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Dipen Shah

Publications and source records attributed to Dipen Shah.

At least 19 recordsLinked to original sources
PubMed2006

Utility of the surface ECG before VDD pacemaker implantation.

BACKGROUND: VDD pacemakers may be implanted in the setting of atrioventricular block with preserved sinus function. Their main advantage over DDD pacemakers is use of a single lead. However, low-amplitude atrial electrograms (EGMs) recorded from the free-floating atrial electrode may lead to undersensing. There is currently no way of predicting EGM amplitude prior to implantation and to thus identify candidates who may be safely implanted with a VDD pacemaker. AIM: We sought to investigate whether the P-wave amplitude measured on the standard surface ECG correlates with the atrial EGM amplitude measured by the single-pass lead at implantation. METHODS: Data on 122 patients implanted with a VDD pacemaker at our institution were reviewed. Atrial EGM amplitudes measured at implantation by the single-pass lead were correlated with the maximal P-wave amplitude on the surface ECG recorded just prior to implantation. RESULTS: There was a highly significant correlation between the maximal P-wave amplitude on the surface ECG and the atrial EGM (Pearson's correlation 0.313, P<0.001). Multivariate analysis showed that maximal P-wave amplitude was independently associated with atrial EGM amplitude (p=0.003). For the overall population, an EGM amplitude of <0.9 mV was present in only 11/122 (9%) cases. An atrial EGM amplitude of <0.9 mV was found in 10/69 (14%) of patients with a maximal surface P-wave < or =0.1 mV but only in 1/53 (2%) of those with >0.1 mV (p=0.023). CONCLUSION: Low-amplitude atrial EGMs at implantation are found in a minority of patients with single-pass leads. However, patients with a maximal surface P-wave amplitude of >0.1 mV are especially unlikely to have a low atrial EGM amplitude and may be good candidates for a VDD pacemaker.

Aged↗
PubMed2006

Drug-induced long QT syndrome in injection drug users receiving methadone: high frequency in hospitalized patients and risk factors.

BACKGROUND: Drug-induced long QT syndrome is a serious adverse drug reaction. Methadone prolongs the QT interval in vitro in a dose-dependent manner. In the inpatient setting, the frequency of QT interval prolongation with methadone treatment, its dose dependence, and the importance of cofactors such as drug-drug interactions remain unknown. METHODS: We performed a systematic, retrospective study comparing active or former intravenous drug users receiving methadone and those not receiving methadone among all patients hospitalized over a 5-year period in a tertiary care hospital. A total of 167 patients receiving methadone fulfilled the inclusion criteria and were compared with a control group of 80 injection drug users not receiving methadone. In addition to methadone dose, 15 demographic, biological, and pharmacological variables were considered as potential risk factors for QT prolongation. RESULTS: Among 167 methadone maintenance patients, the prevalence of QTc prolongation to 0.50 second((1/2)) or longer was 16.2% compared with 0% in 80 control subjects. Six patients (3.6%) in the methadone group presented torsades de pointes. QTc length was weakly but significantly associated with methadone daily dose (Spearman rank correlation coefficient, 0.20; P<.01). Multivariate regression analysis allowed attribution of 31.8% of QTc variability to methadone dose, cytochrome P-450 3A4 drug-drug interactions, hypokalemia, and altered liver function. CONCLUSIONS: QT interval prolongation in methadone maintenance patients hospitalized in a tertiary care center is a frequent finding. Methadone dose, presence of cytochrome P-450 3A4 inhibitors, potassium level, and liver function contribute to QT prolongation. Long QT syndrome can occur with low doses of methadone.

Adolescent↗
PubMed2006

[Radiofrequency ablation in ventricular tachycardia: an alternative to implanted cardioverter defibrillator?].

Patients with ventricular tachycardia (VT) are subject to frequent recurrences despite antiarrhythmic drug therapy. Radiofrequency ablation is a useful alternative. Implantable defibrillators terminate episodes of VT but do not prevent them. The efficacy of catheter ablation depends on the cause and location of VT. There are two situations: VT in patients without identifiable structural heart disease or idiopathic VT and VT related to structural heart disease. After catheter ablation, idiopathic VT has a good prognosis and implantable defibrillators are usually not indicated. Scar-related VT are more difficult to treat with catheter ablation, but this technique is particularly useful for controlling frequent defibrillator shocks and incessant VT.

Catheter Ablation↗
PubMed2006

Identifying far-field superior vena cava potentials within the right superior pulmonary vein.

BACKGROUND: Far-field extra-pulmonary vein (PV) potentials originating from the left atrial appendage and adjacent left atrium have been identified within the left PVs, but no systematic study of extra-PV potentials within the right superior PV (RSPV) has been described. OBJECTIVES: The purpose of this study was to prospectively analyze extra-PV contributions to RSPV potentials. METHODS: In a consecutive, prospective series of 114 patients (96 men and 18 women; 56 +/- 10 years) undergoing electrophysiologically guided ostial PV isolation, residual potentials recorded with a circular mapping catheter in the RSPV after ostial isolation were analyzed. Their extra-PV origin was validated by mapping a site with identical timing (in sinus rhythm or atrial fibrillation) within the adjacent superior vena cava (SVC) where, in sinus rhythm, local pacing (until threshold amplitude) concealed the residual potential within the stimulus artifact because of very short activation timing. The timing of residual potentials with respect to surface ECG P-wave onset was measured and compared with the earliest timing of ablated RSPV potentials. RESULTS: Residual low-amplitude (mean 0.29 +/- 0.17 mV, range 0.07-0.65 mV) extra-PV potentials were recorded from the anterior and superior aspect of the RSPV in 3.6 +/- 1 bipoles in 26 (23%) patients (all men, 51 +/- 10 years) with a timing from sinus P-wave onset of 17 +/- 12 ms (range 0-40 ms) vs 52 +/- 9 ms (range 35-70 ms) for the earliest RSPV potential (P <.001, t-test). Extra-PV potentials all originated from the posterior aspect of the SVC. The SVC potential was identified during ongoing atrial fibrillation in eight patients and later confirmed in sinus rhythm. An extra-PV potential of SVC origin could be identified by timing earlier than 30 ms from onset of the sinus P wave, with sensitivity of 92%, specificity 100%, positive predictive value 100%, and negative predictive value 89%. CONCLUSION: Extra-PV potentials of right-sided SVC origin were recorded within the RSPV in 23% of patients and can be identified with high sensitivity and specificity by a timing within 30 ms of sinus P-wave onset. Recognizing these potentials can avoid unnecessary additional ablation and possibly PV stenosis or phrenic paralysis.

Adult↗
PubMed2006

Simulation of anteroseptal myocardial infarction by electrocardiographic filters.

BACKGROUND: Most electrocardiographs have high-pass filters that may be used to attenuate baseline wander due to respiratory artifact. However, the T wave also has low-frequency components and may be distorted by these filters. Our aim was to investigate the effect of high-pass filters on the ST segment. METHODS: Twenty healthy volunteers had a standard 12-lead electrocardiogram recorded using a Bard EP Labsystem (Bard Inc, Lowell, Mass) at different high-pass filter settings (0.05, 0.1, 0.5, and 1.0 Hz). ST-segment elevation or depression was measured using digital calipers at each setting and the electrocardiogram classified as being either normal or suggestive of myocardial infarction. RESULTS: There were no significant differences in ST elevation between 0.05- and 0.1-Hz filter settings. However, at 0.5 and 1.0 Hz, there was significant ST elevation in the right precordial leads and ST depression in the inferior leads. The greatest changes were observed in V2, with an ST elevation of 0.13 +/- 0.08 and 0.18 +/- 0.09 mV at 0.5 and 1.0 Hz, respectively (P < .0001 compared with 0.05 Hz). All tracings were considered normal at 0.05- and 0.1-Hz filter settings. However, at 0.5 and 1.0 Hz, 60% and 100%, respectively, of tracings were suggestive of anteroseptal myocardial infarction. Signal distortion was attributed to phase nonlinearities of the filters. CONCLUSIONS: High-pass filters may distort the ST segment and simulate anteroseptal myocardial infarction. These filters should comply with current standards if used on electrocardiographs and be used with caution. In case of doubt, the tracings should be compared with minimally filtered recordings.

Adult↗
PubMed2006

Optimization of device programming for cardiac resynchronization therapy.

Cardiac resynchronization therapy may lead to remarkable improvement in clinical status in selected patients with heart failure. However, approximately 20-30% of patients may not respond to this treatment. One of the reasons for this may be suboptimal programming of the device, which has particular considerations as compared to standard pacemakers. Hemodynamic response to pacing may be affected by timing of the atrioventricular (AV) interval, affecting synchronicity of atrial and ventricular contraction. In addition current biventricular devices have separate right and left ventricular channels that allow programming of an interventricular (VV) interval with right or left ventricular preexcitation. This article focuses on the parameters that may be optimized for biventricular pacing, and reviews the different techniques currently available for this application, with special emphasis paid to echocardiography.

Algorithms↗
PubMed2006

Narrow, slow-conducting isthmus dependent left atrial reentry developing after ablation for atrial fibrillation: ECG characterization and elimination by focal RF ablation.

INTRODUCTION: The complete circuit of reentrant left atrial tachycardias (LATs) occurring after ablation for atrial fibrillation (AF) has not been well described. Identifying discrete isthmuses critical to these LATs may simplify their elimination by catheter ablation. METHODS AND RESULTS: Fifteen patients (all male, 56 +/- 8 years) with 15 reentrant LATs following AF ablation underwent activation and entrainment mapping. Eleven patients (11 LATs) had a single localized site with low amplitude (0.16 +/- 0.05 mV), fractionated long duration (131 +/- 23 msec) electrograms coinciding with an isoelectric interval of 106 +/- 24 msec between flutter waves on all 12 ECG leads. Three-dimensional mapping and entrainment revealed this site to be a narrow markedly slowly conducting isthmus adjacent to ablated left (n = 8) or right (n = 3) pulmonary vein (PV) ostia, and critical to nine small diameter (15 +/- 3 mm) and two large diameter (49 +/- 2 mm) circuits. One radiofrequency (RF) application on this isthmus eliminated LAT in all 11 patients. Four patients (four LATs) with large circuits around the mitral annulus and/or PV ostia lacked isoelectric ECG intervals and slow-conducting isthmuses and required multiple RF applications across anatomically wide, rapidly conducting isthmuses. CONCLUSION: Focally ablatable narrow isthmuses of slow conduction are critical for the majority of reentrant LAT occurring after ablation for AF. The role and presence of these isthmuses can be anticipated by observing significant isoelectric intervals between flutter waves on all 12-surface ECG leads. Their distinctive electrophysiological characteristics allow their identification and elimination by simple RF ablation.

Atrial Fibrillation↗
PubMed2006

Percutaneous ablation of atrial fibrillation: for whom and how?

Recent developments in our understanding of atrial fibrillation (AF) have focused on the key role of pulmonary vein initiators of multiple wavelet reentry in the atria. Percutaneous catheter ablation of atrial fibrillation is commonly performed by electrical disconnection of pulmonary vein myocardium from the left atrium. As a result, pulmonary vein foci can no longer drive the atria into fibrillation. At present, the procedure is offered to patients with paroxysmal atrial fibrillation refractory to multiple antiarrhythmic agents. For patients with persistent atrial fibrillation, supplementary linear lesions in the left atrium may be necessary. Success rates (AF elimination) are 90% without drugs in case of paroxysmal atrial fibrillation and 80% for persistent atrial fibrillation. Complications including pulmonary vein stenosis are uncommon.

Atrial Fibrillation↗
PubMed2005

Acute pyloric spasm and gastric hypomotility: an extracardiac adverse effect of percutaneous radiofrequency ablation for atrial fibrillation.

OBJECTIVES: This study sought to describe a new adverse effect of percutaneous radiofrequency (RF) ablation for atrial fibrillation (AF). BACKGROUND: Extension of the RF lesion beyond atrial myocardium may affect mediastinal structures other than the esophagus. METHODS: Circular mapping-guided isolation of the pulmonary veins was performed in two different electrophysiology laboratories, either individually and supplemented by ostial and posterior left atrial (LA) ablation or two by two with a series of ostial and posterior LA lesions. The RF energy was delivered point by point through a 5-mm open-tip irrigated catheter (40 W maximum) or an 8-mm-tip catheter (45 W maximum). RESULTS: In four (two in each electrophysiology laboratory) of 367 patients undergoing catheter ablation for AF, abdominal pain and distension developed within 48 h after the procedure. Investigation showed acute pyloric spasm and gastric hypomotility, probably the result of LA endocardially delivered RF affecting the periesophageal vagi. Complete spontaneous recovery occurred in two patients, but laparoscopic esophagojejunal anastomosis and endoscopic intra-pyloric Botulinum toxin injection, respectively, were performed to remedy delayed gastric emptying in two patients. CONCLUSIONS: Thermal injury during endocardial LA RF energy delivery may extend into the mediastinum and rarely may involve the periesophageal nerves, resulting in a syndrome of acute delayed gastric emptying. Marked anatomic variability of periesophageal vagi renders it difficult to reliably avoid the area overlying this plexus, therefore, we advocate a reduction in maximum RF power and application duration on all of the posterior LA to try to avoid this complication.

Abdominal Pain↗
PubMed2005

Optimizing sequential biventricular pacing using radionuclide ventriculography.

BACKGROUND: Biventricular pacemakers are usually programmed with the default setting of synchronous biventricular pacing, although the ventricles may be paced sequentially. Whether this parameter is important for optimizing resynchronization therapy is not clear. OBJECTIVES: The purpose of this study was to investigate whether sequential pacing acutely improves left ventricular ejection fraction (LVEF) and dyssynchrony and to assess the feasibility of nuclear ventriculography for device optimization. METHODS: Twenty-seven patients implanted with a biventricular pacemaker or implantable cardioverter-defibrillator for heart failure were studied. LVEF was measured using planar radionuclide ventriculography during simultaneous biventricular pacing and during sequential pacing at four different interventricular intervals ranging from LV-40 (preexciting the left ventricle by 40 ms) to LV+40 (preexciting the right ventricle). Interventricular and intraventricular dyssynchrony were analyzed by phase analysis at each setting. RESULTS: There was great heterogeneity in individual response to VV interval programming. Twenty-four of 27 patients (89%) had significant changes (both favorable and unfavorable) in LVEF at different interventricular delays, with variations of up to 10% in absolute terms. Simultaneous biventricular pacing yielded maximal LVEF in 9 of 27 patients (33%), with a relative increase in LVEF of 18 +/- 14% by optimized sequential pacing in the remaining patients. Interventricular dyssynchrony varied significantly, with least dyssynchrony at the LV-20 setting (P = .024). There were no significant differences in intraventricular dyssynchrony at the different settings. CONCLUSION: Programming VV intervals has considerable impact on LVEF. However, there is a great degree of variation between patients in response to these settings, requiring individual assessment for device optimization.

Aged↗
PubMed2005

Prospective study of axillary vein puncture with or without contrast venography for pacemaker and defibrillator lead implantation.

Axillary vein puncture may be used to implant pacemaker (PM) or cardioverter defibrillator leads, though usually requires venography. We prospectively compared punctures guided by venography versus a new radiological landmark. In 232 patients, the puncture was guided by injecting diluted contrast material via an ipsilateral peripheral vein (group A, n = 142), or without venography using the intersection of the lateral borders of the second and third rib as a radiological landmark, followed by contrast injection in case of failure (group B, n = 90). We implantated 1-3 leads per patient. In group A, implantation was successful in 135 patients (95%) and in group B in 55 patients (61%, P < 0.001 vs group A). Subsequent contrast injection allowed successful implantations in 34 of 35 patients, with an success rate of 97% for the overall study population of 224 patients. Venous access was achieved after a mean of 10.4 +/- 3.2 minutes of skin incision in group A versus 9.4 +/- 3.0 minutes in group B (ns). Pneumothorax occurred in two patients (1% overall). Thus non-contrast guided puncture using a new radiological landmark was successful in a majority of patients. This technique may be useful in absence of ipsilateral peripheral vein access, or presence of contrast allergy.

Aged↗
PubMed2005

Typical atrial flutter ablation and the risk of postablation atrial fibrillation.

Typical atrial flutter is readily abolished by creating a line of block along the isthmus between the tricuspid annulus and the inferior vena cava. However, postablation atrial fibrillation occurs frequently, and its occurrence increases during the follow-up. Preablation atrial fibrillation is the most important risk factor for postablation atrial fibrillation occurrence. Among patients with preablation atrial fibrillation, patients with drug-induced atrial flutter present a lower risk of postablation atrial fibrillation than patients with spontaneous preablation atrial fibrillation. Patients with preablation lone atrial flutter also present a significant risk of atrial fibrillation development as time passes. Hence, they must be advised of the risk of recurrent symptoms and late atrial fibrillation, and closely followed up despite successful transisthmic ablation. Patients with atrial fibrillation after transcatheter isthmus ablation should be offered catheter-based pulmonary vein isolation, particularly if atrial fibrillation occurs despite continuation of antiarrhythmic drug therapy.

Atrial Fibrillation↗
PubMed2004

Linear cryoablation of the left atrium versus pulmonary vein cryoisolation in patients with permanent atrial fibrillation and valvular heart disease: correlation of electroanatomic mapping and long-term clinical results.

BACKGROUND: The aim of this study was to clarify the role of pulmonary vein isolation (PVI) alone versus left atrial linear lesions in the treatment of permanent atrial fibrillation (AF) in patients with left atrial dilatation and valvular disease. The primary end point was to assess the persistence of sinus rhythm (SR) off antiarrhythmic drugs (AADs) at 2-year follow-up and to correlate clinical outcome with surgical results validated with electroanatomic mapping (EAM). METHODS AND RESULTS: A total of 105 patients with permanent AF undergoing valve surgery were assigned to 3 different groups: in groups "U" and "7," left atrial linear cryoablation was performed, whereas in group "PV" patients, anatomic cryoisolation of pulmonary veins only was performed. In groups U and 7, SR was achieved in 57% of patients, whereas it was achieved in 20% of PV patients during 2-year follow-up. In the first 51 patients, the ablation schemes were validated with EAM. The EAM showed that the U lesion was never obtained: in 59% of these patients, a complete 7 lesion was achieved instead; in the 7 group, a complete 7 lesion was present in 65% of patients, whereas a complete PVI was obtained in 71% of patients. Considering patients in whom a complete 7 lesion was demonstrated with the EAM, SR without AADs was achieved in 86% of patients, whereas only 25% of patients with complete PVI were in SR without AADs. CONCLUSIONS: In patients with permanent AF, left atrial dilatation and valvular heart disease linear lesions in the posterior region of the left atrium are more effective than PVI alone. With cryoablation, the surgical intent is fulfilled in only approximately 65% of the cases. Knowing the real anatomic and electrophysiological effects of surgical ablation is necessary to correctly interpret the clinical outcome.

Aged↗
PubMed2004

"Dormant" pulmonary vein conduction revealed by adenosine after ostial radiofrequency catheter ablation.

INTRODUCTION: The endogenous nucleoside adenosine is an important intermediate in cellular metabolism, a regulator of function in many organ systems, and a pharmacologic agent with potent electrophysiologic effects. We studied the effects of adenosine on the activation of the pulmonary veins (PVs) after successful ostial isolation in patients with atrial fibrillation (AF). METHODS AND RESULTS: Twenty-nine patients (21 male; mean age 54 +/- 10 years) with refractory highly symptomatic persistent (n = 9) or paroxysmal (n = 20) AF were included in the study. PV isolation was performed using radiofrequency catheter ablation guided by a multipolar basket catheter (Constellation, Boston Scientific). After successful PV isolation, we studied the effects of intravenous adenosine (12-18 mg) on activation of the upper PVs. A total of 83 PVs were successfully isolated. After adenosine, PV activity was recorded in 10 (34%) of 29 left upper PVs studied and in 3 (13%) of 24 right upper PVs, coupled to atrial activity for 20 +/- 7 seconds (adenosine positive). In 8 (62%) of 13 cases, PV potentials were recorded in the distal electrodes of the basket catheter only. Dissociated PV rhythms (N = 8) present after PV isolation disappeared after adenosine for 18 +/- 7 seconds, even if reconduction was missing. In 14 patients (48%), a second EP study was performed for recurrence of AF. Adenosine-positive PVs had a nonsignificant higher rate of recovery of conduction than adenosine-negative veins (71% vs 35%, P = 0.095). CONCLUSION: Adenosine induces transient conduction in 25% of PVs following successful isolation. Further studies are necessary to determine the physiologic or pathophysiologic role of adenosine-induced reconduction in human hearts or other organ systems.

Adenosine↗
PubMed2004

QRS subtraction and the ECG analysis of atrial ectopics.

The recognition of the ubiquitous role of short coupled ectopics in the initiation of paroxysmal atrial fibrillation has renewed interest in their localization with the ultimate aim of facilitating their neutralization by catheter ablation. The P-waves resulting from such ectopics are partly or completely concealed by the QRST of the preceding beat and therefore their morphology has been underutilized for localization purposes. Subtraction has been the most commonly used technique for QRST suppression and though an averaged template offers a higher signal-to-noise ratio, the immediately preceding QRST provides the best match between template and target and allows simple, nearly real-time, and accurate subtraction without distorting the underlying P-wave. Algorithms derived from clinical tachycardias as well as pacemapping have permitted a rational analysis and accurate prediction (81%) of the correct pulmonary vein of origin. Other nonpulmonary sources may also be similarly localized, particularly with the help of a catalogue of pacemaps from various sites. Incessant arrhythmia and frequent aberrancy limit the effectiveness of QRST suppression by subtraction. Further improvements in the localizing resolution of the P-wave may depend upon knowledge of the relationship between recording electrodes and the underlying atria.

Atrial Fibrillation↗
PubMed2004

Catheter ablation for atrial fibrillation: mechanism-based curative treatment.

The considerable cumulative morbidity and mortality burden resulting from atrial fibrillation has prompted renewed efforts to seek curative and widely applicable therapies. Currently used drugs are not only frequently ineffective at eliminating fibrillation, but may actually be life threatening. Extensive surgery involving both atria has shown that atrial fibrillation can be eliminated in most, if not all, patients, but at a significant cost. The recent discovery of the pivotal role that myocardial extensions into the pulmonary veins play in the initiation, and probably also the maintenance, of atrial fibrillation, has provided a relatively limited target conducive to catheter-based interventions. In experienced hands, paroxysmal atrial fibrillation can be eliminated in more than 85% of patients by a percutaneous intervention lasting less than 3 h with an attendant nonlethal complication risk of 1 to 2%. Thromboembolic complications and pulmonary vein stenosis are the principal complications that may result from this treatment, but their incidence is decreasing. Success rates in patients with persistent or permanent atrial fibrillation are lower, and it is anticipated that increased understanding of the underlying mechanisms will allow doctors to identify those subsets with the greatest potential for benefit from percutaneous catheter-based interventions. Such progress may allow doctors to extend the benefits of eliminating atrial fibrillation to the widest possible range of patients with this recalcitrant disorder.

Atrial Fibrillation↗
PubMed2003

Nonpulmonary vein foci: do they exist?

Though the majority of foci triggering atrial fibrillation (AF) have been mapped to the pulmonary veins (PV), recurrence of paroxysmal AF after isolation of all four pulmonary veins indicates the presence of other foci. In a series of 160 consecutive patients who underwent PV ablation, endocardial mapping of AF and ectopy recurring after PV isolation was performed. Thirty-six patients (24%) had a total of 85 non-PV foci; 39 were mapped to the ostia of ablated PVs, 30 to the posterior left atrium (LA), 5 to other parts of the LA, 5 to the right atrium (RA), 4 to the coronary sinus (CS), and 3 to the superior vena cava (SVC) (including one persistent left SVC). Mapping was confirmed by successful ablation. At least 16 foci could not be localized and after a follow-up of 8 +/- 6 months, 68% of patients were free of AF without any antiarrhythmic treatment. The occurrence of non-PV foci correlated with recurrence of AF, perhaps as a correlate of insufficient ostial ablation. These data reinforce the requirement for more proximal disconnection of the PVs by performing ablation within the LA. In patients with non-PV foci that are difficult to map conventionally, the use of surface ECG data, or multielectrode contact or noncontact mapping arrays, or substrate modifying/excluding ablation may be helpful in ablating these foci and therefore eliminating AF.

Atrial Fibrillation↗