mapping were performed in all patients.

RESULTS

Ablation was successful in all 21 patients successful ablation target in left coronary sinus cusp (LCC, n = 17), in right coronary sinus cusp (RCC, n = 2) and in noncoronary sinus cusp (NCC, n = 2). Seven patients showed a RBBB morphology (group A) and 14 patients showed a LBBB morphology (group B). In group A, earliest ventricular activation (EVA) was recorded 22 - 34 (27.4 ± 4.6) ms earlier before QRS at the site of catheter ablation in ASC. In group B, EVA was later in RVOT than that in ASC in 5 patients and EVA at the site of catheter ablation in RVOT and ASC was 22 - 28 (25.2 ± 2.7) ms and 26 - 40 (32.8 ± 5.2) ms, respectively (t = -3.6, P = 0.024) while EVA was earlier in the remaining 9 patients and EVA recorded in RVOT and ASC was 22 - 38 (28.7 ± 5.9) ms and 18 - 28 (22.7 ± 3.6) ms, respectively (t = 3.8, P = 0.005).

CONCLUSION

Patients with premature ventricular contractions originating from the ASC often show preferential conduction to the RVOT, which may explain the LBBB morphology of ECG in these patients.

Repolarization abnormalities in Duchenne-type muscular dystrophy

OBJECTIVES

Duchenne-type muscular dystrophy (DMD) is an X-linked recessive inherited disease affecting mainly the skeletal and cardiac muscles. We aimed to seek associations between the incidence of ventricular arrhythmias and corrected QT (QTc) dispersion and its component, corrected JT (JTc) dispersion in patients with DMD.

STUDY DESIGN

The study included 43 consecutive male patients (mean age 8.8+/-3.0 years; range 3 to 17 years) with DMD. On standard 12-lead electrocardiograms (ECG) the QT and JT intervals and the corrected QT (QTc) and JTc dispersions were calculated. Ventricular extrasystoles were assessed on 24-hour Holter ECG recordings. Ventricular dysrhythmic patterns were evaluated according to the Lown-Wolf classification. The results were compared with those of a control group of 34 healthy children (mean age 9.5+/-3.1 years).

RESULTS

The mean QTc and JTc dispersion values were significantly higher in DMD patients compared to controls (QTc: 78.0+/-20.6 msec vs. 50.9+/-16.5 msec; JTc: 77.6+/-20.5 msec vs. 50.8+/-17.7 msec; p<0.05). The results of Holter monitoring were evaluated in 36 patients and in 33 controls. Ventricular extrasystoles were found in six patients (16.7%) and in one (grade I) control subject (3%). The incidence of pathological findings was significantly higher in the study group (p<0.05), including grade I pathology in four patients, grade II pathology in one patient, and grade IV in one patient. QTc and JTc dispersion values of the patients with and without ventricular extrasystoles showed no statistically significant difference (p>0.05).

CONCLUSION

Similar QTc and JTc dispersion values detected in patients with and without ventricular extrasystoles may suggest that ventricular repolarization abnormalities occur in early life and may predispose to the development of ventricular arrhythmias in the long-term.

Modest Reductions of Cardiac Calsequestrin Increase Sarcoplasmic Reticulum Ca 2+ Leak Independent of Luminal Ca 2+ and Trigger Ventricular Arrhythmias in Mice

Cardiac calsequestrin–null mice ( Casq2 −/− ) display catecholaminergic ventricular tachycardia akin to humans with CASQ2 mutations. However, the specific contribution of Casq2 deficiency to the arrhythmia phenotype is difficult to assess because Casq2 −/− mice also show significant reductions in the sarcoplasmic reticulum (SR) proteins junctin and triadin-1 and increased SR volume. Furthermore, it remains unknown whether Casq2 regulates SR Ca 2+ release directly or indirectly by buffering SR luminal Ca 2+ . To address both questions, we examined heterozygous ( Casq2 +/− ) mice, which have a 25% reduction in Casq2 but no significant decrease in other SR proteins. Casq2 +/− mice (n=35) challenged with isoproterenol displayed 3-fold higher rates of ventricular ectopy than Casq2 +/+ mice (n=31; P <0.05). Programmed stimulation induced significantly more ventricular tachycardia in Casq2 +/− mice than in Casq2 +/+ mice. Field-stimulated Ca 2+ transients, cell shortening, L-type Ca 2+ current, and SR volume were not significantly different in Casq2 +/− and Casq2 +/+ myocytes. However, in the presence of isoproterenol, SR Ca 2+ leak was significantly increased in Casq2 +/− myocytes ( Casq2 +/− 0.18±0.02 F ratio versus Casq2 +/+ 0.11±0.01 F ratio , n=57, 60; P <0.01), resulting in a significantly higher rate of spontaneous SR Ca 2+ releases and triggered beats. SR luminal Ca 2+ measured using Mag-Fura-2 was not altered by Casq2 reduction. As a result, the relationship between SR Ca 2+ leak and SR luminal Ca 2+ was significantly different between Casq2 +/− and Casq2 +/+ myocytes ( P <0.01). Thus, even modest reductions in Casq2 increase SR Ca 2+ leak and cause ventricular tachycardia susceptibility under stress. The underlying mechanism is likely the direct regulation of SR Ca 2+ release channels by Casq2 rather than altered luminal Ca 2+ .

Rotigaptide (ZP123) prevents spontaneous ventricular arrhythmias and reduces infarct size during myocardial ischemia/reperfusion injury in open-chest dogs

The antiarrhythmic and cardioprotective effect of increasing gap junction intercellular communication during ischemia/reperfusion injury has not been studied. The antiarrhythmic peptide rotigaptide (previously ZP123), which maintains gap junction intercellular communication, was tested in dogs subjected to a 60-min coronary artery occlusion and 4 h of reperfusion. Rotigaptide was administered i.v. 10 min before reperfusion as a bolus + i.v. infusion at doses of 1 ng/kg bolus + 10 ng/kg/h infusion (n = 6), 10 ng/kg bolus + 100 ng/kg/h infusion (n = 5), 100 ng/kg bolus + 1000 ng/kg/h infusion (n = 8), 1000 ng/kg bolus + 10 mug/kg/h infusion (n = 6), and vehicle control (n = 5). Premature ventricular complexes (PVCs) were quantified during reperfusion. A series of four or more consecutive PVCs was defined as ventricular tachycardia (VT). The total incidence of VT was reduced significantly with the two highest doses of rotigaptide (20.3 +/- 10.9 and 4.3 +/- 4.1 events; p < 0.05) compared with controls (48.7 +/- 6.0). Total PVCs were reduced significantly from 25.1 +/- 4.2% in control animals to 11.0 +/- 4.4 and 1.7 +/- 1.3% after the two highest doses of rotigaptide. Infarct size, expressed as a percentage of the left ventricle, was reduced significantly from 13.2 +/- 1.9 in controls to 7.1 +/- 1.0 (p < 0.05) at the highest dose of rotigaptide. Ultrastructural evaluation revealed no differences in myocardial injury in the infarct area, area at risk, border zone, or normal zone in vehicle and rotigaptide-treated animals. However, rotigaptide did increase the presence of gap junctions in the area at risk (p = 0.022, Fisher's exact test). Rotigaptide had no effect on heart rate, blood pressure, heart rate-corrected QT interval, or left ventricular end-diastolic pressure. In conclusion, these results demonstrate that rotigaptide is a potent antiarrhythmic compound with cardioprotective effects and desirable safety.

Acute myocarditis mimicking acute myocardial infarction: a clinical nightmare with forensic implications

Authors present the case of the sudden death of a 30-year-old man, 3 h since his hospitalization by the onset of aspecific chest pain. ECG findings revealed the presence of localized ST segment elevation in precordial leads (V1-V4) and DII-DII, and aVF mimicking acute antero-inferior myocardial infarction. A diagnosis of acute antero-inferior myocardial infarction was advanced and the patient introduced to thrombolytic therapy. Suddenly, on ECG monitor, conduction abnormalities were early recorded (ventricular extrasystole) followed by ventricular tachycardia degenerating in fatal ventricular fibrillation. An alleged medical malpractice was sued against the cardiologist. A complete immunohistochemical study was performed. Histologically, the heart presented massive interstitial lymphocytic infiltrate and focal myocytes necrosis. The diagnosis of acute lymphocytic myocarditis was established as the cause of death.

Histological characterization of microlesions induced by myocardial contrast echocardiography

BACKGROUND

Myocardial contrast echocardiography (MCE) has been shown to have a potential for apparently reversible side effects related to the interaction of ultrasound with the contrast microbubbles, including premature ventricular contractions and microvascular leakage. We investigated the potential for high-dose MCE to induce histologically definable microlesions.

METHODS

Myocardial contrast echocardiography with 1:4 end-systolic triggering was performed at 1.5 MHz and 1.7 mechanical index in a short axis view of the left ventricle in rats. Two high doses (500 microl/kg) of Optison agent were given 5 minutes apart during 10 minutes of echocardiography. For histology, the hearts were perfused and fixed in 10% neutral-buffered formalin. Slides from rats sacrificed 1 day after MCE were scored blind by a pathologist, and, in addition, photomicrographs in the anterior half were evaluated by digital image analysis.

RESULTS

In rats sacrificed 10 minutes after MCE, microvascular leakage and petechiae were highly significant. However, lesions displaying necrotic debris associated with inflammatory infiltrates were not histologically evident at this time. Heart samples 24 hours after MCE showed microlesions with inflammatory infiltrates scattered primarily over the anterior half of the sections. Pathologically, there was inflammatory cell infiltration in areas of 0.6 +/- 0.5% for shams and 3.6 +/- 3.6% for MCE (P < 0.01). Analysis of photographs from the anterior wall found microlesion areas of 0.5 +/- 0.8% for shams and 7.4 +/- 5.0% for MCE (P < 0.02). For rats sacrificed 1 week and 6 weeks after MCE, the microlesions healed to form small fibrous regions interspersed with normal myocytes.

CONCLUSION

High-dose MCE has a potential for causing microscale lesions in the myocardium and the possibility of therapeutic applications.

The relationship of resting S-T segment depression to the severity of subvalvular aortic stenosis and the presence of ventricular premature complexes in the dog

Electrocardiograms (ECG) from 35 dogs with subvalvular aortic stenosis (SAS) with a left ventricular outflow tract pressure gradient (PG) of > or =50 mm Hg were retrospectively evaluated for S-T segment depression (STD, > or =0.2 mV in lead II). Pressure gradient, age, heart rate (HR), and number of ventricular premature complexes (VPCs) on a 24-hour ambulatory ECG for dogs with STD were not significantly different from those for dogs without STD. The S-T segment deviation did not correlate significantly with PG, age, HR, or VPCs. The significance of STD in the dog with SAS remains uncertain. Long-term prospective studies are needed to fully understand this observation.

Association of ventricular premature complexes with electrocardiographic-estimated left ventricular mass in a population of African-American and white men and women (The Atherosclerosis Risk in Communities

Increased left ventricular (LV) mass is often found in adults and is a powerful predictor of cardiovascular mortality. To test the hypothesis that an electrocardiographic estimate of LV mass--the Cornell voltage--is associated with ventricular premature complexes (VPCs) in free-living adults, a cross-sectional analysis of the predictors of VPCs on a 2-minute rhythm strip in a population-based sample of 13,606 middle-aged, African-American and white men and women from 4 US communities in the Atherosclerosis Risk in Communities Study baseline examinations was performed. In adults without known coronary artery disease, the prevalence of VPCs increases monotonically with increasd Cornell voltages within ethnicity and gender groups. Independent of systemic hypertension, serum electrolytes, age, heart rate, educational attainment, gender, and ethnicity, a millivolt increase in Cornell voltage was associated with a 20% to 30% increase in the prevalence odds ratio of VPCs on the 2-minute electrocardiogram. Thus, Cornell voltage is associated with VPCs on a 2-minute electrocardiogram. The association is consistent in African-Americans, whites, men, and women.

Hydroxychloroquine overdose: toxicokinetics and management

BACKGROUND

The management and toxicokinetics of hydroxychloroquine overdose are poorly described.

CASE REPORT

We report a case of an 18-year-old girl who ingested 20 g of hydroxychloroquine. She developed marked hypokalemia, hypotension, and ventricular tachyarrhythmias but survived with treatment including intubation, adrenaline infusion, high-dose diazepam, and aggressive potassium replacement. Plasma hydroxychloroquine level was 29.40 mumol/L (9.87 mg/L) 2 hours after ingestion and the elimination half-life of hydroxychloroquine was 22 hours.

CONCLUSIONS

The clinical manifestations of this hydroxychloroquine overdose were similar to those reported for chloroquine overdose and the management principles recommended for chloroquine overdose appeared to be efficacious in this case.

Localization of precise origin of idiopathic ventricular tachycardia from the right ventricular outflow tract by a 12-lead ECG: a study of pace mapping using a multielectrode "basket" catheter

Radiofrequency catheter ablation guided by pace-mapping techniques has proven effective in eliminating idiopathic ventricular tachycardia (VT) originating from the right ventricular outflow tract (RVOT). A method for rapidly identifying the origin of VT from 12-lead electrocardiogram (ECG) findings would be helpful for the catheter ablation procedure. The purpose of this study is to precisely localize the origin of idiopathic VT from the RVOT by a 12-lead ECG from a study of multipoint pace mapping. In one patient with premature ventricular complex (PVC) and 3 with VT, a "basket" catheter was deployed in the RVOT for bipolar pacing from 56 sites in the endocardium of RVOT. Under fluoroscopy the pacing sites were classified into the septum and free wall. We investigated the QRS morphology in leads, I, II, and III; the depth of the QS wave in leads aVR and aVL; and the height of the initial r wave in leads V1 and V2. Pacing was captured in 30-47 of 56 sites (54%-84%). As the pacing sites changed from the anterior to posterior of the septum, the QS notch (-) type in lead I shifted through rs to R, while a shift from R type to rR' or Rr' was noted in leads II and III. As the pacing sites changed from the anterior to posterior of the free wall, lead I showed a shift from the QS notch (+) type to R, while a shift from rR' to Rr' (or rR' unchanged) was found in leads II and III. The depth of the QS wave in leads aVR and aVL showed a tendency for aVR to be deeper than aVL toward the posterolateral attachment of both the septum and free wall, whereas aVL tended to be deeper than aVR toward the anterior attachment. The initial r waves in V1 and V2 became greater as the pacing site was positioned at a higher or more posterior location. These findings may provide more precise and clinically useful diagnostic information on the site of the origin of idiopathic VT originating from the RVOT by a 12-lead ECG.

Reduction in QT dispersion and ventricular arrhythmias by ischaemic preconditioning in anaesthetized, normotensive and spontaneously hypertensive rats

QT dispersion is a marker for dispersion of ventricular repolarization and electrical instability of the heart. However, QT dispersion remains undocumented in both normotensive rats (NTRs) and spontaneously hypertensive rats (SHRs), in particular in conditions of myocardial ischaemia/reperfusion (isch./rep.) and ischaemic preconditioning (IP). Therefore, we assessed the effects of IP on the dynamic change of QT and QTc dispersion during isch./rep., and on isch.- and rep.-induced ventricular arrhythmias in both NTRs and SHRs. Isch. and rep. were produced by occlusion and release of a snare around the left coronary artery in all rats. The effect of IP (three cycles of 3 min coronary artery occlusion and 5 min rep.) on myocardial repolarization and on development of isch.- and rep.-induced ventricular arrhythmias was studied in 12 NTRs and 12 SHRs. Another 12 NTRs or 12 SHRs were subjected to 10 min of isch. followed by 10 min rep. without IP. SHRs have significantly longer QT- and QTc-intervals as well as QT and QTc dispersion before isch. compared to NTRs. Myocardial isch. and early rep. largely increased QT and QTc dispersion in both NTRs and SHRs and resulted in a high incidence of isch.- and rep.-induced ventricular tachycardia (VT) and fibrillation (VF). IP significantly reduced QT and QTc dispersion in SHRs before isch., and remarkably reduced the elevation of QT and QTc dispersion during a prolonged period of isch. and rep. in all rats. This protective effect on electrophysiology of IP was associated with an antiarrhythmic effect against both isch.- and rep.-induced ventricular arrhythmias in NTRs and SHRs. Our data indicate that: 1) SHRs have a significantly higher baseline dispersion of ventricular repolarization than NTRs; 2) IP provides protection against ventricular arrhythmias in SHRs; 3) the increasing QT dispersion provoked by myocardial isch. and rep. is associated with a high incidence of isch.- and rep.-induced ventricular arrhythmias and; 4) the reduction of QT dispersion by IP may be involved in its protective effect against isch.- and rep.-induced arrhythmias in both NTRs and SHRs.

Intraoperative arrhythmias and tissue damage during transmyocardial laser revascularization

BACKGROUND

Transmyocardial laser revascularization creates transmural channels to improve myocardial perfusion. Different laser sources and ablation modalities have been proposed for transmyocardial laser revascularization. We investigated the incidence of cardiac arrhythmias and laser-tissue interactions during transmyocardial laser revascularization of normal porcine myocardium with three different lasers.

METHODS

We used a continuous-wave, chopped CO2 laser (20 J/pulse, 15 ms/pulse) synchronized with the R wave; a holmium:yttrium aluminum garnet (Ho:YAG) laser (2 J/pulse, 250 micros/pulse, 5 Hz); and a xenon-chloride (excimer, Xe:Cl) laser (35 mJ/pulse, 20 ns/pulse, 30 Hz). Each laser was used 30 times as the sole modality in four consecutive pigs, yielding 120 channels.

RESULTS

The average number of pulses needed to create a channel was 1, 11 +/- 4, and 37 +/- 8 for the CO2, Ho:YAG, and Xe:Cl lasers, respectively. All Ho:YAG and Xe:Cl channels had premature ventricular contractions. Ventricular tachycardia occurred in 70% of the Xe:Cl and 60% of the Ho:YAG channels. Only 36% of the CO2 channels had premature ventricular contractions, and only 3% of the CO2 channels had ventricular tachycardia (p < 0.001 versus Ho:YAG and Xe:Cl). Ho:YAG channels were highly irregular: each had a 0.6-mm-wide central zone surrounded by a ring of coagulation necrosis (diameter, 1.84 +/- 0.67 mm) with effaced cellular architecture in a thin hemorrhagic zone. The Xe:Cl sections exhibited the same patterns on a smaller scale (diameter, 0.74 +/- 0.18 mm). The CO2 channels were straight and well demarcated. The zone of structural and thermal damage extended over half the channel's diameter, measuring 0.52 +/- 0.25 mm.

CONCLUSIONS

During transmyocardial laser revascularization, the CO2 laser synchronized with the R wave is significantly less arrhythmogenic than the Ho:YAG and Xe:Cl lasers not synchronized with the R wave. In addition, the interaction of the CO2 laser with porcine cardiac tissue is significantly less traumatic than that of the Ho:YAG and the Xe:Cl lasers.

Cardiac magnetic resonance imaging findings in patients with right ventricular outflow tract premature contractions

AIMS

To assess prospectively the value of cardiac magnetic resonance imaging in patients with apparently idiopathic premature contractions arising from the right ventricular outflow tract.

METHODS

We compared magnetic resonance imaging scans in 19 patients (13 males and six females, mean age 44 years) with frequent (> 100 per hour), monomorphic (left bundle branch block and inferior axis morphology) extrasystoles, and in 10 volunteers (four males and six females, mean age 36.7 years) without structural heart disease. Magnetic resonance imaging studies (1 or 1.5 Tesla) included spin-echo and gradient-echo sequences in the standard planes. The presence of structural and dynamic abnormalities of the right and left ventricles, such as reduced wall thickness, systolic bulging, and decreased systolic thickening, were evaluated. In addition, end-diastolic diameters of the right ventricular outflow tract were measured in the transverse plane.

RESULTS

The dimensions of the right ventricular outflow tract were wider in patients with extrasystoles compared to the control group. Mean anteroposterior and transverse diameters were 39.6 +/- 4.6 mm vs 29.9 +/- 4.8 mm (P < 0.01) and 27.5 +/- 3.8 mm vs 20.5 +/- 2.5 mm (P < 0.01), respectively. Wall motion and morphological abnormalities were present in 16/19 (84%) patients, and were confined to the anterolateral wall in 15/16 cases. All normal subjects had normal magnetic resonance imaging findings (P = 0.008).

CONCLUSIONS

Cardiac magnetic resonance imaging revealed that in patients with idiopathic right ventricular outflow tract premature contractions there was a higher rate of morphological and functional abnormalities of the right ventricular outflow tract than in the normal subjects. Large studies and long follow-up are needed to confirm whether these findings could help identify a localized form of arrhythmogenic cardiomyopathy, and its clinical significance.

Clinical meaning of ventricular ectopic beats in the diagnosis of HIV-related myocarditis: a retrospective analysis of Holter electrocardiographic recordings, echocardiographic parameters, histopathological and virologic findings

Clinical-pathological studies have demonstrated that in 46-51% of AIDS patients a lymphocytic interstitial myocarditis can be found at autopsy. In > 80% of these patients no specific etiologic factor for myocarditis was found. This pathological finding is believed to be related to a specific pathogenetic action of HIV on myocardial tissue and it is called HIV-related myocarditis (HRM). In 15-30% of patients with lymphocytic interstitial myocarditis ventricular arrhythmias have been described. In order to assess the prevalence and the predictive value of ventricular ectopic beats (VEB) in the diagnosis of HRM, we performed a retrospective analysis of 24-hour Holter recordings, M-mode and two-dimensional echocardiographic and Doppler parameters and post-mortem myocardial histopathological and virologic findings on a selected sample of 35 NYHA functional class II patients died of AIDS. The patients were divided into two groups according to post-mortem histopathological findings of myocardium specimens: Group 1 (n = 19) including patients with histopathological findings consistent with diagnosis of HRM; Group 2 (n = 16), including patients without histopathological findings of myocarditis. Group 2 patients represented the control group. The retrospective analysis demonstrated a greater prevalence of VEB class IV and subclass IVb in Group 1 compared to Group 2 (p = 0.009 and p = 0.004, respectively). The other classes of VEB did not present a statistically significant difference between groups. VEB class IV presented a 81.2% diagnostic predictive value (subclass IVa: 50%; subclass IVb: 90.9%). Ejection fraction, kinetic score and Doppler E/A ratio, Ei Area, Ai Area and Ai Area/total Area ratio and isovolumetric relaxation time were significantly correlated to Lown's classes of VEB (p < 0.001) and to the values of CD+ cells (p < 0.001); on the other hand, VEB classes correlated significantly with the values of CD+ cells (p < 0.001). Syncytial cells and HIV p24 antigen in cultured myocytes were detected in 17 Group 1 patients (89.4%) and in 2 Group 2 patients (12.5%; p < 0.001). These results have demonstrated that in selected cases of AIDS patients specific classes of VEB may represent a simple and sensitive electrocardiographic marker of HRM. VEB classes correlate significantly with systolic and diastolic echocardiographic parameters and to the values of CD4+ cells. Furthermore, in patients with HRM a direct pathogenetic action of HIV may be assumed.

[Experimental production of tricuspid valve and papillary muscle lesions by premature ventricular contractions due to ventricular stimulation in rabbits]

Ventricular bigeminy or trigeminy can spontaneously occur in anesthetized rabbits forced into the supine position. Premature ventricular contractions (PVCs) of this type are characterized by a long coupling time and superimposition of the following P waves. Rabbits with PVCs of this type frequently develop peculiar mitral complex lesions which are detected by deposition of colloidal carbon. This study examined the effects on the tricuspid complex of artificial PVCs induced by left ventricular pacing in rabbits. Anesthetized rabbits were forced into the supine position under electrocardiographic monitoring. The animals were divided into those with spontaneous PVCs, those with artificial PVCs, and those without PVCs as controls. Colloidal carbon (1 ml) was intravenously injected into the animals the next day. All animals were sacrificed after 1 week. Tricuspid complex lesions were found in 2.0% of animals with spontaneous PVCs, in 17.6% of those with artificial PVCs, and in none of the controls. These results indicate that artificial PVCs induced by left ventricular pacing can cause peculiar tricuspid complex lesions.

[Chronostructure of ectopic heart activity in the acute phase of myocardial infarction]

7-day monitoring of cardiac rhythm has been conducted in 42 patients with myocardial infarction (MI) and 15 patients with chronic ischemic heart disease. Hour-by-hour analysis of extrasystole demonstrates that probability of ventricular arrhythmia is maximal in transmural MI, the first 3 days of acute MI are most arrhythmogenic. Follow-up of ventricular ectopic activity (VEA) showed the latter to significantly enhance early in the morning, afternoon and on the first 5 days after midnight. In unpenetrating MI, VEA intensifies in the morning, afternoon and postmidnight hoars. Atrial ectopic activity (AEA) in transmural MI enhances early in the morning, afternoon and at night (on the first 3 days). AEA in unpenetrating MI is more intensive late in the morning and afternoon.

Anatomic substrate of the experimentally-created atrioventricular node re-entrant tachycardia in the dog

Despite major success in the treatment of atrioventricular (AV) node reentrant tachycardia using either catheter ablation or surgery, the morphologic basis underlying AV node reentry is not yet clear. A canine model of AV node reentrant tachycardia was used to examine the histologic features of the reentry circuit. AV node reentrant tachycardia was created in 4 of 8 dogs by a right atrial division which divided the right atrial free wall and the atrial septum into upper and lower portions on a plane between the mid-right atrial free wall and the fossa ovalis. The AV junctional area of all dogs were serially sectioned on a plane that was perpendicular to the AV annulus and the septum. The slices were stained with Masson's trichrome technique. The connections between atrial fibers and the compact AV node and the common AV bundle were examined, and comparison of the histologic features between dogs with and without AV nodal re-entry was made. The histologic examinations showed that, in all dogs, the operation scar was remote from the AV junctional area leaving the Koch's triangle intact. The compact node received its atrial inputs mainly from the anterosuperior and posterior aspects of the Koch's triangle. However, both atrial inputs gave off superficial (subendocardial) fibers that by-passed the compact node to terminate at the base of tricuspid valve. These superficial fibers might function as the proximal link between the dual AV nodal inputs by means of lateral connections. There was no bypass connection between atrial fibers and the common AV bundle. The histologic features of the AV junctional area was not different between dogs with and without AV nodal reentry. In conclusion, AV nodal reentry involves the anterior and posterior atrio-nodal inputs which function as dual AV nodal pathways, and the superficial bypass fibers form the proximal linkage between the two inputs. These structures, together with the compact node, complete the reentry circuit.

Methotrexate-linked ventricular arrhythmias

A 36-year-old male, who 1 year previously had survived a large anterior myocardial infarction, followed by cardiac arrest, was treated a few months for psoriasis with oral methotrexate, at single weekly oral doses of up to 10 mg, when he had to be hospitalized due to anginal pain and palpitation. Repeated 24-hour electrocardiogram recordings revealed ventricular ectopy up to 580 premature beats per hour. The ventricular premature beats were almost completely abolished after a few days' discontinuation of methotrexate therapy but recurred a few hours after an attempt to restart it had been made. A coronary angiogram showed only minimal wall abnormalities. Electrophysiological testing and endomyocardial biopsy were normal.