Robust Neural-Network-Based Classification of Premature Ventricular Contractions Using Wavelet Transform and Timing Interval Features

Automatic electrocardiogram (ECG) beat classification is essential to timely diagnosis of dangerous heart conditions. Specifically, accurate detection of premature ventricular contractions (PVCs) is imperative to prepare for the possible onset of life-threatening arrhythmias. Although many groups have developed highly accurate algorithms for detecting PVC beats, results have generally been limited to relatively small data sets. Additionally, many of the highest classification accuracies (> 90%) have been achieved in experiments where training and testing sets overlapped significantly. Expanding the overall data set greatly reduces overall accuracy due to significant variation in ECG morphology among different patients. As a result, we believe that morphological information must be coupled with timing information, which is more constant among patients, in order to achieve high classification accuracy for larger data sets. With this approach, we combined wavelet-transformed ECG waves with timing information as our feature set for classification. We used select waveforms of 18 files of the MIT/BIH arrhythmia database, which provides an annotated collection of normal and arrhythmic beats, for training our neural-network classifier. We then tested the classifier on these 18 training files as well as 22 other files from the database. The accuracy was 95.16% over 93,281 beats from all 40 files, and 96.82% over the 22 files outside the training set in differentiating normal, PVC, and other beats.

Beneficial effect of deep breathing on premature ventricular complexes: can it be related to the decrease in QT dispersion?

It has been reported that deep breathing at 6 breaths/min is associated with reduction of premature ventricular complexes. The beneficial effect of deep breathing is supposed to be due to vagal modulation of sinoatrial and atrioventricular node. Beside the modulating effects of deep breathing, we believe that deep breathing, which is also used in yoga training, might have additional effects via decreasing QT dispersion.

Heart rate turbulence parameters correlate with post-premature ventricular contraction changes in muscle sympathetic activity

BACKGROUND

Heart rate turbulence (HRT) has been shown to be vagally mediated with a strong correlation to baroreflex indices. However, the relationship between HRT and peripheral sympathetic nerve activity (SNA) after a premature ventricular contraction (PVC) remains unclear.

OBJECTIVE

We sought to evaluate the relationship between HRT and the changes in peripheral SNA after PVCs.

METHODS

We recorded postganglionic muscle SNA during electrocardiogram monitoring in eight patients with spontaneous PVCs. Fifty-two PVCs were observed and analyzed for turbulence onset (TO) and slope (TS). SNA was quantified during (1) the dominant burst after the PVC (dominant burst area) and (2) the 10 seconds after the dominant burst (postburst SNA).

RESULTS

The mean TO was 0.1% +/- 4.6%, and the mean TS was 6.1 +/- 6.6. The dominant burst area negatively correlated with TO (r = -0.50, P = .0002). The postburst SNA showed a significant positive correlation with TO (r = 0.44, P = .001) and a negative correlation with TS (r = -0.42, P = .002). These correlations remained significant after controlling for either the PVC coupling interval or the left ventricular ejection fraction.

CONCLUSIONS

Our findings highlight the relationship between perturbations in HRT and pathology in the sympathetic limb of the autonomic nervous system. Future studies are needed to evaluate the prognostic role of baroreflex control of sympathetic activity in patients with structural heart disease.

Glibenclamide attenuates the antiarrhythmic effect of endotoxin with a mechanism not involving K(ATP) channels

The role of K(ATP) channels in the antiarrhythmic effect of Escherichia coli endotoxin-induced nitric oxide synthase (iNOS) was examined in an anesthetised rat model of myocardial ischemia and reperfusion arrhythmia by using glibenclamide (1 mg kg(-1)), nateglinide (10 mg kg(-1)) and repaglinide (0.5 mg kg(-1)). Endotoxin (1 mg kg(-1)) was administered intraperitoneally 4 h before the occlusion of the left coronary artery and glibenclamide, nateglinide or repaglinide was administered 30 min before coronary artery occlusion. We also evaluated the effects of K(ATP) channel blockers and nonselective K(+) channel blocker tetraethylammonium (TEA) on cardiac action potential configuration in the atria obtained from endotoxemic rats. The mean arterial blood pressure of rats receiving endotoxin was lower during both the occlusion and reperfusion periods. Endotoxin significantly reduced the total number of ectopic beats and the duration of ventricular tachycardia. Glibenclamide, but not nateglinide and repaglinide, prevented the hypotension and antiarrhythmic effects of endotoxin. Atria obtained from endotoxin-treated rats had prolonged action potential duration. This effect was abolished with pretreatment of iNOS inhibitors, l-canavanine and dexamethasone and perfusion of glibenclamide, but not with TEA and non-sulfonylurea drug, nateglinide. We demonstrated that glibenclamide inhibits the antiarrhythmic effect of endotoxin and this effect does not appear to involve K(ATP) channels.

Respiratory modulation of the autonomic nervous system during Cheyne-Stokes respiration

Cheyne-Stokes respiration (CSR) is associated with increased mortality among patients with heart failure. However, the specific link between CSR and mortality remains unclear. One possibility is that CSR results in excitation of the sympathetic nervous system. This review relates evidence that CSR exerts acute effects on the autonomic nervous system during sleep, and thereby influences a number of cardiovascular phenomena, including heart rate, blood pressure, atrioventricular conduction, and ventricular ectopy. In patients in sinus rhythm, heart rate and blood pressure oscillate during CSR in association with respiratory oscillations, such that both peak heart rate and blood pressure occur during the hyperpneic phase. Inhalation of CO2 abolishes both CSR and the associated oscillations in heart rate and blood pressure. In contrast, O2 inhalation sufficient to eliminate hypoxic dips has no significant effect on CSR, heart rate, or blood pressure. In patients with atrial fibrillation, ventricular rate oscillates in association with CSR despite the absence of within-breath respiratory arrhythmia. The comparison of RR intervals between the apneic and hyperpneic phases of CSR indicates that this breathing disorder exerts its effect on ventricular rate by inducing cyclical changes in atrioventricular node conduction properties. In patients with frequent ventricular premature beats (VPBs), VPBs occur more frequently during the hyperpneic phase than the apneic phase of CSR. VPB frequency is also higher during periods of CSR than during periods of regular breathing, with or without correction of hypoxia. In summary, CSR exerts multiple effects on the cardiovascular system that are likely manifestations of respiratory modulation of autonomic activity. It is speculated that the rhythmic oscillations in autonomic tone brought about by CSR may ultimately contribute to the sympatho-excitation and increased mortality long observed in patients with heart failure and CSR.

Effect of deep breathing at six breaths per minute on the frequency of premature ventricular complexes

Although the effect of reflex increase in vagal tone on the frequency of premature ventricular complexes (PVC) is known, the effect of timed deep breathing on the frequency of PVC has not been reported. We serendipitously discovered that deep breathing at six breaths per minute abolished PVC in an 18-year-old female with frequent PVC, anxiety, and palpitations. In five of a series of 10 consecutive patients with frequent (> or = 10/min) unifocal PVC, deep breathing at 6 breaths/min reduced the frequency of PVC by at least 50%. This is possibly due to increased vagal modulation of sinoatrial and atrioventricular node. However, factors predicting the response to deep breathing, and the mechanisms involved need to be studied in a larger number of patients.

Electrocardiographic Diagnosis of Myocardial Infarction during Left Bundle Branch Block

The electrocardiographic diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) has long been considered problematic or even almost impossible. Many proposed ECG markers in the old literature have now been discarded. However, the advent of reperfusion therapy has generated greater interest in the ECG diagnosis of acute MI in LBBB where ST-segment deviation is the only useful sign. As such, the ST-segment criteria cannot be used to rule out MI, but they can help to rule it in. Criteria for old MI (based on QRS changes) have not been reevaluated for almost 20 years and continue to exhibit low sensitivity, but high specificity.

Relation of ventricular premature complexes during recovery from a myocardial perfusion exercise stress test to myocardial ischemia

Ventricular premature complexes (VPCs) during exercise have long been believed to be harbingers of increased mortality. A recent study has shown that VPCs during the recovery phase of a treadmill exercise test are more predictive of mortality than VPCs that develop during exercise. However, no study to date has examined the relation of VPCs in recovery to the presence of ischemia on myocardial perfusion imaging. We examined the database of perfusion imaging at the Duke University Medical Center from September 1993 to July 2003. We examined the incidence of VPCs during exercise, during the recovery phase, and during the 2 phases. Logistic regression modeling was used to evaluate the significance of VPCs during stress and during recovery in predicting ischemia. VPCs developed during recovery in 561 of 2,828 patients (19.8%). Compared with patients without VPCs during recovery, those with VPCs during recovery were more likely to have a history of hypertension (64.0% vs 56.9%, p = 0.002) and previous coronary artery bypass grafting (25.3% vs 17.1%, p = 0.001). They were also more likely to be older, men, and Caucasian, and to have 3-vessel coronary artery disease (31.9% vs 21.0%, p = 0.001). After adjusting for differences in patient characteristics, VPCs during recovery were significantly associated with ischemia (odds ratio 1.27, 95% confidence interval 1.04 to 1.56, p = 0.017), whereas VPCs during stress were not (p = 0.128). In conclusion, VPCs during the recovery phase of an exercise study are predictive of ischemia on myocardial perfusion imaging.

Ambulatory electrocardiogram analysis in infants treated with recombinant human acid α-glucosidase enzyme replacement therapy for Pompe disease

PURPOSE

Infantile Pompe disease is caused by deficiency of lysosomal acid alpha-glucosidase. Trials with recombinant human acid alpha-glucosidase enzyme replacement therapy (ERT) show a decrease in left ventricular mass and improved function. We evaluated 24-hour ambulatory electrocardiograms (ECGs) at baseline and during ERT in patients with infantile Pompe disease.

METHODS

Thirty-two ambulatory ECGs were evaluated for 12 patients with infantile Pompe disease from 2003 to 2005. Patients had a median age of 7.4 months (2.9-37.8 months) at initiation of ERT. Ambulatory ECGs were obtained at determined intervals and analyzed.

RESULTS

Significant ectopy was present in 2 of 12 patients. Patient 1 had 211 and 229 premature ventricular contractions (0.2% of heart beats) at baseline and at 11.5 weeks of ERT, respectively. Patient 2 had 10,445 premature ventricular contractions (6.7% of heart beats) at 11 weeks of therapy.

CONCLUSION

Infantile Pompe disease may have preexisting ectopy; it may also develop during the course of ERT. Therefore, routinely monitoring patients using 24-hour ambulatory ECGs is useful. Periods of highest risk may be early in the course of ERT when there is a substantial decrease in left ventricular mass and an initial decrease in ejection fraction.

[Study on pathological rhythm of traditional Chinese medicine about circadian distribution of premature ventricular contractions in 240 patients with viral myocarditis]

OBJECTIVE

To explore the circadian distribution of premature ventricular contractions (PVCs) in patients with viral myocarditis (VM) according to the theory of chronomedicine in traditional Chinese medicine (TCM) in order to find out the scientific evidence for a reasonable administration time.

METHODS

Two hundred and forty patients with VM were enrolled and electrocardiograms were examined for all by Holter monitor. The circadian distribution of PVCs was evaluated according to the theory of chronomedicine of TCM about time periods corresponding to five zang viscera.

RESULTS

PVCs mostly happened in periods of 3:00-5:00, 5:00-7:00, 7:00-9:00 and 9:00-11:00, in which 5:00-7:00 was the most serious time. Less PVCs happened in periods of 17:00-19:00, 19:00-21:00 and 21:00-23:00. The frequency of PVCs in midnight also increased with aging. The time periods of the frequency peak of PVCs in patients with different syndromes were also different. In patients with syndrome of pathogenic heat invading heart (PHIH), the PVCs mostly appeared in midday. In patients with syndrome of flaring of fire due to yin-deficiency (FFYD), the PVCs were most serious in daytime and aggravated at noon. And in patients with syndrome of insufficiency of heart-qi and yang (IHQY), the PVCs mostly happened in early morning or midnight.

CONCLUSION

There was a manifest regulation of the pathological circadian rhythm of PVCs in patients with VM. The circadian distributions of PVCs were variable in patients with different syndromes. Therefore the theory of chronomedicine of TCM may be used to guide the treatment based on syndrome differentiation.

Abnormalities in fractal heart rate dynamics in Chagas disease

BACKGROUND AND METHODS

In order to study fractal HR dynamics in Chagas disease, we performed detrended fluctuation analysis (DFA)-along with analysis of power-law beta slope (beta index) and standard deviation of N-N intervals (SDNN)-in edited and unedited (with ventricular premature beats - VPBs, only in DFA analysis) series of R-R intervals from Holter monitoring of healthy controls (Group 0, n = 27) and Chagas disease patients with left ventricular (LV) ejection fraction >50% (Group 1, n = 137) and with LV ejection fraction <50% (Group 2, n = 23).

RESULTS

When analyzed from the edited R-R interval data, the long-term scaling exponent alpha(2) is altered both among the Chagas patients with and without LV dysfunction. The short-term scaling exponent alpha(1) was higher in Group 1 Chagas patients as compared to controls (P < 0.01) and did not differ between Group 2 and controls. In unedited R-R interval series, alpha(1) was significantly reduced in Group 2 Chagas patients (0.55 +/- 0.002) as compared to controls (0.90 +/- 0.002) and Group 1 (0.91 +/- 0.003) (P < 0.001), but did not differ between Group 1 and controls. Similarly alpha(2) was lower in Group 2 compared to other groups (P < 0.001). SDNN did not differ between the groups, but the beta index derived from 1/f model was reduced both in Group 1 and 2 Chagas patients as compared to controls (P < 0.01). There was strong correlation (rs = 0.82; P < 0.001) between the beta and alpha(2) index from edited series. There was an inverse correlation (rs =-0.63, P < 0.01) between the number of VPBs and alpha(1) index of unedited series.

CONCLUSIONS

The long-term fractal HR dynamics altered in chagasic patients with and without LV dysfunction could be an early sign of autonomic dysfunction. Patients with impaired LV function show marked alterations in short-term fractal HR dynamics toward more random behavior, mainly due to frequent ectopy. Prospective studies are necessary to define the value of these indices as predictors of death in Chagas disease.

Hemodynamics and Autonomic Control of Heart Rate Turbulence

INTRODUCTION

Late heart rate deceleration parallels the increase of systolic blood pressure during heart rate turbulence (HRT) after ventricular premature complexes (VPC). This is consistent with the involvement of baroreflex mechanism. Physiological background of systolic blood pressure dynamics is not known. Enhanced sympathetic activation and nonautonomic post-VPC changes of stroke volume have been speculated on.

METHODS AND RESULTS

We studied 28 subjects (aged 56 +/- 11 years; 20 males; 18 normal and 10 abnormal left ventricular (LV) function) with spontaneous occurrence of VPCs. HRT indices and baroreflex sensitivity were analyzed from the ECGs and finger arterial pressure recordings during 30 minutes of spontaneous respiration in supine position. Beat-by-beat stroke volume and peripheral vascular resistance were computed by a nonlinear, self-adaptive model of aortic input impedance (Modelflow, Finapres Medical Systems, Arnhem, The Netherlands). Indices of HRT and baroreflex sensitivity were highly correlated. In patients with preserved LV function, there was no substantial dynamics of stroke volume in the late phase after VPC, while peripheral vascular resistance increased significantly. In patients with impaired LV function, potentiated first sinus beat after VPC triggered transient hemodynamic alternans. Dynamics of peripheral vascular resistance was attenuated and stroke volume was depressed in the late phase after VPC.

CONCLUSIONS

Delayed sympathetically mediated vasomotor response to VPC produces systolic blood pressure overshoot. This subsequently induces vagally mediated late heart rate deceleration. Under physiologic conditions, there is no evidence of other hemodynamic and/or mechanical effect outside the autonomic reflex arch. In patients with LV dysfunction, both depressed vagal and sympathetic modulation and, indirectly, enhanced postextrasystolic potentiation account for attenuated HRT.

The effects of altering time delays of coupled pacing during acute atrial fibrillation

BACKGROUND

Coupled pacing (CP), which consists of delivering a premature electrical stimulation to the heart after the effective refractory period of ventricular activation, is a novel method for controlling ventricular rate during atrial fibrillation (AF). It also has been established that CP improves pump function by enhancing external cardiac work and myocardial efficiency.

OBJECTIVE

The purpose of the present study was to determine if two time delays for CP (short and long) would result in similar improvements in ventricular function.

METHODS

In a canine model, we applied CP at two time delays (CP-S and CP-L) during two stages: sinus rhythm (SR) and acute AF. The cardiac responses to CP during SR served as the nontachycardic and nondepressed control. During both rhythms, we shortened the coupling interval until we obtained maximal contractility, designated CP-S. Next, we increased the delay until we started to see a measurable secondary contraction (left ventricular pressure development of approximately 20 mmHg). These longer delays were designated CP-L.

RESULTS

Our results showed that the ventricular rate of intrinsic activation (VRIA) remained decreased despite prolongation of the time delay of CP during both AF and SR. Also, both delays of CP increased left ventricular systolic pressure (LVSP) and dLVP/dt, which are indices of myocardial contractility. In contrast, CP increased external cardiac work only during AF. Prolonging this time delay did not markedly decrease the improvement in external cardiac work. Myocardial O(2) consumption (MVO(2)) did not significantly change as the result of CP during either SR or AF. Finally, myocardial efficiency improved during AF as the result of CP at both time delays.

CONCLUSIONS

In conclusion, shorter time delays for CP increased contractile strength during both SR and AF. However, extending the time delay of CP had minimal effects on diminishing the improved ventricular pump function and energetics that resulted from CP during AF. Thus, the maximal enhancement of myocardial contractility via CP-S was not needed to maintain the improved ventricular function during acute AF when CP is applied.

An efficient method for handling ectopic beats using the heart timing signal

The problem of analyzing heart rate variability in the presence of ectopic beats is revisited. Based on the integral pulse frequency modulation model and the closely related heart timing signal, a new technique is introduced which corrects for the occasional presence of ectopic beats. The correction technique, which involves the occurrence times of a certain number of beats preceding the ectopic beat, is computationally very efficient. From actual heart rate data, the results show that the new technique is associated with a much lower computational complexity (flops reduced by a factor of about 3000) than the original heart timing technique, while producing similar performance. It is also shown that the power spectrum and related clinical indices obtained by the new technique are more accurately estimated than by other methods.

Turbulence dynamics: An independent predictor of late mortality after acute myocardial infarction

INTRODUCTION

The prognostic value of heart rate turbulence for predicting mortality after acute myocardial infarction is well established. This study investigates a new measure of heart rate turbulence, termed turbulence dynamics, which quantifies the relationship between turbulence slope and underlying heart rate (HR(VPC)).

METHODS

Six hundred eight patients participating in the European Myocardial Infarction Amiodarone Trial had > or =25 ventricular premature complexes/24 h. During a follow-up period of 21 months (median), 120 patients died. Turbulence dynamics was assessed as the slope of the regression line between turbulence slope and HR(VPC). Survival analyses included age, history of previous myocardial infarction, presence of diabetes mellitus, mean normal-to-normal interval, heart rate variability index, presence of non-sustained ventricular tachycardia, left ventricular ejection fraction, turbulence onset and turbulence slope. All risk predictors were dichotomized at pre-defined cut-off points, turbulence dynamics was dichotomized at the median. Primary endpoint of the study was death of any cause.

RESULTS

In most patients, turbulence slope was inversely correlated to HR(VPC). Univariately, turbulence dynamics was the second strongest risk predictor of mortality (relative risk 2.4 (95% confidence interval 1.6-3.6), p<0.001). Multivariately, turbulence dynamics was the third strongest risk predictor (1.7 (1.1-2.7, p<0.01)).

CONCLUSION

In the patient population studied, turbulence dynamics was an independent predictor of mortality. The results indicate that in addition to the overall level of autonomic function the loss of autonomic adaptability contributes to prognosis.

Elimination of cardiac arrhythmias using oral taurine with l-arginine with case histories: Hypothesis for nitric oxide stabilization of the sinus node

We searched for nutrient deficiencies that could cause cardiac arrhythmias [premature atrial contractions (PACs), premature ventricular contractions (PVCs), atrial fibrillation, and related sinus pauses], and found literature support for deficiencies of taurine and l-arginine. Case histories of people with very frequent arrhythmias are presented showing 10-20g taurine per day reduced PACs by 50% and prevented all PVCs but did not prevent pauses. Adding 4-6g of l-arginine immediately terminated essentially all remaining pauses and PACs, maintaining normal cardiac rhythm with continued treatment. Effects of taurine useful in preventing arrhythmias include regulating potassium, calcium and sodium levels in the blood and tissues, regulating excitability of the myocardium, and protecting against free radicals damage. Taurine restored energy and endurance in one of the cases from a debilitated status to normal. Arrhythmias may also respond to taurine because it dampens activity of the sympathetic nervous system and dampens epinephrine release. l-arginine may have anti-arrhythmic properties resulting from its role as a nitric oxide (NO) precursor and from its ability to restore sinus rhythm spontaneously. Endogenous production of taurine and l-arginine may decline in aging perturbing cardiac rhythm, and these "conditional" essential nutrients therefore become "essential" and require supplementation to prevent morbidity and mortality. l-arginine is hypothesized to prevent cardiac arrhythmias by NO stabilization of the sinus node. Cardiac arrhythmias having no known cause in otherwise healthy people are hypothesized to be symptoms of deficiencies of taurine and arginine.

[Cardiac sympathetic innervation in patients with ventricular arrhythmias: an assessment by 123I-metaiodobenzylguanidine scintigraphy]

The aim of this study was to determine the state of sympathetic innervation in patients with ventricular arrhythmias (VA) using 123I-metaiodobenzylguanidine 123I -MIBG) scintigraphy. Fifty six patients (26 men and 30 women, mean age 37.4+/-11,6) underwent single-photon emission computed tomography (SPECT) imaging and planner scintigraphy after injection of 123I-MIBG (activity 148 MBq). They form three groups. Thirty patients with idiopathic VA (IVA) were included in group I: 14 patients with ventricular extrasystoles (VE) and 16 - with ventricular tachycardias (VT). Group II was formed by 17 patients (with dilated cardiomyopathy, n=7 and chronic myocarditis, n=10), 6 of them had VE and 11 - VT. The control group III was formed by 9 healthy subjects with structurally normal heart without VA. We analyzed early (30 minutes) and delayed (4 hours) images after 123I-MIBG administration. The global sympathetic activity (SA) was assessed by heart/mediastinum ratio and washout rate. Regional SA was assessed by extent and severity of defect. In group I 25 of 30 patients (83.3%) had regional SA abnormalities significantly different from controls (p<0.001). At the same time global uptake of 123I-MIBG in this group was not affected. In group II regional SA abnormalities were revealed in all patients (100%) and global reduction of 123I-MIBG uptake - in 14 patients (82.4%). Regional and global SA abnormalities in group II were different from controls (p<0.0001) and patients with IVA (p<0.001). There was no difference in SA abnormalities between patients with VE and VT. Our results suggest that patients with different VA have abnormalities of sympathetic innervation, including patients with structurally normal heart.

Longitudinal Age-Related Changes in 24-Hour Total Heart Beats and Premature Beats and Their Relationship in Healthy Elderly Subjects

The aim of this study was to conduct a longitudinal follow-up on age-related changes in 24-hour total heart beats (THBs) and total premature beats and their correlations in healthy elderly subjects. In 15 healthy elderly subjects (mean age, 70.0 +/- 4.1, age range at 1st recording, 64 to 80 years, 10 females, 5 males), we conducted Holter monitoring twice at an interval of 15 years and analysed age-related changes in THBs, atrial premature beats (APBs), and ventricular premature beats (VPBs), as well as their correlations. The results indicated that THBs, APBs, and VPBs all significantly increased with age in the healthy elderly subjects at a mean age of 70.0 +/- 4.1 (THB: 91074.1 +/- 11515.3 versus 99457.5 +/- 12131.0; P = 0.0004, APB:119.2 +/- 97.8 versus 884.4 +/- 1193.8; P = 0.0008, VPB: 15.2 +/- 53.6 versus 140.7 +/- 228.9; P = 0.0328). Moreover, we divided the subjects into increase and nonincrease groups based on the age-related changes in APB and VPB for 15 years ([n]; Inc-APB: Noninc-APB = 6 : 9, Inc-VPB: Noninc-VPB = 5 : 10). In the increase groups, premature beats tended to increase in proportion to changes in THBs with age (APB: Y = 207.488 + 0.136 X, r = 0.848, P = 0.0303; VPB: Y = -27.594 + 0.028 X, r = 0.727, P = 0.1921). In conclusion, this 15-year follow-up of Holter recordings in healthy elderly subjects revealed that THBs, APBs, and VPBs increased with age, and that the increases in premature beats, especially APBs, were in proportion to those in THBs.

Intracoronary infusion of Gd3+ into ischemic region does not suppress phase Ib ventricular arrhythmias after coronary occlusion in swine

Increased mechanical tension in the ischemic region during acute coronary occlusion might favor the occurrence of phase Ib ventricular arrhythmias. We aimed to investigate whether intracoronary administration of Gd(3+), a stretch-activated channel blocker, into the ischemic zone reduces the incidence of these arrhythmias. In thiopental-anesthetized, open-chest pigs, the left anterior descending coronary artery (LAD) was ligated for 45 or 48 min. Phosphate-free, HEPES-buffered saline bubbled with 100% N(2) was infused into the ischemic region for 4 min, starting 5 min (series A; n = 16) or 20 min (series B; n = 16) after coronary occlusion, at a rate doubling the baseline blood flow. Animals were blindly allocated to receive 40 muM Gd(3+) or only the buffer during the final 2 min of the infusion. There were no differences between groups with respect to hemodynamic variables, plasma K(+) levels, or size of the ischemic region. In neither series was the number of phase Ib premature ventricular beats reduced by Gd(3+) (46 +/- 20 in untreated vs. 91 +/- 37 in Gd(3+)-treated animals in series A and 19 +/- 7 vs. 22 +/- 13, respectively, in series B; both P = not significant). The occurrence of ventricular tachycardia or fibrillation was significantly associated with the magnitude of early ischemic expansion of the LAD region, as measured by ultrasonic crystals, but was also not prevented by Gd(3+). These results argue against a major role of stretch-activated channels inside the area at risk in the genesis of phase Ib ischemic ventricular arrhythmias.