We evaluated the effect of atrial overdrive on the incidence of atrial arrhythmias (AA) in 22 patients (67 +/- 9 years, 7 women, 15 men) with Chorus 6234 DDD pacemakers. Atrial overdrive was defined as a programmed paced rate 10 ppm faster than the mean ventricular rate stored for the last 24-hour period in the pacemaker memory. The protocol consisted of three phases of 1 month each. Phase I: observation after discontinuation of antiarrhythmic therapy. Phase II: arrhythmia analysis using the pacemaker memory after programming the lower rate to 55 ppm. The fallback function and histogram data were used to document the number and maximal duration of AA episodes as well as the total AA time in a month. Phase III: atrial overdrive. The mean ventricular heart rate was 65 +/- 4 beats/min before atrial overdrive versus 75 +/- 5 with atrial overdrive (P = 0.02). At the end of phase II, all patients presented with AA episodes (mean number per patient: 42 +/- 78 in one month). In phase III (with atrial overdrive), 14 (64.6%) patients had no recorded AA (group A). In the other eight patients with persistent AA episodes in phase III (group B), there was a significant reduction in the number of AA episodes (90 +/- 106 in phase II vs 38 +/- 87 in phase III; P = 0.01), their total duration (166 +/- 115 in phase II vs 92 +/- 134 hours in phase III; P = 0.03) and their maximal duration (121 +/- 103 in phase II vs 85 +/- 89 min; P = 0.04). Our short-term data suggest that atrial overdrive prevents or reduces AA episodes and demonstrate the feasibility and need of long-term studies to determine whether this benefit is sustained.
Automatic postventricular atrial refractory period (Auto-PVARP) is a dynamic interval designed to provide a longer PVARP at slower rates to enhance protection against pacemaker tachycardia (PMT) and a shorter PVARP to enhance atrial sensing at high rates. Auto-PVARP is often programmed in Medtronic devices for cardiac resynchronization therapy (CRT) with little knowledge of its intricate manifestations and disadvantages. The use of Auto-PVARP is contradictory to the universal teaching that CRT devices should be programmed with a short PVARP. We present the sequential ECGs of a patient with a CRT device programmed with Auto-PVARP in whom the atrial rate was increased with isoproterenol to simulate exercise. The recordings demonstrated that Auto-PVARP produced a substantial delay in the restoration of AV synchrony from the time the spontaneous atrial rate dropped below the programmed upper tracking rate. Auto-PVARP makes little sense (especially in the presence of first-degree AV block) in CRT patients considering that PMT is rare in this situation. In CRT patients, one should program a short and fixed PVARP of ≤ 250 ms.
Objective: To explore the application of a new 10 French intracardiac echocardiography (ICE) catheter with phased array and Doppler capable transducer for the assessment of epicardial and intramyocardial coronary blood flow. Methods: The coronary arteries were detected by cross sectional imaging in seven closed chest dogs, and coronary blood flow visualised by colour Doppler. Blood flow velocities were recorded by pulsed Doppler at baseline for reproducibility of repeated measurements, and during hyperaemia for coronary flow reserve measurements. Comparisons were made with Doppler guide wire data obtained simultaneously. Intramyocardial coronary artery blood flow was assessed by colour flow mapping, and the blood flow velocities recorded using pulsed Doppler at baseline and during hyperaemia. Results: Seven left main, six left anterior descending, seven left circumflex, and five right coronary arteries were visualised in the seven animals by cross sectional or colour Doppler imaging. Repeated measurements of coronary flow velocity showed a good correlation (mean diastolic velocity, r = 0.93, n = 22, p < 0.0001; peak diastolic velocity, r = 0.96, n = 22, p < 0.0001, respectively). Intraobserver/interobserver variability was satisfactorily low. Coronary flow reserve from ICE correlated highly with the value obtained from the Doppler guide wire (r = 0.90, n = 26, p < 0.0001). Intramyocardial coronary blood flow was identified in all seven dogs, and flow velocities were recorded at baseline and during hyperaemia in four animals. Conclusions: This new ICE catheter provides high quality diagnostic resolution. It is useful for coronary blood flow assessment.
A fast ventricular tachycardia was apparently induced in a patient with a CRT-D device by the delivery of a pacemaker stimulus whose timing corresponded with the timing of the QRS complex in the far-field electrogram. Appropriate programming of the device might have prevented this complication.
Case PresentationThe BCG of a 60-year-old man with a dilated cardiomyopathy and normal coronary arteries showed nonnal sinus rhythm and PR intervals and intermittent complete left bundle branch block (LBBB). Figure 1 shows the baseline 12-lead E^G where the relatively narrow QRS complex (0.08 sec) probably represents a minor degree of incomplete LBBB associated with left ventricular Figure 1. Twelve-lead ECG showing a tiny q in aVL The QRS measures 0.08 .second.^, and the pattem is compatible with a minor degree of incomplete teft bundte hranch btoctcand left ventricular hypertrophy.
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