Sinus node dysfunction and impairment of global atrial conduction time after high rate atrial and ventricular pacing in dogs.

It has been shown in animals and humans that AF shortens the atrial refractory period and impairs its rate adaptation. The aim of the study was to evaluate the effects of high rate pacing on sinus node function and intraatrial conduction. Eight dogs were subjected to rapid atrial pacing (AP) at a rate of 400 beats/min for 16 days. After a complete recovery of left ventricular function, they underwent rapid ventricular pacing (VP) at 240 beats/min of equal duration. Sinus node recovery time (SNRT) was measured after pacing at 150, 160, and 170 beats/min. P wave duration was measured on a surface ECG recorded at a paper speed of 200 mm/s. Measurements were performed at baseline, immediately after AP or VP, and four weeks after termination of AP or VP. SNRT immediately after AP and VP was significantly prolonged at all three pacing rates (P < 0.03). P wave duration increased significantly after either type of pacing (AP: 74.3 +/- 6.4 ms, VP: 70.0 +/- 3.8 ms) compared with baseline values (60.6 +/- 6.2 ms, P < 0.05). Rapid AP and VP induces sinus node dysfunction and prolongs intraatrial conduction time. The effects of sustained AP and VP on sinus node function and atrial myocardium returned toward control values 4 weeks after cessation of pacing. The authors hypothesize that reversible electrical remodeling occurs both in the sinus node and in the atrial myocardium.

Left atrial systolic function in relation to electrical and mechanical remodeling in a canine model.

Rapid atrial activation causes electrical remodeling that promotes the occurrence and maintenance of atrial fibrillation. The aim of this research was to compare the relationship between mechanical remodeling and atrial electrophysiology. Eight dogs (beagles) were subjected to rapid atrial pacing (AP) at 400 beats/min for 16 days. After a complete recovery of electrical variables and left ventricular function evaluated by echocardiography, they underwent high-rate ventricular pacing (VP) at 240 beats/min of equal duration. In half of them, the study was started by VP and in the other half by AP. Left atrial systolic function was assessed by transesophageal echocardiography. Atrial effective refractory period (AERP) at a basic cycle length of 400 ms decreased significantly after either type of pacing (AP: 115 +/- 17 ms, VP: 136 +/- 22 ms) compared with baseline values (153 +/- 23 ms); the difference between tachycardias was significant too (p < 0.02). Significant increases (p < 0.05) in left atrial dimensions (LA-A) (AP: 2.41 +/- 0.23 cm ,VP: 2. 43 +/- 0. 34 cm vs. basal: 2. 16 +/- 0. 21 cm) indicated atrial dilatation after either type of pacing, the differences between two groups being insignificant. Atrial reversal pulmonary venous flow (AR velocity) decreased in AP (-0.13 +/- 0. 02 m/s) and VP (-0. 17 +/- 0. 04 m/s). The difference was highly significant as compared to basal values (-0.25 +/- 0.05 m/s) and also with respect to both tachycardias (p < 0.01). In both groups, atrial remodeling occurred in a relatively short period of time. The echocardiographic findings suggested that left atrial systolic function was significantly more disturbed in the AP group than in the VP group. Mechanical changes are an important substrate of electrical remodeling, yet the deterioration of electrical variables was more pronounced in AP than in VP.

Rabies surveillance and control measures in Slovenia.

The article briefly describes the sylvatic rabies situation in Slovenia in the period from 1980 to 2000, the reasons for the replacement of manual distribution of baits by aircraft distribution. An overview of the control measures, surveillance system and control programs is given.

Tachycardia induced cardiomyopathy in dogs; relation between chronic supraventricular and chronic ventricular tachycardia.

Long-standing ventricular tachycardia (VT) and supraventricular tachycardia (SVT) can produce a reversible left ventricular dysfunction. The onset of cardiomyopathy and the severity of posttachycardic changes depend at least on three parameters of tachycardia, including its type (VT or SVT), rate and duration. Ten dogs (beagles) were paced at 180 beats/min for 3 weeks. Two pacing modalities, supraventricular and ventricular, were used in each dog. In half of them, the study was started by ventricular, and in the other half by supraventricular high-rate pacing. The alternate pacing modality was applied after complete recovery of left ventricular function. Ventricular function and morphology were evaluated by radionuclide ventriculography, echocardiography and Swan-Ganz catheterisation. Posttachycardic changes were studied in sinus rhythm after cessation of pacing. Left ventricular ejection fraction (LVEF) fell significantly after either type of tachycardia (SVT: 53 +/- 5%, VT: 48 +/- 7%, P < 0.05) compared with baseline values (69.5 +/- 2.3%). Significant increases (P < 0.05) in end-systolic (SVT: 2.1 +/- 0.3 cm, VT: 2.4 +/- 0.2 cm vs. 1.6 +/- 0.3 cm) and end-diastolic dimensions (SVT: 3.0 +/- 0.3 cm, VT: 3.3 +/- 0.4 cm vs. 2.7 +/- 0.3 cm) indicated ventricular dilation in paced animals. Left ventricular pulmonary capillary wedge pressure increased significantly after either type of tachycardia as compared with baseline values (SVT: 7.5 +/- 1.2 mmHg, VT: 8.4 +/- 1.1 mmHg vs. 1.9 +/- 1.5 mmHg, P < 0.05); the difference between tachycardias was not significant. The present study demonstrates that chronic SVT and VT result in left ventricular dysfunction in a relatively short time, even if the heart rate is not very high. Deterioration of left ventricular ejection fraction and dilation of the left ventricle are more marked in chronic VT than in chronic SVT.

Cardiac involvement in Emery-Dreifuss muscular dystrophy: role of a diagnostic pacemaker.

Emery-Dreifuss muscular dystrophy is an X-linked recessive myopathy. Its progression is slow, and it rarely leads to cessation of walking; therefore, it has often been called "benign." On the other hand, cardiac involvement is often severe and sudden death is not uncommon. We describe a family with four affected males, two of whom died suddenly. The case of an affected man with first-degree AV block, incomplete right bundle branch block, and left anterior fascicular block is described in detail. The prophylactic insertion of a diagnostic pacemaker enabled us to follow the progress of conduction disturbances without leaving the patient unprotected. While AV and intraventricular conduction defects were more prominent before pacemaker implantation, sinus node dysfunction became more important during the follow-up.

Complete cure after a seemingly unsuccessful operation for Wolff-Parkinson-White syndrome.

A 48-year-old man with Wolff-Parkinson-White syndrome and poorly tolerated atrial fibrillation underwent surgical dissection of an accessory pathway. After operation electrocardiogram revealed a very unfavorable outcome: sinus rhythm with persistence of delta waves alternated with sequences of complete atrioventricular block. Therefore, an early reoperation was planned. Fortunately, in the next days conduction through the accessory pathway and signs of atrioventricular block disappeared. Complete cure was observed during long-term follow-up.