Age- and Training-Dependent Development of Arrhythmogenic Right Ventricular Cardiomyopathy in Heterozygous Plakoglobin-Deficient Mice

Background— Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disorder that causes sudden death and right ventricular heart failure in the young. Clinical data suggest that competitive sports may provoke ARVC in susceptible persons. Genetically, loss-of-function mutations in desmosomal proteins (plakophilin, desmoplakin, or plakoglobin) have been associated with ARVC. To test the hypothesis that reduced desmosomal protein expression causes ARVC, we studied the cardiac effects of heterozygous plakoglobin deficiency in mice.

Methods and Results— Ten-month-old heterozygous plakoglobin-deficient mice (plakoglobin +/− ) had increased right ventricular volume, reduced right ventricular function, and spontaneous ventricular ectopy (all P <0.05). Left ventricular size and function were not altered. Isolated, perfused plakoglobin +/− hearts had spontaneous ventricular tachycardia of right ventricular origin and prolonged right ventricular conduction times compared with wild-type hearts. Endurance training accelerated the development of right ventricular dysfunction and arrhythmias in plakoglobin +/− mice. Histology and electron microscopy did not identify right ventricular abnormalities in affected animals.

Conclusions— Heterozygous plakoglobin deficiency provokes ARVC. Manifestation of the phenotype is accelerated by endurance training. This suggests a functional role for plakoglobin and training in the development of ARVC.

Cooling for acute ischemic brain damage (cool aid): an open pilot study of induced hypothermia in acute ischemic stroke

BACKGROUND AND PURPOSE

Hypothermia is effective in improving outcome in experimental models of brain infarction. We studied the feasibility and safety of hypothermia in patients with acute ischemic stroke treated with thrombolysis.

METHODS

An open study design was used. All patients presented with major ischemic stroke (National Institutes of Health Stroke Scale [NIHSS] score >15) within 6 hours of onset. After informed consent, patients with a persistent NIHSS score of >8 were treated with hypothermia to 32+/-1 degrees C for 12 to 72 hours depending on vessel patency. All patients were monitored in the neurocritical care unit for complications. A modified Rankin Scale was measured at 90 days and compared with concurrent controls.

RESULTS

Ten patients with a mean age of 71.1+/-14.3 years and an NIHSS score of 19.8+/-3.3 were treated with hypothermia. Nine patients served as concurrent controls. The mean time from symptom onset to thrombolysis was 3.1+/-1.4 hours and from symptom onset to initiation of hypothermia was 6.2+/-1.3 hours. The mean duration of hypothermia was 47.4+/-20.4 hours. Target temperature was achieved in 3.5+/-1.5 hours. Noncritical complications in hypothermia patients included bradycardia (n=5), ventricular ectopy (n=3), hypotension (n=3), melena (n=2), fever after rewarming (n=3), and infections (n=4). Four patients with chronic atrial fibrillation developed rapid ventricular rate, which was noncritical in 2 and critical in 2 patients. Three patients had myocardial infarctions without sequelae. There were 3 deaths in patients undergoing hypothermia. The mean modified Rankin Scale score at 3 months in hypothermia patients was 3.1+/-2.3.

CONCLUSION

Induced hypothermia appears feasible and safe in patients with acute ischemic stroke even after thrombolysis. Refinements of the cooling process, optimal target temperature, duration of therapy, and, most important, clinical efficacy, require further study.

Slow conduction and enhanced anisotropy increase the propensity for ventricular tachyarrhythmias in adult mice with induced deletion of connexin43

BACKGROUND

Connexin 43 (Cx43) is a major determinant of conduction in the ventricular working myocardium of mammals. We investigated the effect of decreased Cx43 expression on conduction velocity and arrhythmogenesis using adult mice with inducible deletion of Cx43.

METHODS AND RESULTS

Cx43Cre-ER(T)/+ mice, in which 1 coding region of the Cx43 gene was replaced by Cre-ER(T), were mated to Cx43fl/fl mice, generating Cx43Cre-ER(T)/fl mice. Application of 4-hydroxytamoxifen (4-OHT) induced Cre-ER(T)-mediated deletion of the floxed Cx43 allele. Epicardial ventricular mapping using a 13x19 multiterminal electrode grid (300-microm spacing) was performed on Langendorff-perfused hearts from Cx43fl/fl plus carrier (n=10), Cx43fl/fl plus 4-OHT (n=10), Cx43 Cre-ER(T)/fl plus carrier (n=9), and Cx43Cre-ER(T)/fl plus 4-OHT (n=10). Cx43 protein amount in group 3 hearts was decreased by 50% compared with group 1. 4-OHT did not affect cardiac protein amounts in group 2 but decreased Cx43 expression up to 95% in group 4 compared with group 3. Epicardial activation of both left ventricle (LV) and right ventricle (RV) during sinus rhythm was similar in all groups. Conduction velocity (CV) changed only in group 4 animals. For RV (LV), longitudinal CV decreased from 38 (35) to 31.6 (33.6) and transverse CV from 24.4 (16.8) to 10.1 (11.3) cm/s. Dispersion of conduction in RV (LV) was increased by 91% (38%). Programmed stimulation resulted in ventricular arrhythmias in group 4 (7 of 10 mice) but never in groups 1 through 3.

CONCLUSIONS

Heterozygous expression of Cx43 did not affect ventricular conduction velocity. Up to 95% decrease of Cx43 protein in 4-OHT-treated Cx43(Cre-ER(T)/fl) mice reduced conduction velocity and increased dispersion of conduction and propensity for ventricular arrhythmias.

Left stellate ganglion and vagal nerve activity and cardiac arrhythmias in ambulatory dogs with pacing-induced congestive heart failure

OBJECTIVES

The purpose of this study was to determine the patterns of autonomic nerve activity in congestive heart failure (CHF).

BACKGROUND

The relationship between autonomic nerve activity and cardiac arrhythmias in CHF is unclear.

METHODS

We implanted radiotransmitters in 6 dogs for continuous (24/7) simultaneous monitoring of left stellate ganglion nerve activity (SGNA), vagal nerve activity (VNA), and electrocardiography before and after pacing-induced CHF.

RESULTS

Congestive heart failure increased both SGNA and VNA. The SGNA but not VNA manifested a circadian variation pattern. There was extensive sinus node fibrosis. We analyzed 2,263 episodes of prolonged (>3 s) sinus pauses (PSP) and 1,420 long (>10 s) episodes of paroxysmal atrial tachycardia (PAT). Most (95.3%) PSP episodes occurred at night, and 56% were preceded by a short burst of SGNA that induced transient sinus tachycardia. Long PAT episodes were typically (83%) induced by simultaneous SGNA and VNA discharge, followed by VNA withdrawal. Premature ventricular contractions and ventricular tachycardia were preceded by elevated SGNA.

CONCLUSIONS

The reduction of sympathovagal balance at night in ambulatory dogs was due to reduced sympathetic discharge rather than a net increase of vagal discharge. The tachybrady syndrome in CHF might be triggered by an intermittent short burst of SGNA that resulted in tachycardia and sinus node suppression. Simultaneous sympathovagal discharge is a cause of long PAT episodes. These data indicate that there is an association between the specific patterns of autonomic nerve discharges and cardiac arrhythmia during CHF.

The Ib phase of ventricular arrhythmias in ischemic in situ porcine heart is related to changes in cell-to-cell electrical coupling. Experimental Cardiology Group, University of North Carolina

BACKGROUND

This study was designed to test the hypothesis that the loss of cell-to-cell electrical interaction during ischemia modulates the amplitude of ischemia-induced TQ-segment depression (ie, the injury potential) and the occurrence of ventricular fibrillation (VF) during the so-called Ib phase of ventricular arrhythmias.

METHODS AND RESULTS

Regional ischemia was induced by 60 minutes of mid-left anterior descending coronary artery ligation in open-chest swine (n = 10). Cell-to-cell electrical uncoupling was defined as the onset of the terminal rise in whole-tissue resistivity (Rt). Local activation times and TQ-segment changes (injury potential) were determined from unipolar electrograms. Extracellular K+ ([K+]e) and pH (pHe) were measured with plunge-wire ion-selective electrodes. VF occurred in 6 of 10 pigs during regional no-flow ischemia between 19 and 30 minutes after the arrest of perfusion. The occurrence of VF was positively correlated to the onset of cell-to-cell electrical uncoupling (R2 = .885). Cell-to-cell electrical uncoupling superimposed on changes of [K+]e and pHe contributed to the failure of impulse propagation between 19 and 30 minutes after the arrest of perfusion. During ischemia, maximum TQ-segment depression was -10 mV at 19 minutes, after which TQ-segment depression slowly recovered. The onset of the TQ-segment recovery was correlated to the second rise in Rt (R2 = .886).

CONCLUSIONS

In the regionally ischemic in situ porcine heart, loss of cell-to-cell electrical interaction is related to the occurrence of VF and changes in the amplitude of the injury current. Cellular electrical uncoupling contributes to failure of impulse propagation in the setting of altered tissue excitability as a result of elevated [K+]e and low pHe. These data indicate that Ib arrhythmias and ECG changes during ischemia are influenced by the loss of cell-to-cell electrical interaction.

Localization of optimal ablation site of idiopathic ventricular tachycardia from right and left ventricular outflow tract by body surface ECG

BACKGROUND

Idiopathic ventricular tachycardia (VT) is known to arise from the right ventricular (RV) and left ventricular outflow tracts (LVOT). However, reliable noninvasive methods to localize the optimum ablation site for VT have not been reported.

METHODS AND RESULTS

Body surface maps (BSM) and 12-lead ECGs were investigated in 35 VTs from the RVOT and 5 VTs from the LVOT in which the origin was confirmed during the ablation procedure. The RVOT was classified into 8 subdivisions with the use of a 3-dimensional anatomic relation: anterior (A) posterior (P), right (R) left (L), and superior (S) inferior (I). On the BSM, the following 3 indexes differentiated each location of the origin, with a diagnostic accuracy of 88% (A-P), 92% (R-L), and 77% (S-I): (1) the location of the minimum at the early-to-mid QRS (right, A; left, P), (2) the isopotential distribution in the left shoulder area after 30 ms of QRS (positive, R; negative, L), and (3) the downward moving time of the minimum at the early-to-mid QRS (>/=50 ms, S; <50 ms, I). On the 12-lead ECG, (1) the QRS duration (>140 ms, A; </=140 ms, P) and the R-wave pattern in leads II and III (RR' or Rr', A, R, P), (2) the QS wave amplitude in aVR and aVL (aVR>/=aVL, R; aVR<aVL, L), and (3) the r-wave amplitude in V1 and V2 (high, S; low, I) localized the origin with 80%, 86% (A-P), 80% (R-L), and 66% (S-I) accuracy. R/S>/=1 in lead V3 was an index suggesting the LVOT origin.

CONCLUSIONS

The origin or the optimum ablation site of idiopathic VT from RVOT and LVOT can be localized with the use of indexes obtained with a BSM or 12-lead ECG.

Long-term outcome in asymptomatic men with exercise-induced premature ventricular depolarizations

BACKGROUND

Exercise testing is widely used in the diagnosis of coronary artery disease, but the long-term outcome for asymptomatic persons with exercise-induced premature ventricular depolarizations remains unclear. We used data from the Paris Prospective Study I to assess the long-term outcome for such persons.

METHODS

A total of 6101 asymptomatic French men (42 to 53 years of age) who were free of clinically detectable cardiovascular disease underwent a standardized graded exercise test between 1967 and 1972. Subjects were prospectively classified as having or not having frequent premature ventricular depolarizations (a run of two or more consecutive premature ventricular depolarizations or premature ventricular depolarizations constituting more than 10 percent of all ventricular depolarizations during any of the 30-second electrocardiographic recordings).

RESULTS

During exercise, 138 subjects had frequent premature ventricular depolarizations. After 23 years of follow-up, these subjects had a higher risk of death from cardiovascular causes than the men without frequent premature ventricular depolarizations during exercise (relative risk, 2.67; 95 percent confidence interval, 1.76 to 4.07). In a multivariate model, with adjustment for age, body-mass index, heart rate at rest, systolic blood pressure, tobacco use, level of physical activity, presence or absence of diabetes, total cholesterol level, and the presence or absence of premature ventricular depolarizations before exercise and during recovery from exercise, both an exercise test that was positive for ischemia and the occurrence of frequent premature ventricular depolarizations during exercise remained independently associated with an increased risk of death from cardiovascular causes, with similar relative risks (2.63 [95 percent confidence interval, 1.93 to 3.59] and 2.53 [95 percent confidence interval, 1.65 to 3.88], respectively).

CONCLUSIONS

The occurrence of frequent premature ventricular depolarizations during exercise in asymptomatic middle-aged men is associated with a long-term increase in the risk of death from cardiovascular causes.

Idiopathic ventricular arrhythmia arising from the mitral annulus

OBJECTIVES

We sought to clarify the prevalence and characteristics of idiopathic ventricular tachycardia or premature ventricular contraction originating from the mitral annulus (MAVT/PVC).

BACKGROUND

Recent case reports have presented patients with MAVT/PVC.

METHODS

Electrocardiographic (ECG) characteristics and the results of electrophysiologic investigation and radiofrequency catheter ablation (RFCA) were analyzed in 352 patients with symptomatic idiopathic ventricular tachycardia (IVT)/premature ventricular contraction (PVC).

RESULTS

Nineteen cases of IVT/PVC (5%) represented MAVT/PVC. Of these, 11 (58%) originated from the anterolateral portion of the mitral annulus (AL-MAVT/PVC), and 2 (11%) arose from the posterior portion (Pos-MAVT/PVC). The remaining six cases of MAVT/PVC (31%) had posteroseptal origin (PS-MAVT/PVC). In all patients, an S-wave was present in lead V(6). The QRS polarity in inferior leads and leads I and aVL was useful for differentiating AL-MAVT/PVC from Pos-MAVT/PVC or PS-MAVT/PVC. The Pos-MAVT/PVC had an Rs pattern in lead I and an R pattern in lead V(1), whereas PS-MAVT/PVC invariably had an R pattern in lead I and a negative QRS component in lead V(1). The AL-MAVT/PVC and Pos-MAVT/PVC showed a longer QRS duration than the PS-MAVT/PVC (p < 0.001), and all had late-phase "notching" of the QRS complex in inferior leads. In all patients, RFCA eliminated MAVT/PVC, with no recurrences during follow-up for 21 +/- 15 months.

CONCLUSIONS

Mitral annular VT/PVC is a rare but distinct subgroup of IVT/PVC. MAVT/PVC origin could be determined by ECG analysis. The AL and PS sites of the MA were preferential.

Efficacy and safety of berberine for congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

This study was designed to assess the efficacy and safety of berberine for chronic congestive heart failure (CHF). One hundred fifty-six patients with CHF and >90 ventricular premature complexes (VPCs) and/or nonsustained ventricular tachycardia (VT) on 24-hour Holter monitoring were randomly divided into 2 groups. All patients were given conventional therapy for CHF, consisting of angiotensin-converting enzyme inhibitors, digoxin, diuretics, and nitrates. Patients in the treatment group (n = 79) were also given berberine 1.2 to 2.0 g/day. The remaining 77 patients were given placebo. Symptoms, a 6-minute walk test, left ventricular (LV) ejection fraction (EF), frequency and complexity of VPCs, and quality of life were assessed after 8 weeks of treatment and during a mean 24-month follow-up. After treatment with berberine, there was a significantly greater increase in LVEF, exercise capacity, improvement of the dyspnea-fatigue index, and a decrease of frequency and complexity of VPCs compared with the control group. There was a significant decrease in mortality in the berberine-treated patients during long-term follow-up (7 patients receiving treatment died vs 13 on placebo, p <0.02). Proarrhythmia was not observed, and there were no apparent side effects. Thus, berberine improved quality of life and decreased VPCs and mortality in patients with CHF.

Idiopathic ventricular arrhythmias originating from the tricuspid annulus: Prevalence, electrocardiographic characteristics, and results of radiofrequency catheter ablation

BACKGROUND

Idiopathic ventricular tachycardias (VTs) and premature ventricular contractions (PVCs) arising from the tricuspid annulus have been reported.

OBJECTIVE

The purpose of this study was to clarify the prevalence and characteristics of VT/PVCs originating from the tricuspid annulus.

METHODS

The ECG characteristics and results of radiofrequency (RF) catheter ablation were analyzed in 454 patients with idiopathic VT/PVCs.

RESULTS

Thirty-eight (8%) patients had VT/PVCs arising from the tricuspid annulus: 28 VT/PVCs (74%) originated from the septal portion of the tricuspid annulus and the remaining 10 (26%) from the free wall of the tricuspid annulus. QRS duration and Q-wave amplitude in each of leads V1-V3 were greater in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (all P < .01). "Notching" of the QRS complex was observed more often in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (P < .01). A Q wave in lead V1 was observed more often in VT/PVCs arising from the septum of the tricuspid annulus than those from the free wall of the tricuspid annulus (P < .005). R-wave transition occurred beyond lead V3 more often in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (P < .005). RF catheter ablation eliminated 90% of the VT/PVCs arising from the free wall of the tricuspid annulus but only 57% of the VT/PVCs arising from septum of the tricuspid annulus.

CONCLUSION

Idiopathic VT/PVCs arising from tricuspid annulus are not rare, and the detailed origin can be determined by ECG analysis. The preferential site of origin was the septum but also could be the free wall of the tricuspid annulus.

Natural history of Brugada syndrome: the prognostic value of programmed electrical stimulation of the heart

INTRODUCTION

The prognostic value of electrophysiologic studies in individuals with the syndrome of right bundle branch block and ST segment elevation in precordial leads V1 to V3 (Brugada syndrome) remains controversial. Our previous data from 252 individuals with the syndrome suggested that programmed ventricular stimulation had a good overall accuracy to predict events. However, studies from independent investigators questioned our results. We report here the largest population with Brugada syndrome ever studied by programmed electrical stimulation of the heart.

METHODS AND RESULTS

Four hundred forty-three individuals with an ECG diagnostic of Brugada syndrome were studied by programmed electrical stimulation of the heart. The diagnosis was made because of the classic ECG showing a coved-type ST segment elevation in precordial leads V1 to V3. Of the 443 individuals, 180 had developed spontaneous symptoms (syncope or aborted sudden cardiac death) and 263 were asymptomatic at the time the diagnosis was made. The ventricular stimulation protocol included a minimum of two basic pacing cycle lengths with two ventricular premature beats from the right ventricular apex. A sustained ventricular arrhythmia was induced in 217 cases (49%). Symptomatic patients were more frequently inducible [126/180 (70%)] than asymptomatic individuals [91/263 (34%); P = 0.0001]. Males were more frequently inducible than females (54% vs 32%, P < 0.0001). Inducible individuals had a longer HV interval than noninducible patients (50 +/- 12 msec vs 46 +/- 10 msec, P < 0.002). HV interval and number of premature beats needed to induce VF were not related to outcome. Inducibility was statistically a powerful predictor of arrhythmic events during follow-up. Sixty of 217 inducible patients (28%) had spontaneous ventricular fibrillation compared with 5 of 221 noninducible patients (2%; P = 0.0001).

CONCLUSION

Inducibility of sustained ventricular arrhythmias during programmed ventricular stimulation of the heart is a good predictor of outcome in Brugada syndrome.

Suppression of frequent premature ventricular contractions and improvement of left ventricular function in patients with presumed idiopathic dilated cardiomyopathy

OBJECTIVE

To examine the hypothesis that suppression of frequent premature ventricular contractions may be associated with improvement in left ventricular function in patients with presumed idiopathic dilated cardiomyopathy.

DESIGN

We conducted a retrospective case study and statistical analysis of the effect of cardiac medical therapy on outcome.

MATERIAL AND METHODS

The study population consisted of 14 patients with more than 20,000 premature ventricular contractions in 24 hours recorded by Holter monitoring and associated left ventricular dysfunction (ejection fraction, 40% or less). Clinical characteristics, number of premature ventricular contractions per hour on 24-hour ambulatory Holter monitoring, and ejection fraction based on transthoracic echocardiography were compared before and after cardiac therapeutic intervention.

RESULTS

Of the 14 patients, 10 had presumed idiopathic dilated cardiomyopathy, and 4 had ischemic heart disease. Of the overall study group, seven had received additional cardiac medical therapy after the index evaluation, including four patients who had amiodarone therapy. A significant reduction (75% or more from baseline) in premature ventricular contractions after medical therapeutic intervention was observed in five patients at the first follow-up examination. The mean interval to the first follow-up examination was 6 +/- 3 months. Of the five patients, four had significant improvement in clinical functional status and the ejection fraction. The mean ejection fraction of these five patients increased from 27 +/- 10% at baseline to 49 +/- 17% after medical therapy (P = 0.04).

CONCLUSION

The suppression of frequent premature ventricular contractions may be associated with improvement of left ventricular function in patients with presumed idiopathic dilated cardiomyopathy.

Distinction between arrhythmic and nonarrhythmic death after acute myocardial infarction based on heart rate variability, signal-averaged electrocardiogram, ventricular arrhythmias and left ventricular ejection fraction

OBJECTIVES

We investigated whether heart rate variability, the signal-averaged electrocardiogram (ECG), ventricular arrhythmias and left ventricular ejection fraction predict the mechanism of cardiac death after myocardial infarction.

BACKGROUND

Postinfarction risk stratification studies have almost exclusively focused on predicting the risk of arrhythmic death. The factors that identify and distinguish persons at risk for arrhythmic and nonarrhythmic death are poorly known.

METHODS

Heart rate variability, the signal-averaged ECG, ventricular arrhythmias and left ventricular ejection fraction were assessed in 575 survivors of acute myocardial infarction. The patients were followed up for 2 years; arrhythmic and nonarrhythmic cardiac deaths were used as clinical end points. During the follow-up period, 47 cardiac deaths occurred, 29 (62%) arrhythmic and 18 (38%) nonarrhythmic.

RESULTS

All risk factors were associated with cardiac mortality in univariate analysis. With the exception of left ventricular ejection fraction, they were also predictors of arrhythmic death. Depressed heart rate variability (p < 0.001), ventricular ectopic beats (p < 0.001) and low ejection fraction (p < 0.001) were related to nonarrhythmic death. In multivariate analysis, depressed heart rate variability (p < 0.001) and runs of ventricular tachycardia (p < 0.05) predicted arrhythmic death. Nonarrhythmic death was associated with depressed heart rate variability (p < 0.001), ventricular ectopic beats (p < 0.001) and low ejection fraction (p < 0.01). By selecting patients with depressed heart rate variability, long filtered QRS duration or ventricular arrhythmias and excluding patients with the lowest ejection fraction, we identified a group in which 75% of deaths were arrhythmic. Similarly, by selecting patients with a low ejection fraction and excluding patients with the lowest heart rate variability, we identified a group in which 75% of deaths were nonarrhythmic.

CONCLUSIONS

Arrhythmic death was associated predominantly with depressed heart rate variability and ventricular tachycardia runs, and nonarrhythmic death with low ejection fraction, ventricular ectopic beats and depressed heart rate variability. A combination of risk factors identified patient groups in which a majority of deaths were either arrhythmic or nonarrhythmic.

Prevalence of premature ventricular contractions in a population of African American and white men and women: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

The distribution or the causes of premature ventricular contractions (PVCs) in diverse populations are not fully known. We describe the prevalence of PVCs on a 2-minute electrocardiogram (ECG) in adults to determine whether hypertension has an important association with such PVCs.

METHODS

A cross-sectional analysis of the 15,792 individuals (aged 45-65 years) from the four US communities participating at visit 1 of the Atherosclerosis Risk In Communities (ARIC) study was performed. Multiple logistic regression was used to determine the association of PVCs with potential causal predictors of PVCs.

RESULTS

Based on a 2-minute ECG, PVCs are present in >6% of middle-aged adults. Increasing age, the presence of heart disease, faster sinus rates, African American ethnicity, male sex, lower educational attainment, and lower serum magnesium or potassium levels are directly related to PVC prevalence. Independently of these factors, hypertension is associated with a 23% increase in the prevalence of PVCs.

CONCLUSIONS

The prevalence of PVCs on a 2-minute ECG differs by age, ethnicity, and sex and is associated with hypertension, heart disease, faster sinus rates, electrolyte abnormalities, and lower educational attainment. Hypertension is likely to be a major cause of PVCs in adults.

In vivo detection of coronary artery anomalies in asymptomatic athletes by echocardiographic screening

BACKGROUND

Anomalous origin of coronary arteries (AOCA) is a rare congenital disease. Although it may have a benign course, it has been identified as a frequent cause of sports-related sudden death. Unfortunately, in vivo detection of AOCA is not easy, as individuals with this anomaly often are asymptomatic and show no signs of myocardial ischemia. Presently, transthoracic two-dimensional echocardiography (TTE) is the only noninvasive, widely available tool to visualize the ostia and first tracts of coronary arteries.

OBJECTIVE

To assess the efficacy of TTE in the screening of AOCA in a large athletic population.

STUDY DESIGN

In a prospective study, we assessed the ostia and first tracts of coronary arteries in 3,650 subjects (mean age, 30+/-12 years) practicing different sports at various competitive levels. Subjects underwent a TTE examination in our laboratory for scientific or diagnostic purposes.

RESULTS

Technically satisfactory echocardiograms were obtained in 3,504 subjects (96%); a clear visualization of the ostia and first tracts of both coronary arteries was obtained in 3,150 cases (90%). Three asymptomatic athletes (0.09%) were suspected to have an AOCA; two with a right coronary artery origin from the left sinus, and one with a left coronary artery origin from the right sinus. Diagnosis was confirmed by coronary angiography.

CONCLUSIONS

Our study indicated that AOCA is rare in asymptomatic athletes. Systematic and accurate exploration of coronary anatomy in athletes referred for a diagnostic TTE examination may be useful in identifying those with AOCA.

Premature ventricular contractions during triggered imaging with ultrasound contrast

BACKGROUND

Premature ventricular contractions (PVCs) were observed during triggered second harmonic imaging of a contrast agent for myocardial perfusion assessment, with continuous infusion of the contrast agent. Further investigation into the relation of this phenomenon to both ultrasound energy and the contrast agent was carried out during a subsequent bolus-versus-infusion study.

METHODS AND RESULTS

Two open-label studies in healthy male volunteers were performed. The initial study was a dose-response study in 10 subjects, which compared 3 infusion rates. Each volunteer received 3 continuous infusions with different infusion rates of the contrast agent for either 10 (n = 6) or 20 (n = 4) minutes. End-systolic triggered imaging with a mechanical index (MI) of 1.5 was used throughout this part of the study. The second study compared bolus injection with a continuous infusion in 9 volunteers, with a single-dose level but different imaging modalities: end-systolic and end-diastolic triggered imaging at MIs of both 1.1 and 1.5. Spontaneous baseline PVCs were uncommon: 10 in 344 minutes (0.03 PVC/min, maximal 1 PVC/min) of baseline imaging. During end-diastolic triggering, no increase in PVCs was seen, irrespective of MI. A significant increase to 1.06 PVC/min (P <.001) was seen during end-systolic imaging with an MI of 1.5, but not with an MI of 1.1. The increase in PVC rate was dose-dependent in the initial study.

CONCLUSION

Imaging of contrast agents with high acoustic pressures can cause PVCs if end-systolic triggering is used. This effect is related to both the dose of contrast agent and acoustic pressure. It does not occur during end-diastolic triggered imaging. Precautionary measures would include using lower MIs or end-diastolic triggering.

Effects of ventricular premature stimulus coupling interval on blood pressure and heart rate turbulence

BACKGROUND

Heart rate turbulence (HRT) is a promising noninvasive risk stratifier for mortality after myocardial infarction. On the basis of a study of ventricular premature complex coupling interval and sympathetic nerve burst amplitude, we hypothesized that measures of HRT would increase with increased prematurity of the coupling interval.

METHODS AND RESULTS

Twenty-eight patients undergoing programmed electrical stimulation were studied (12 with prior myocardial infarction, aged 60+/-18 years). An extrastimulus was delivered from the right ventricular apex after 20 sinus beats with a V-S(2) coupling interval decremented by 20 to 30 ms until refractoriness was reached. Turbulence slope (TS), turbulence timing (TT), and turbulence onset were calculated for each extrastimulus, and the linear regressions of these parameters on coupling interval and compensatory pause were calculated. Arterial blood pressure was measured with arterial catheter or a noninvasive continuous blood pressure transducer (Buffington cuff). TS and turbulence onset were abnormal in 4 and 13 patients, respectively. HRT parameters were significantly correlated with coupling interval or compensatory pause in only 2 or 3 patients for a given regression analysis. This absence of correlation was found likely to be due to lack of correlation between compensatory pause and systolic blood pressure after the compensatory pause. Heart rate and TS were correlated: Patients with high heart rate had low TS and late TT (TS=-2.7+0.01xsinus cycle length, P=0.018; TT=8.8 to 0.005xsinus cycle length, P=0.013).

CONCLUSIONS

HRT can be induced by programmed stimulation. In this setting, heart rate affects HRT but not ventricular premature complex prematurity. Induced HRT seems to be a valid method for measuring HRT parameters in patients with few ventricular premature complexes.

Provocation of Ventricular Ectopy by Cheyne-Stokes Respiration in Patients with Heart Failure

STUDY OBJECTIVES

Previous reports have suggested an association between Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) and ventricular ectopy, but there has been relatively little evidence of a cause-effect relationship. The objective of this study was to determine whether CSR-CSA directly provokes ventricular ectopy and, if so, whether it is associated with any particular phase of the CSR-CSA breathing cycle.

DESIGN

We compared the frequency of ventricular premature beats (1) between the apneic and hyperpneic phases of CSR-CSA, (2) between periods of CSR-CSA and periods of regular breathing during sleep, and (3) in response to the elimination of CSR-CSA by administration of a low concentration of inhaled CO2.

SETTING

Hospital-based cardiopulmonary sleep laboratory.

PATIENTS

Twenty-three patients with heart failure and CSR-CSA.

MEASUREMENTS AND RESULTS

Ventricular premature beats were found to occur 40% more frequently during the hyperpneic phase than the apneic phase of CSR-CSA (mean+/-SD, 7.0+/-7.4 versus 4.9+/-5.7 ventricular premature beats per minute, P = .003). Ventricular premature beat frequency was also found to be higher during periods of CSR-CSA than during periods of regular breathing occurring either spontaneously (median [25th, 75th percentile], 2.2 [1.2, 6.5] versus 1.1 [0.8, 2.0] ventricular premature beats per minute, P = .027), or induced through inhalation of CO2 (from 4.7+/-3.8 to 3.3+/-4.0 ventricular premature beats per minute, P = .048).

CONCLUSIONS

CSR-CSA provokes ventricular ectopy that is most pronounced during the hyperpneic phase. Such an increase in ventricular premature beats might contribute to the higher mortality rates reported in heart failure patients with CSR-CSA.

Electrocardiographic changes during exposure to residual oil fly ash (ROFA) particles in a rat model of myocardial infarction

Epidemiological studies have reported a positive association of short-term increases in ambient particulate matter (PM) with daily mortality and hospital admissions for cardiovascular disease. Although patients with cardiopulmonary disease appear to be most at risk, particulate-related cardiac effects following myocardial infarction (MI) have not been examined. To improve understanding of mechanisms, we developed and tested a model for investigating the effects of inhaled PM on arrhythmias and heart rate variability (HRV), a measure of autonomic nervous system activity, in rats with acute MI. Left-ventricular MI was induced in 31 Sprague-Dawley rats by thermocoagulation of the left coronary artery; 32 additional rats served as sham-operated controls. Diazepam-sedated rats were exposed (1 h) to residual oil fly ash (ROFA), carbon black, or room air at 12-18 h after surgery. Each exposure was immediately preceded and followed by a 1-h exposure to room air (baseline and recovery periods, respectively). Lead-II electrocardiograms were recorded. In the MI group, 41% of rats exhibited one or more premature ventricular complexes (PVCs) during the baseline period. Exposure to ROFA, but not to carbon black or room air, increased arrhythmia frequency in animals with preexisting PVCs. Furthermore, MI rats exposed to ROFA, but not to carbon black or room air, decreased HRV. There was no difference in arrhythmia frequency or HRV among sham-operated animals. These results underscore the usefulness of this model for elucidating the physiologic mechanisms of pollution-induced cardiovascular arrhythmias and contribute to defining the specific constituents of ambient particles responsible for arrhythmias.

Clinical Correlates and Prognostic Significance of Exercise-Induced Ventricular Premature Beats in the Community

Background— Recent investigations suggest that ventricular premature beats during exercise (EVPBs) are associated with increased cardiovascular mortality in asymptomatic individuals, but mechanisms underlying the association are unclear.

Method and Results— We evaluated 2885 Framingham Offspring Study participants (1397 men; mean age, 43 years) who were free of cardiovascular disease and who underwent a routine exercise stress test; 792 participants (27%) had development of EVPBs (median, 0.22/min of exercise). Logistic regression was used to evaluate predictors of EVPBs. Cox models were used to examine the relations of infrequent (less than or equal to median) and frequent (greater than median) versus no EVPBs to incidence of hard coronary heart disease (CHD) event (recognized myocardial infarction, coronary insufficiency, or CHD death) and all-cause mortality, adjusting for vascular risk factors and exercise variables. Age and male sex were key correlates of EVPBs. During follow-up (mean, 15 years), 142 (113 men) had a first hard CHD event and 171 participants (109 men) died. EVPBs were not associated with hard CHD events but were associated with increased all-cause mortality rates (multivariable-adjusted hazards ratio, 1.86, 95% CI, 1.24 to 2.79 for infrequent, and 1.71, 95% CI, 1.18 to 2.49 for frequent EVPBs versus none). The relations of EVPBs to mortality risk were not influenced by VPB grade, presence of recovery VPBs, left ventricular dysfunction, or an ischemic ST-segment response.

Conclusions— In our large, community-based sample of asymptomatic individuals, EVPBs were associated with increased risk of death at a much lower threshold than previously reported. Additional studies are needed to confirm these findings and to clarify the underlying mechanisms.

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.

Sex-specific triggers for right ventricular outflow tract tachycardia

BACKGROUND

Right ventricular outflow tract tachycardia (RVOT-VT) is a common arrhythmia in young patients without heart disease. The arrhythmia is characterized by repetitive bursts and premature ventricular contractions with a left bundle branch block, inferior-axis QRS morphology, and symptoms of palpitations. Although more frequent in women, sex-specific triggers for symptomatic RVOT-VT have not been identified.

METHODS AND RESULTS

We interviewed 34 women and 13 men referred for ablation of RVOT-VT to determine if predictable but sex-specific exacerbations in symptomatic RVOT-VT exist. After a general query asking if there was predictability to what triggered palpitations, we then specifically queried all patients about symptomatic RVOT-VT initiation with exercise, stress, caffeine, fatigue, and, in women only, periods of recognized hormonal flux. The times identified as states of hormonal flux included premenstrual, gestational, perimenopausal, and coincident with the administration of birth control pills. In response to the completed interview, the most common recorded trigger for RVOT-VT in women was recognized states of hormonal flux with 20 (59%) of 34 women responding positively and 14 (41%) of the 34 indicating that states of hormonal flux were the only recognizable triggers. Men were more likely than women to report that their RVOT-VT was predictably triggered by exercise, stress, or caffeine: 12 (92%) of 13 men versus 14 (41%) of 34 women (P <.01).

CONCLUSIONS

Triggers for RVOT-VT initiation are sex specific. Women have RVOT-VT initiation with recognized states of hormonal flux. Men more commonly have RVOT-VT initiated by exercise or stress. These data have important implications related to patient education and counseling in the setting of RVOT-VT and may influence the timing of drug treatment and electrophysiologic evaluation in selected patients.

Classification and mechanism of initiation in patients with congenital long QT syndrome

AIMS

To examine the initiating mode of Torsade de Pointes (TdP) in patients with congenital long QT syndrome (LQTS).

METHODS AND RESULTS

We evaluated 111 episodes of TdP recorded on the electrocardiograms of 24 patients with congenital LQTS, and clarified the initiating mode, the three consecutive preceding RR intervals defined as C(2), C(1), and C(0), the timing of initiating premature ventricular contraction (PVC) and the cycle length (CL) of TdP. Three different initiating patterns were observed: (1) a "short-long-short" sequence (SLS) pattern (23 patients, 72 TdP, 65%) defined as one or more short-long cardiac cycles followed by an initiating short-coupled PVC (C(1)>C(2) and C(0)), (2) an "increased sinus rate" (ISR) pattern (8 patients, 28 TdP, 25%) defined as a gradual increase in sinus rate with or without T-wave alternans (C(2)>/=C(1)>/=C(0)), and (3) a "changed depolarization" (CD) pattern (5 patients, 11 TdP, 10%) defined as a sudden long-coupled PVC or fusion beat followed by short-coupled PVC. The C(0) was shorter in ISR than SLS and CD (mean C(0): 488 vs. 587 and 603 ms, respectively; P<0.05). Therefore, the initiating PVC appeared near the T-wave peak of the last beat before onset in ISR, while it occurred after the T-wave peak in SLS and CD. The CL of TdP was shorter in ISR than in SLS (256 vs. 295 ms, P<0.05).

CONCLUSIONS

Our data show the existence of three predominant initiating modes of TdP in patients with congenital LQTS and suggests a differential mechanism of initiation of TdP for each mode.