Suppression of Storms of Ventricular Tachycardia by Epicardial Ablation of Isolated Delayed Potential in Noncompaction Cardiomyopathy

A 65‐year‐old recipient of an implantable cardioverter defibrillator suffering from ventricular noncompaction developed storms of ventricular tachycardia (VT). Epicardial voltage mapping revealed the presence of a large low‐voltage area in the left ventricular apical and inferoposterior wall, and isolated delayed potential was recorded over 1.5 cm in the posterior border between low and normal myocardial voltage. Pacemapping at the delayed potential recording site produced two different QRS depending on pacing output strength, and these two QRS morphologies were similar to clinically documented VTs. During one of the VTs, a mid‐diastolic potential was recorded from the site with the delayed potential, and rapid pacing produced concealed entrainment. After epicardial radiofrequency ablation of the isolated delayed potential, VTs were noninducible and the VT storm was suppressed.     

Epicardial Macroreentrant Ventricular Tachycardia Associated with a Left Ventricular Aneurysm

A 62‐year‐old man with severe coronary artery disease and a left ventricular aneurysm underwent catheter ablation of ventricular tachycardia (VT) with right bundle branch block QRS morphology. Endocardial bipolar voltage mapping with standard threshold settings demonstrated no low‐voltage areas within the aneurysm. Catheter ablation of the epicardial surface of the aneurysm eliminated the VT. Endocardial bipolar voltage mapping with any other settings could not predict the site of the epicardial arrhythmogenic substrate whereas endocardial unipolar voltage mapping could. Endocardial unipolar voltage mapping may be helpful for predicting epicardial arrhythmogenic substrates. (PACE 2012; 35:e13–e16)     

Localized reentry. Mechanism of induced sustained ventricular tachycardia in canine model of recent myocardial infarction.

This study was undertaken to investigate the mechanism underlying sustained monomorphic ventricular tachycardia (VT) in late experimental canine myocardial infarction. The hypothesis that sustained and "organized" continuous electrical activity (CEA) displaying a reproducible pattern with recurrent components recorded by bipolar endocardial, intramural, or epicardial electrodes in 10 animals during electrically induced sustained monomorphic VT represented reentrant excitation in an anatomically small area of the ventricle, was evaluated in the light of the following observations: Organized CEA always preceded the first monomorphic ventricular complex (QRS) of VT as well as the discrete local electrograms from closely surrounding sites during the initiation of VT. The site of organized CEA corresponded to the site of origin of sustained VT determined by iso-chronous contour map analysis of activation sequence. Ventricular pacing at rates more rapid than that of VT failed to terminate VT despite ventricular capture unless it transformed CEA into discrete local electrograms. VT could be terminated in three animals, with a single, critically timed premature stimulus delivered at a critically located focus close to the site of CEA, which would result in local capture and interrupted CEA. In six animals, surgical ablation of the site of organized CEA effectively prevented the reinitiation of sustained VT by programmed cardiac stimulation. These data showed that organized CEA and sustained VT were closely associated phenomena and suggested that organized CEA probably represented an important component of the tachycardia circuit.     

Origin of acetyl strophanthidin-induced ventricular arrhythmias.

To examine the origin of digitalis-induced ventricular tachycardia (VT), acetyl strophanthidin (AS) (25 mug/min) was perfused into a limited zone of myocardium in intact anesthetized dogs through a catheter placed fluoroscopically in the left anterior descending artery without ischemia. A second catheter in the great cardiac vein sampled venous effluent from this region. His and left bundle branch depolarizations were recorded and bipolar intramural electrograms from endocardial and epicardial sites within the anterior descending region were obtained. No conduction alterations preceded arrhythmia. Cardiac venous K+ rose from 3.3 +/- to 4.4 +/- 0.2 meq/liter (P less than 0.001), indicating egress from the perfused zone. 10 animals (Group 1) were sacrificed 2 min after onset of VT while 11 (Group 2) continued until fibrillation (4-14 min). All showed normal (endocardial leads to epicardial) transmural depolarization during sinus rhythm, but 10/21 demonstrated reversal, usually late during VT, including 8/11 in Group 2. Epicardial activation preceded fascicular activation and QRS. Recordings from the border and circumflex regions in 10 additional dogs (Group 3) demonstrated activation reversal only in the border zone. Myocardial K+ was reduced (mean 63 +/- 1 mueq/g) and Na+ increased (mean 41 +/- 2 mueq/g) in the perfused zone (nonperfused circumflex area K+ 72 +/- 1, Na+ 33 +/- 1 mueq/g, P less than 0.001 for both); changes were similar in inner and outer ventricular wall. In related experiments, subepicardial injections of AS induced activation reversal within the immediate area, similar to recordings during coronary infusion. Reversed transmural activation with early epicardial depolarization suggest VT arises within myocardium; electrolyte gradients between adjacent regions may be causative.     

Value of Serial Electropharmacological Testing in Managing Patients Resuscitated from Cardiac Arrest

Electrophysiologic studies were performed in 11 patients (9 men, 2 women; mean age: 59.9 yrs) who had survived an episode of cardiac arrest due to ventricular tachycardia (VT) or ventricular fibrillation. The purpose of the studies was to evaluate the usefulness of serial acute drug testing in selecting an effective chronic antiarrhythmic regimen. Ten of the patients were suffering from chronic ischemic heart disease with one or more previous myocardial infarctions while one had no evidence of structural heart disease. A ventricular aneurysm was present in four of them. During control electrophysiologic study, a sustained VT was induced by ventricular stimulation (single and double extrastimuli at various paced ventricular cycle lengths plus bursts of rapid ventricular pacing) in nine of the ten patients (90%) who were studied while not receiving antiarrhythmic drugs; a non-sustained VT was induced in one of them (10%). In three patients (30%) VT could be initiated only by right ventricular stimulation at a side different from the apex (outflow tract). No arrhythmia was observed in the only patient who was studied while taking amiodarone orally (400 mg/day for more than three months). During serial acute drug testing a totally effective drug regimen (successful in preventing the induction of any ventricular arrhythmia) was found in seven of the ten patients (70%) who underwent this procedure and a partially effective drug regimen (a sustained VT was no longer inducible; it was easier to interrupt and it was considerably slower) was found in two patients (20%). None of the nine patients who received chronic antiarrhythmic therapy based on the results of serial acute drug testing died suddenly during a mean follow-up of 14 months (range: 3-28) and only one had a recurrence of cardiac arrest. The latter, however, was taking antiarrhythmic drugs at a dosage less than that proved to be effective during electropharmacological testing. The only patient who refused serial acute drug testing and received an empiric antiarrhythmic therapy died suddenly at the 21st month of follow-up. These results indicate that serial electropharmacological testing is useful in selecting an effective long-term drug regimen in survivors of cardiac arrest.     

Epicardial ablation of ventricular tachycardia associated with isolated ventricular noncompaction

A 52-year-old man presented with sudden onset of palpitations and dizziness. Echocardiogram confirmed the diagnosis of isolated noncompaction of ventricular myocardium with moderated systolic dysfunction, and the electrocardiogram (ECG) revealed ventricular tachycardia (VT), of which the focus seemed to match an area of prominent left ventricular noncompaction on the 12-lead surface ECG. Through the activation mapping from the endo- and epicardium, simultaneously, a discrete potential preceding the QRS during VT was observed at the anterolateral epicardial wall. He subsequently underwent radiofrequency ablation, and VT was successfully eliminated.     

Arrhythmogenic right ventricular cardiomyopathy characterized by recurrent syncope during exercise: A case report

BACKGROUNDArrhythmogenic right ventricular (RV) cardiomyopathy is a rare and currently underrecognized cardiomyopathy characterized by the replacement of RV myocardium by fibrofatty tissue. It may be asymptomatic or symptomatic (palpitations or syncope) and may induce sudden cardiac death, especially during exercise. To prevent adverse events such as sudden cardiac death and heart failure, early diagnosis and treatment of arrhythmogenic RV cardiomyopathy (ARVC) are crucial. We report a patient with ARVC characterized by recurrent syncope during exercise who was successfully treated with combined endocardial and epicardial catheter ablation.CASE SUMMARYA 43-year-old man was referred for an episode of syncope during exercise. Previously, the patient experienced two episodes of syncope without a firm etiological diagnosis. An electrocardiogram obtained at admission indicated ventricular tachycardia originating from the inferior wall of the right ventricle. The ventricular tachycardia was terminated with intravenous propafenone. A repeat electrocardiogram showed a regular sinus rhythm with negative T waves and a delayed S-wave upstroke from leads V1 to V4. Cardiac magnetic resonance imaging showed RV free wall thinning, regional RV akinesia, RV dilatation and fibrofatty infiltration (RV ejection fraction of 38%). An electrophysiological study showed multiple inducible ventricular tachycardia as of a focal mechanism from the right ventricle. Endocardial and epicardial voltage mapping demonstrated scar tissue in the anterior wall, free wall and posterior wall of the right ventricle. Late potentials were also recorded. The patient was diagnosed with ARVC and treated with combined endocardial and epicardial catheter ablation with a very satisfactory follow-up result.CONCLUSIONClinicians should be aware of ARVC, and further workup, including imaging with multiple modalities, should be pursued. The combination of epicardial and endocardial catheter ablation can lead to a good outcome.     

Long-Term Outcome Following Programmed Electrical Stimulation in Patients with High-Grade Ventricular Ectopy

To determine if programmed electrical stimulation (PES) could be utilized to identify patients with high-grade ventricular ectopy at low- or high-risk for sudden cardiac death, we performed PES in 40 patients with high-grade ventricular ectopy refractory to conventional antiarrhythmic agents. Twenty-one patients had a previous myocardial infarction, five had cardiomyopathy, six had hypertension, three had valvular heart disease and five had no known structural heart disease. The mean age was 50 years (range, 18 to 76). During programmed ventricular stimulation, eight patients had inducible sustained (more than 30 seconds) monomorphic ventricular tachycardia (Group I) but in 32 patients sustained ventricular tachycardia was not inducible (Group II). None of the five patients without structural heart disease were inducible while seven out of 21 (33%) patients with previous myocardial infarction had inducible ventricular tachycardia (VT). Antiarrhythmic therapy was instituted in patients with inducible VT; patients without inducible VT did not receive antiarrhythmic agents. In Group I, seven of the eight patients are alive (mean follow-up, 16 months) and in Group II, 28 of the 32 patients are alive (mean follow-up, 17 months). None of the five deaths were sudden. We conclude that in the absence of antiarrhythmic therapy, the incidence of sudden cardiac death is very low in patients with high-grade ventricular ectopy who do not have inducible monomorphic ventricular tachycardia during programmed ventricular stimulation.     

Successful epicardial ablation of idiopathic mitral annular ventricular tachycardia from the great cardiac vein

This case report describes idiopathic ventricular tachycardia (VT) originating from the anterolateral site of mitral annulus. Radiofrequency (RF) energy application at an endocardial site of mitral annulus could not eliminate the tachycardia. The earliest epicardial activation preceding the onset of the QRS complex by 34 ms was found at the great anterior cardiac vein just opposite to the endocardial ablation catheter, pace mapping provided an identical (12/12) match with the VT morphology at the site, and RF ablation effectively eliminated the VT from the great cardiac vein within the coronary venous system.     

Demonstration of Purkinje Potential During Idiopathic Left Ventricular Tachycardia: A Marker for Ablation Site by Transient Entrainment

A Marker for Ablation Site by Transient Entrainment. During VT of QRS morphology with right bundle branch block and left axis deviation in a patient without obvious structural heart disease, entrainment by pacing from the right ventricular outflow tract and high right atrium was demonstrated. During entrainment of VT, a Purkinje potential preceding the QRS and recorded at the left ventricular midseptum was activated by orthodromic impulses in the reentry circuit. The interval between the Purkinje potential and the earliest left ventricular activation was decrementally prolonged with shortening of pacing cycle length. Radiofrequency energy was applied to this site, resulting in successful elimination of VT. Therefore, the Purkinje potential represented activation by an orthodromic wavefront in the reentry circuit, while the orthodromically distal site to this potential showed an area of slow conduction with decremental property.     

Catheter ablation for an incessant form of antiarrhythmic drug-resistant ventricular fibrillation after acute coronary syndrome

A 77-year-old man was admitted with an acute coronary syndrome (ACS), severe heart failure (HF), and repeated ventricular fibrillation (VF) episodes. A single premature ventricular complex (PVC) induced ventricular tachycardia (VT), which degenerated to VF reproducibly. This PVC was eliminated by catheter ablation at the left ventricular posteroseptal region where double Purkinje potentials preceding the ventricular wave had been recorded. The electrical storm disappeared, and programmable stimulation failed to induce any tachyarrhythmias after the ablation. A Purkinje fiber network-related PVC served as a trigger and as a substrate for VT and VF in a case of ACS with HF.     

Reentrant Ventricular Outflow Tract Tachycardia Arising from Focal Scar Detected by Delayed Enhancement Magnetic Resonance Imaging

A 58‐year‐old man was referred to our emergency room with hemodynamically unstable sustained ventricular tachycardia (VT). The morphology of the VT exhibited a left bundle branch block and inferior axis deviation. He had no past history of cardiovascular disease. Echocardiography, cardiac catheterization, cardiac biopsy, gallium scintigram, myocardial scintigram, T1,T2‐weighted magnetic resonance imaging (MRI), and gadolinium‐enhanced cine MRI did not detect any structural heart disease or abnormal cardiac function. However, delayed‐enhancement MRI (DE‐MRI) detected a focal intramural scar within the septal ventricular outflow tract. An electrophysiological study revealed a sustained VT with several morphologies and the entrainment phenomenon. Radiofrequency catheter ablation to the site corresponding to the focal scar detected by DE‐MRI successfully eliminated the VT. (PACE 2012;35:e349–e352)     

In vivo assessment of myocardial stiffness with acoustic radiation force impulse imaging

Acoustic radiation force impulse (ARFI) imaging has been demonstrated to be capable of visualizing variations in local stiffness within soft tissue. Recent advances in ARFI beam sequencing and parallel imaging have shortened acquisition times and lessened transducer heating to a point where ARFI acquisitions can be executed at high frame rates on commercially available diagnostic scanners. In vivo ARFI images were acquired with a linear array placed on an exposed canine heart. The electrocardiogram (ECG) was also recorded. When coregistered with the ECG, ARFI displacement images of the heart reflect the expected myocardial stiffness changes during the cardiac cycle. A radio-frequency ablation was performed on the epicardial surface of the left ventricular free wall, creating a small lesion that did not vary in stiffness during a heartbeat, though continued to move with the rest of the heart. ARFI images showed a hemispherical, stiffer region at the ablation site whose displacement magnitude and temporal variation through the cardiac cycle were less than the surrounding untreated myocardium. Sequences with radiation force pulse amplitudes set to zero were acquired to measure potential cardiac motion artifacts within the ARFI images. The results show promise for real-time cardiac ARFI imaging.     

Origin of electrical activation within the right atrial and left ventricular walls: differentiation by electrogram characteristics using the noncontact mapping system

Clinical data using the noncontact mapping system (Ensite 3000) suggest that characteristics of the reconstructed unipolar electrograms may predict the origin of electrical activation within the atrial and ventricular walls (endocardial vs myocardial vs epicardial origin). Experimental data are lacking. In ten open-chest pigs (mean body weight 62 kg) cardiac pacing was performed at a cycle length of 600 ms with a pulse width of 2 ms and twice diastolic threshold from the endo-, the myo-, and the epicardium, respectively. Pacing was undertaken at three right atrial and three left ventricular sites, and cardiac activation was recorded with the Ensite system. Reconstructed unipolar electrograms at the location of earliest endocardial activation assessed by color coded isopotential maps were analyzed systematically for differences in morphology. The positive predictive value of atrial electrograms exhibiting an initial R wave during pacing for a subendocardial origin (i.e., myocardial or epicardial) was 0.96. The negative predictive value was 0.48. Electrograms generated during myocardial pacing exhibited increased maximal negative voltage and maximal dV/dt (-3 +/- 1.8 mV, -798 +/- 860 mV/ms, respectively) than the electrograms obtained during endocardial (-2 +/- 1 mV, -377 +/- 251 mV/ms, respectively) and epicardial pacing (-2.1 +/- 0.7 mV, -440 +/- 401 mV/ms, respectively, P<0.01 for both parameters). During pacing at the left ventricular wall, occurrence of an initial R wave did not differ significantly between electrograms reconstructed during endocardial and subendocardial pacing. All other characteristics of the unipolar ventricular electrograms analyzed, except latency, did not differ significantly when compared to stimulation depth. Morphological characteristics of unipolar electrograms generated by the noncontact mapping system during pacing of the atrium allowed for discrimination of an endocardial versus a subendocardial origin of activation. At the ventricular level, characteristics of unipolar electrograms did not predict the origin of cardiac activation in this experimental setting.     

Stereotactic body radiation therapy for refractory ventricular tachycardia secondary to cardiac lipoma: A case report

We present the case of a 29‐year‐old man who developed ventricular tachycardia (VT) secondary to a cardiac lipoma located adjacent to the interventricular groove, which could not be fully resected. Antiarrhythmic drugs and endocardial and epicardial ablation failed to prevent VT recurrence. Finally, noninvasive stereotactic body radiation therapy (SBRT) targeting the lipoma was performed, with a total dose of 24 Gy delivered in three fractions. The number of VT episodes was reduced from 189/24 h before SBRT to 0 after the procedure. At 4‐month follow‐up, there were no signs of therapy‐related complications. Our experience suggests that SBRT could emerge as a viable treatment option for patients with cardiac tumors who develop refractory ventricular arrhythmias.     

Electrode Polarity Does Not Alter the Initial Ventricular Activation Sequence During Pacing with Extracardiac Electrodes

Ventricular epicardial mapping was performed in six closed-chest anesthetized dogs to investigate the cardiac electrical response to external pacing. A right thoracotomy was performed, complete A V block was produced by formaldehyde injected into the AV node and a sock electrode array, comprised of 127 unipolar electrodes, was placed over the ventricles. Isopotential and isochronal epicardial maps were generated by computer from the unipolar electrograms. Unipolar stimulation pulses were applied between pairs of different types of cutaneous (metal, carbon) and esophageal (metal) electrodes, and recordings were performed at maximum lung inflation. Isopotential maps recorded during the stimulation artifacts showed that the epicardial electrical field was little affected by the type of electrode but depended mostly on electrode position. A reproducible and relatively uniform apex-to-base potential gradient was regularly produced with anteroposterior and anteroesophageal electrode configurations. This uniform potential gradient induced ventricular activation sequences that showed interindividual differences. Thus, for each dog, the areas of initial activation observed on the isochronal maps during pacing tended to remain the same (i.e., apical, lateral, and anterior) despite changes in the stimulation protocol. Inverting the polarity of the electrodes did not appreciably change the site of origin of activation (81 % remained the same) and activation never originated from the area showing the most negative potential during the stimulation artifact. In conclusion, since electrode polarity does not seem to alter the ventricular activation sequence during cardiac pacing with extracardiac electrodes, the standard nomenclature for cutaneous patches, which defines the negative electrode as the "active" electrode, may have to be revised.     

Electrophysiological Evaluation of Sustained Ventricular Tachyarrhythmias in Idiopathic Dilated Cardiomyopathy

Sustained ventricular tachyarrhythmias and sudden death are particularly prevalent in patients with idiopathic dilated cardiomyopathy (IDC). In contrast to patients with ischemic heart disease, the value of electrophysiological stimulation (EPS) in patients with IDC has not yet been established. To clarify the role of EPS in these patients, we studied 19 patients (58 +/- 11 years) with IDC who had symptomatic ventricular tachycardia (VT) or ventricular fibrillation (VF). The mean left ventricular ejection fraction was 26 +/- 9%. Ten patients had survived out-of-hospital cardiac arrest, eight had documented sustained monomorphic VT and one patient had non-sustained VT associated with syncope. Thirteen of the 19 patients (68%) had their clinical ventricular tachyarrhythmias induced at EPS (12 VT, 1 VF). In nine of 13 patients (69%), the arrhythmias were subsequently suppressed during serial electrophysiological drug testing. During 17 +/- 11 months of follow-up, 10/19 (53%) patients experienced recurrence of their arrhythmias and nine out of 19 (47%) patients died; six died suddenly and three secondary to heart failure. There was no difference in arrhythmia recurrence between patients with and without inducible ventricular tachyarrhythmias at initial study. Furthermore, suppression of arrhythmia during serial testing did not predict outcome; recurrences were observed in five out of nine patients whose arrhythmias were suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Catheter Ablation of Electrical Storm Due to Monomorphic Ventricular Tachycardia in Patients with Nonischemic Cardiomyopathy: Acute Results and Its Effect on Long‐Term Survival

Background: Electrical storm due to recurrent ventricular tachycardia (VT) in patients with implantable cardioverter defibrillator (ICD) can adversely affect their long‐term survival. This study evaluates the efficiency of the radiofrequency catheter ablation of electrical storm due to monomorphic VT in patients with idiopathic dilated cardiomyopathy (DCM) and assesses its long‐term effects on survival. Methods and Results: Between April 2004 and October 2008, 13 consecutive patients (nine men, mean age 56.8 ± 17.8 years) with DCM and electrical storm due to monomorphic VT who had ICD underwent 17 catheter ablation procedures, including four epicardial, at our center. Acute complete success was defined as the lack of inducibility of any VT at the end of procedure during programmed right ventricular stimulation and was achieved in eight patients (61.5%). During a median follow‐up of 23 months (range 3–63 months) nine patients (69%) were alive and eight patients (61.5%) were free from VT recurrence. Among those with acute complete (n = 8) and partial (n = 5) success, seven patients (87.5%) and one patient (20%) were free from any VT recurrence and ICD therapy, respectively (P = 0.025). Among those with acute complete and partial success, seven patients (87.5%) and two patients (40%) were alive, respectively (Mantel‐Cox test P = 0.082). Among those who had an initially failed endocardial ablation (n = 8), four underwent further epicardial ablation that was completely successful in three patients (75%). Conclusion: Catheter ablation in patients with DCM and electrical storm due to monomorphic VT who had an ICD prevents further VT recurrence in 61.5% of the patients. Complete successful catheter ablation may play a protective role and was associated with reduced mortality during the follow‐up period. More aggressive ablation strategies in patients with initially failed endocardial ablation might improve the long‐term survival of these patients; however, further studies are needed to clarify this issue. (PACE 2010; 33:1504–1509)     

Sinus Rhythm Mapping in a Canine Model of Ventricular Tachycardia

The relationship between electrograms recorded during sinus rhythm and the activation sequence during ventricular tachycardia induced by programmed stimulation was investigated in a canine model of myocardial infarction. Thirteen dogs were studied 3 days (n = 10) or 14 days (n = 3) after coronary occlusion. Sixty-three unipolar electrograms were simultaneously recorded with a sock electrode array connected to a digital recording system, and analyzed by computer. Bipolar electrograms were recorded sequentially from the same sites with an analog recorder. Categories of unipolar electrograms were defined with reference to the QRS complex during sinus rhythm as follows: Class A included electrograms with an intrinsic deflection inscribed within the QRS complex, class B included those which did not exhibit any intrinsic rs deflection, and class C included those with an intrinsic deflection inscribed later than QRS. The epicardial distribution of each class of electrograms was significantly different between the preparations with, and those without inducible tachycardia (72% versus 63% of electrograms being in class A, 20% versus 35% in class B, and 8% versus 2% in class C; p less than 0.005). When tachycardia was inducible, class C epicardial electrograms were located in an area extending across the region of infarction, which corresponded to the common reentrant pathway of figure-of-eight patterns mapped during tachycardia. When ventricular tachycardia was not inducible, class B electrograms were recorded all over this region. The morphology of bipolar electrograms had no predictive value in identifying the common reentrant pathway. These results support the view that the inducibility of reentrant tachycardia is dependent upon critically located delayed activity detected during sinus rhythm by unipolar recordings.     

Perioperative biventricular pacing leads to improvement of hemodynamics in patients with reduced left-ventricular function--interim results

BACKGROUND: Cardiac resynchronization therapy (CRT) has been introduced as a new therapeutic modality in patients with chronic heart failure. However, most studies have investigated the hemodynamic effects in congestive, but not postoperative heart failure. OBJECTIVE: The following study investigates hemodynamic effects of perioperative temporary biventricular pacing in patients undergoing open heart surgery.In 54 patients one left and one right ventricular epicardial wire was placed during open heart operations. Hemodynamic parameters were measured immediately after the operation and 6 as well as 24 hours postoperatively. Transesophageal echocardiography was performed 1 hour postoperatively. RESULTS: Of the 54 patients (59.2%), 32 responded to biventricular pacing with an increase in cardiac output; in these patients synchronized ventricular contraction could be verified echocardiographically. This hemodynamic benefit persisted 6 hours and 24 hours postoperatively. The remaining 22 patients did not show any hemodynamic improvement from biventricular stimulation. CONCLUSION: Biventricular pacing leads to significant rise in cardiac output in approximately 59% of patients with severely reduced left ventricular function and widened QRS complexes. Further studies are necessary to define clearly the clinical characteristics of patients who show remodeling by CRT.