True bipolar and integrated bipolar sensing and detection by implantable defibrillators.

INTRODUCTION: Sensing and detection can be performed in true bipolar or integrated bipolar configuration by implantable defibrillators. New Medtronic generators (Medtronic Inc., Minneapolis, MN, USA) can be configured so that the sensing function of the device can be either true bipolar or integrated bipolar. We compared the sinus rhythm R-wave amplitude and detection time of induced ventricular fibrillation (VF) at implant (acute phase), and sinus rhythm R-wave amplitude 3 months or more after the implant (chronic phase) in these two configurations. METHODS: Twenty-eight patients were studied in the acute phase, and a subgroup of 15 patients was tested in the chronic phase. The generators were Medtronic model numbers D224VRC, D224TRK, D224DRG, D284VRC, D284TRK, and D284DRG. The leads were Medtronic 6947 or 6935. Sensing was evaluated by recording the electrogram and measuring the R-wave peak-to-peak amplitude in the two configurations. Detection was evaluated by measuring the detection time in the two configurations in two consecutive inductions. The detection time was measured on programmer paper from the marker of the T shock to the marker of VF. RESULTS: The acute-phase values were: R wave in true bipolar configuration 13.9 ± 7.1 mV, R wave in integrated bipolar configuration 13.6 ± 6.9 mV (p = 0.38),VF detection time in true bipolar configuration 3.12 ± 0.39 seconds, and VF detection time in integrated bipolar configuration 3.17 ± 0.39 seconds (p = 0.52). CONCLUSIONS: Sensing and detection at implant were not significantly different between the true bipolar and the integrated bipolar configurations for the tested leads and generators.

Strength duration curve for left ventricular epicardial stimulation in patients undergoing cardiac resynchronization therapy.

INTRODUCTION: The strength duration curve has been studied for right ventricular endocardial stimulation. There are differences between left ventricular epicardial and right ventricular endocardial stimulation due to different electrophysiologic properties and different electrode-tissue interface. The strength duration curve for epicardial left ventricular stimulation has not been studied so far. METHODS: One hundred and three patients were studied. The strength duration curves were determined for left ventricular epicardial and right ventricular endocardial stimulation. The studied points were chronaxie, rheobase, and voltage threshold at 0.5 ms. Left ventricular leads Guidant 4512, 4513, 4537, 4538 (unipolar, area 3.5 mm(2); Guidant Corp., St. Paul, MN, USA), Medtronic 4193 (unipolar, area 5.8 mm(2); Medtronic Inc., Minneapolis, MN, USA), Guidant 4518, 4542, 4543 (bipolar, area 4 mm(2)), St. Jude Medical (bipolar, area 4.8 mm(2); St. Jude Medical, St. Paul, MN, USA), and Medtronic 4194 (bipolar, area 5.8 mm(2)) were studied. RESULTS: The Guidant unipolar leads with a distal electrode area of 3.5 mm(2) had a lower chronaxie than the other studied leads. The left ventricular epicardial and right ventricular endocardial chronaxie for 15 patients with Medtronic left ventricular leads 4194 or 4193 (5.8 mm(2)) and right ventricular leads 6947 (5.7 mm(2)) were 0.52 +/- 0.36 ms and 0.62 +/- 0.46 ms (P > 0.05). CONCLUSION: The left ventricular epicardial chronaxie depends on the lead. The left ventricular epicardial chronaxie is similar to the right ventricular endocardial chronaxie for leads with similar electrode stimulation area.

Current concepts and management strategies in atrial flutter.

After atrial fibrillation, atrial flutter (AFL) is the most important and most common atrial tachyarrhythmia. Atrial flutter describes an electrocardiographic model of atrial tachycardia >or=240/min, with a uniform and regular continuous wave-form. There is classically a 2:1 conduction across the atrioventricular (AV) node; as a result, the ventricular rate is usually one-half the flutter rate in the absence of AV node dysfunction. AFL can be harmful by impairing the cardiac output and by encouraging atrial thrombus formation that can lead to systemic embolization. There are four major concerns that must be addressed in the treatment of AFL: reversion to normal sinus rhythm (NSR); maintenance of NSR; control of the ventricular rate; and prevention of systemic embolization. Our review will highlight strategies for reverting patients back to NSR and then maintaining them in NSR, with emphasis on the recent updates, including the role of ablation in the management of atrial flutter.

Strength duration curve for epicardial left ventricular stimulation.

BACKGROUND: The strength duration curve for endocardial stimulation has been extensively studied. Little information is available on the left ventricular epicardial strength duration curve. In view of the large number of patients treated with resynchronization therapy, left ventricular epicardial stimulation parameters have practical importance. METHODS: Twelve patients who underwent implant of a biventricular defibrillator were available for at least 4 months of follow up and accurate determination of strength duration curves were studied. Strength duration curves were constructed at 30 days (subacute phase) and 4 or more months (chronic phase) after the implant for right ventricular endocardial, left ventricular epicardial unipolar, and left ventricular bipolar stimulation. The goal was to determine the chronaxie, which correlates with the most economical stimulation. RESULTS: There was no significant difference between the right ventricular endocardial and left ventricular epicardial bipolar chronaxie (P = 0.57 subacute and 0.6 chronic) or right ventricular endocardial and left ventricular unipolar chronaxie (P = 0.93 subacute and 0.92 chronic). Most chronaxie values were lower than the factory default values. CONCLUSION: The left ventricular unipolar or bipolar epicardial chronaxie is not significantly different from the right ventricular endocardial chronaxie. Both values are lower than the pulse duration used as default setting in most devices as well as in clinical practice. Individual determination of the chronaxie could lead to energy savings.

T wave oversensing in implantable cardioverter defibrillators.

The implantable cardioverter defibrillator is the treatment of choice for patients with ventricular tachycardia, especially in the setting of structural heart disease, but inappropriate therapy continues to be a problem. In this report we describe a short case series of patients who presented with T wave oversensing. We propose a classification in 2 categories, T wave oversensing occuring in the setting of persistently low R wave amplitude, and T wave oversensing occuring in the setting of transiently low R wave amplitude.

Radiofrequency catheter ablation using non-contact mapping for inappropriate sinus tachycardia.

INTRODUCTION: In this report we describe our experience using non-contact mapping for radiofrequency ablation in patients with inappropriate sinus tachycardia. METHODS AND RESULTS: Two female patients with persistent complaints of palpitations and documented inappropriate sinus tachycardia with failed medical management underwent radiofrequency ablation using non-contact mapping. Non-contact mapping provided a continuous determination of the site of earliest breakthrough, facilitating the delivery and the assessment of the results of each radiofrequency application. CONCLUSION: Non-contact mapping is an effective mapping modality in the interventional treatment of inappropriate sinus tachycardia.