Implantation of a dual-chamber, rate-adaptive pacemaker in a horse with suspected sick sinus syndrome

A five-year-old gelding suffered syncope at the end of a period of exercise. A 24-hour electrocardiogram recording revealed intermittent pauses in the sinus rhythm of up to 10 seconds, indicating sinus node disease; the pauses occurred repeatedly, particularly after exercise. A dual-chamber, rate-adaptive pacemaker was successfully implanted, which prevented excessive postexercise bradycardia and syncope, and allowed the horse to return to work.

An equine model of chronic atrial fibrillation: methodology

We describe the development and the different features of an experimental model of chronic atrial fibrillation (AF) in equines. In four healthy ponies a dual-chamber pacemaker, with an adapted pacemaker program, was implanted transvenously in the standing animal. This adapted pacemaker induced episodes of AF by delivering a 2s burst of electrical stimuli (42 Hz) as soon as sinus rhythm was detected. Simultaneous with a surface electrocardiogram, the intra-atrial electrogram could be recorded to determine the atrial electrogram morphology. Programmed electrical stimulation (PES) was used to determine the atrial effective refractory period (AERP) and the rate adaptation of the AERP, the sinus node recovery time (SNRT) and the corrected SNRT, AF vulnerability, AF cycle length and AF duration. This experimental AF model can be used to study the pathophysiology of chronic AF in equines.

Dual-chamber pacemaker implantation via the cephalic vein in healthy equids

The purpose of the present study was to develop a feasible and safe technique for dual-chamber pacemaker implantation in healthy horses. Implantation was performed in a standing, tranquilized horse and in ponies. Atrial and ventricular leads were transvenously inserted through the cephalic vein, and a subcutaneous pacemaker pocket was created between the lateral pectoral groove and the manubrium sterni in 6 equids. Positioning of each lead was guided by echocardiography and by measuring the electrical characteristics of the lead. The implantation procedure lasted about 4 hours in each animal and was well tolerated. In all animals, dual-chamber pacemaker function was obtained, and these results remained good throughout the follow-up period. At the time of implantation, atrial and ventricular sensing were between 2.1 and 7.2 mV and 7.8 and 16.8 mV, respectively, and atrial and ventricular pacing thresholds at 0.5 millisecond varied from 0.5 to 0.7 V and from 0.3 to 1.0 V, respectively. Six months after the implantation, sensing values varied from 2 to 10 mV for the atrial lead and from 2 to 16 mV for the ventricular lead, while pacing thresholds at 0.5 millisecond varied from less than 0.5 to 2.5 V for the right atrium and from less than 0.5 to 5.0 V for the right ventricle. Atrial lead dislodgment occurred in 2 animals, requiring insertion of a new lead. Ventricular lead dislodgment was not observed.

Long term results of cardioverter-defibrillator implantation in patients with right ventricular dysplasia and malignant ventricular tachyarrhythmias

OBJECTIVE

To study the outcome of patients with arrhythmogenic right ventricular dysplasia treated with an implantable cardioverter-defibrillator (ICD) for ventricular tachyarrhythmias complicated by haemodynamic collapse.

DESIGN

Observational study.

SETTING

University hospital.

PATIENTS

Nine consecutive patients (eight male, one female; mean (SD) age, 36 (18) years) with arrhythmogenic right ventricular dysplasia presenting with ventricular tachycardia and haemodynamic collapse (n = 6) or ventricular fibrillation (n = 3), treated with an ICD.

MAIN OUTCOME MEASURES

Survival; numbers of and reasons for appropriate and inappropriate ICD interventions.

RESULTS

After a mean (SD) follow up of 32 (24) months, all patients were alive. Six patients received a median of 19 (range 2-306) appropriate ICD interventions for events detected in the ventricular tachycardia window; four received a median of 2 (range 1-19) appropriate ICD interventions for events detected in the ventricular fibrillation window. Inappropriate interventions were seen for sinus tachycardia (18 episodes in three patients), atrial fibrillation (three episodes in one patient), and for non-sustained polymorphic ventricular tachycardia (one episode in one patient).

CONCLUSIONS

Patients with arrhythmogenic right ventricular dysplasia and malignant ventricular arrhythmias have a high recurrence rate requiring appropriate ICD interventions, but they also often have inappropriate interventions. Programming the device is difficult because this population develops supraventricular and ventricular tachyarrhythmias with similar rates.

Factors determining long-term outcomes and survival in patients with coronary artery disease and ventricular tachyarrhythmias: a single center experience

A Single-Center Experience. The influence, after ICD implantation, of concomitant CABG, angioplasty, and other antiischemic therapeutic interventions, like treatment with beta-blockers, on outcome and mortality of patients with VT or VF due to CAD remains uncertain. The univariate and multivariate risks of recurrence of ventricular arrhythmias requiring ICD interventions or death associated with baseline clinical and functional variables were studied in 160 consecutive patients with CAD of whom 30 underwent CABG or angioplasty at < or = 2 weeks before ICD implantation. ICD interventions occurred in 98 (61%) patients over a mean follow-up of 1,065 days. In univariate and multivariate analysis, VT as the presenting arrhythmia was the only clinical factor predictive of recurrences. Treatment with beta-blockers at hospital discharge reduced the probability of recurrences. Kaplan-Meier analysis confirmed the effect of beta-blockers (P < 0.005) and of VT as the presenting arrhythmia (P < 0.01). Overall mortality was 61% (29/160). In multivariate analysis a low ejection fraction (< or = 0.20) and omission of angiotensin-converting enzyme inhibitors at discharge were associated with excess mortality. In Kaplan-Meier analysis, a low ejection fraction (borderline between 0.30 and 0.21, significant < 0.21) was the single predictor of mortality. Revascularization by CABG or angioplasty had no influence on ventricular arrhythmia recurrences or survival. During long-term follow-up, VT as the presenting arrhythmia and the omission of beta-blocker therapy were associated with excess recurrences of ventricular arrhythmias after ICD implantation. In contrast, survival depended primarily on left ventricular function at discharge. Revascularization did not prevent recurrences of arrhythmias and had no significant effect on survival in the small group of patients who underwent CABG or angioplasty.

Prevalence of potential candidates for biventricular pacing among patients with known coronary artery disease: a prospective registry from a single center

New forms of ventricular pacing are increasingly studied as an option in the management of patients with heart failure. Coronary artery disease (CAD) is the most frequent cause of heart failure, and patients with complete left or right bundle branch block (LBBB and RBBB) and a reduced left ventricular ejection fraction (LVEF) are the best candidates for this new therapy. However, the prevalence of this clinical presentation is uncertain. During a 1-year period, 433 patients with documented CAD (mean age 64 +/- 10 years, 79% men) who were referred for myocardial perfusion imaging were prospectively studied. All patients underwent a 2-day stress-rest gated 99mTc-Tetrofosmin SPECT study with evaluation of resting LV enddiastolic (LVEDV) and endsystolic (LVESV) volumes and LVEF. The resting ECG was examined in all patients for the presence of complete LBBB or RBBB. Of the 433 patients with CAD 36 patients (8.3%) had LBBB (n = 14) or RBBB (n = 22) and a QRS width > 120 ms. These 36 patients were in general older and more frequently had diabetes and atrial fibrillation. Patients with LBBB or RBBB had a significantly lower LVEF (41 +/- 16% vs 48 +/- 14%, P < 0.01) and significantly higher LV volumes compared to patients without LBBB or RBBB (177 +/- 79 mL vs 131 +/- 53 mL, P < 0.001 for LVEDV and 116 +/- 76 mL vs 73 +/- 49 mL, P < 0.001 for LVESV). In total, 112/433 (26%) had an LVEF < or = 40%; 16 had also a LBBB or RBBB (3.7% of the whole population, 14% of the patients with a LVEF < or = 40%). Within the group of patients with a LVEF > or = 40%, patients with BBB had comparable LVEF (26 +/- 9% vs 30 +/- 8%, P = NS) but significantly higher LVEDV and LVESV (230 +/- 70 mL vs 190 +/- 64 mL, P < 0.05 for LVEDV and 170 +/- 65 mL vs 135 +/- 56 mL, P < 0.05 for LVESV). In this prospective registry 3.7% of all patients with known CAD had LBBB or RBBB in combination with a LVEF < or = 40%. This represented 14% of all patients with a LVEF > or = 40%. These limited numbers should be kept in mind when considering biventricular pacing as a new therapeutic options in patients with heart failure.

Pacing induced sustained atrial fibrillation in a pony

A transvenous, screw-in electrode was implanted in the right atrium of a healthy pony and connected with an implantable pulse generator programmed to deliver bursts of electrical stimuli to the atrium. Initially, cessation of burst pacing resulted in short (less than 1 minute), self-terminating episodes of atrial fibrillation. As burst pacing continued, the episodes of induced atrial fibrillation became longer. After 3 weeks of continuous atrial pacing, atrial fibrillation became sustained (56 hours). This model of pacing induced atrial fibrillation can be used to study the mechanisms leading to atrial fibrillation, its perpetuation and therapy. Our preliminary observations support the concept that once atrial fibrillation starts, it sets up changes in the electrical characteristics of the atrium that favor its own perpetuation.

Use of an implantable cardioverter defibrillator in a patient with two implanted neurostimulators for severe Parkinson's disease

We report a patient with Parkinson's disease treated with two pectorally implanted neurostimulators (NSs) who presented with a life-threatening ventricular tachyarrhythmia in whom an abdominal ICD was implanted. Testing during implantation showed that the NS did not affect the bipolar sensing of the ICD, even when the NSs were set at a frequency of 130 pulses/s with an output of 5 V and pulse width of 0.21 ms in a bipolar and a unipolar configuration. The ICD shock, however, did affect both NSs: there was a reset to the output Off state and there was a reset of the electrode polarities.

Trends in the prevalence, detection, treatment and control of arterial hypertension in the Belgian adult population

OBJECTIVES

To discuss changes during the past decades in the prevalence and in the patterns of detection, treatment and control of arterial hypertension in the general Belgian population aged 25-64 years.

DESIGN

Data from two cross-sectional cardiovascular disease risk factor surveys of the general population aged 25-64 years during the first and second halves of the 1980s (the Belgian Inter-university Research on Nutrition and Health study of 1980-1984 and the World Health Organization Multinational Monitoring of Trends and Determinants in Cardiovascular Diseases study of 1985-1992) are compared.

PARTICIPANTS

Age-stratified and sex-stratified random samples from the general population yielded 9372 participants in the former study and 4904 participants in the latter.

METHODS

In both studies, blood pressure measurements and other variables were collected in the same standardized way and by the same observers.

RESULTS

For both sexes, overall age-standardized prevalences of hypertension (subjects with systolic blood pressure > or = 160 mmHg or diastolic blood pressure > or = 95 mmHg or currently being administered antihypertensive drug treatment) were found to be significantly (P< 0.001) higher in the former than they were in the latter study. A significant decline in population mean systolic blood pressure values was observed for both sexes on going from the former data to the latter (falls of 6.0 and 7.3 mmHg for men and women, respectively, P< 0.01). In log-linear models, adjusted for age, a highly significant (P< 0.0001) favourable shift in the population distribution over the various categories of detection, treatment and control of hypertension was observed. This trend exhibited a significant sex difference, however, there being a much more favourable trend for women.

CONCLUSIONS

In Belgium, favourable trends in the prevalence and in the patterns of detection, treatment and control of arterial hypertension and in the levels of systolic blood pressure were observed. The so-called 'rule of halves' is no longer valid.

Atrial flutter with 1:1 conduction after administration of the antimalarial drug mefloquine

Antimalarial drugs are well known for their cardiovascular toxicity. Quinine, the most famous antimalarial agent, mostly causes bradycardia. Quinidine, its dextrorotatory isomer, may cause 1:1 atrioventricular (AV) conduction during atrial flutter. The newly developed drug mefloquine was reported to have fewer cardiac side effects. We describe a 63-year-old male patient with atrial flutter in whom mefloquine use was associated with 1:1 AV conduction, and who then responded to therapy with digoxin and sotalol. The patient had a history of palpitations. This case report emphasizes that mefloquine should be used with caution in patients with a history of palpitations or underlying heart disease.